8 From Ehrenfest to Schro¨ dinger

Our next five remarkable physicists were born in the eight years from 1880 to 1887.

Two came from Austria and one from each of Denmark, England and Germany.

Paul Ehrenfest (1880–1933)

In Austria-Hungary the laws controlling and restricting Jewish life had been

greatly relaxed by the eighteen-seventies, after which Jews began first to

enter and then to dominate Viennese intellectual and cultural life. Their

position in commerce and finance also grew to one of great strength. Unfortunately

anti-Semitism grew stronger at the same time and boys who were

visibly Jewish suffered from it constantly. In Austria, as in Germany, the

universities were citadels of anti-Semitism and it was difficult for even the

most distinguished Jewish scholars to obtain professorships.

The physicist Paul Ehrenfest was born in Vienna on January 18, 1880.

His parents had moved to the imperial capital about twenty years earlier

from Loschwitz, a small Jewish village in Moravia. His father Sigmund

worked in a textile mill until he married Johanna Jellinek, the daughter of

a merchant in the same village, and set up a grocery business. The business

thrived and, by the time their son Paul had been born, the family was reasonably

well off. They had four older sons, Arthur (1862), Emil (1865), Hugo

(1870) and Otto (1872); a daughter was lost at birth. As the youngest by eight

years, born when his father was forty-two and his mother thirty-eight, Paul

was the baby of the family, very much his father’s favourite. When he was

ten years old his mother died of breast cancer; her place in his upbringing was

taken by his widowed maternal grandmother. Paul’s older brothers played a

major role in his early life. Arthur was completing his studies at the Technische

Hochschule, Emil was his father’s right-hand man in the business,

while Hugo and Otto were going through secondary school. In due course

Paul too passed through the school system, entering the akademisches

Gymnasium in 1890 but transferring in 1897 to the Kaiser Franz Josef Gymnasium

to join his friend Gustav Herglotz for the last two years of school.

In October 1899 Paul Ehrenfest enrolled at the Technische

Hochschule, listing chemistry as his major field, but also taking courses in

260 From Ehrenfest to Schr ¨ odinger

a wide range of other scientific subjects, including mathematics. Herglotz,

already recognized as a promising mathematician, was at the University of

Vienna. However, they were able to maintain their friendship and to become

acquainted with other young mathematicians, particularly Hans Hahn and

Heinrich Tietze. The four of them often took walks together in the hills of

the Wienerwald. University students in the German-speaking world, as we

know, were not obliged to limit themselves to a single institution, but could

attend the lectures of particular professors wherever they might be found.

Thus Hahn studied at Strasbourg, Munich and G¨ ottingen, while Herglotz

went off to Munich to study astronomy, and Tietze joined him there after

military service.

By that time Ehrenfest was certain that he wanted to be a theoretical

physicist, due to the influence of Boltzmann, whose course on the mechanical

theory of heat he had been taking. It was Boltzmann who initiated

Ehrenfest into both the substance and the spirit of theoretical physics, as he

did for so many others, and the Boltzmann influence was to shape Ehrenfest’s

own teaching and research in the years to come. After Boltzmann left Vienna

for Leipzig in 1900, Ehrenfest stayed on for another year before migrating to

Paul Ehrenfest (1880–1933) 261

Go¨ ttingen, where he found a much richer scientific life than he had known

in Vienna. He signed up for no fewer than fifteen courses in the first year,

gradually reducing the load as the year went on. While most of these were

on physics, it was the mathematical lectures which he found most exciting,

particularly Hilbert on potential theory and Klein on mechanics.

Among the physics students in Go¨ ttingen was a young Russian

woman, Tatyana Alexeyevna Afanassjewa, who was accompanied by her

aunt Sonya. Her father, the chief engineer of the Imperial Russian Railways,

had died when she was still a child, and she went to live with a childless

uncle, who was a professor at the Technische Hochschule in St Petersburg.

During the period leading up to the First World War, St Petersburg offered

special university-level institutions for women, which to some extent shadowed

the imperial university (then still reserved for men). Tatyana attended

first the women’s paedagogical school and then the institution which offered

women courses in arts, sciences and law. She shone in mathematics and

had gone on to study physics at the Georgia Augusta, where she met Paul

Ehrenfest. Before long the two young physicists had decided on marriage.

She was just a few years older than he was and imposed various conditions:

among them that he must read the novels of Tolstoy as soon as possible

and was never to smoke tobacco. There was also the problem that Paul

was Jewish and Tatyana was Russian Orthodox. The laws of the Austro-

Hungarian empire did not permit the marriage of a Jew to a Christian. Such

a marriage could take place only if the couple officially declared themselves

‘unchurched’, and foreswore all religious affiliations.

First, however, Ehrenfest needed to complete his Ph.D. thesis. He

decided to study under Lorentz in Leiden, while working his way through

the novels of Tolstoy. After a quick trip back to Vienna to see Boltzmann,

who had now returned from Leipzig, Ehrenfest spent some time with his

fiance´e in Go¨ ttingen. He then fitted in an Italian tour, spent a year working

on his thesis in Vienna, completed it in Dubrovnik and had it accepted in

June 1904. That summer, with his doctorate in hand, Ehrenfest was ready

to marry and Tatyana, who had remained in Go¨ ttingen until then, joined

him in Vienna. They proceeded to comply with the formalities of renouncing

their respective religions and were married in December that year. He

promised her that before long they would move to Russia and settle there.

Fortunately both Paul and Tatyana had inherited small incomes,

which made it possible for them to maintain a modest life-style and continue

with scientific work. To start with they stayed on in Vienna, where

their life was centred around the university. Although Paul held no position

262 From Ehrenfest to Schr ¨ odinger

there, he continued to participate actively in the Boltzmann seminar with

Lise Meitner and others, and continued to devour books at a huge rate.

Tatyana went through a serious illness early that summer – mumps, with

high fever and delirium. In 1905 their first child was born, a daughter named

after her mother. The following spring they left Vienna, never to live there

again. After a summer in Switzerland they returned to Go¨ ttingen, where

Paul was invited by Klein to talk at his seminar about some joint work on

statistical thermodynamics that he and Tatyana had just completed.

One of the consequences of her renunciation was that it would be

difficult for Tatyana to return to her homeland, since Czarist Russia was

reluctant to allow entry to non-believers, but fortunately she was able to

persuade the Russian consul in Vienna to grant the necessary visas. In the

autumn of 1907 they moved to St Petersburg, where Pavel Sigismondovich

Ehrenfest, as he was known there, was given a warm welcome. During

the five years they lived in Russia the Ehrenfests spent their summers at

Kanuka, a tiny Estonian village on the Gulf of Finland some 90 or 100 miles

west of St Petersburg. Boltzmann had been writing a review article on

statistical mechanics for the Encyclopaedia of the Mathematical Sciences

which Klein was organizing, but after Boltzmann’s suicide Klein turned to

Ehrenfest to replace him. In addition to this, Ehrenfest wasted a lot of time

trying to qualify for the Magister, the essential prerequisite for a faculty

position in Russia; his research doctorate was irrelevant. Paul could speak

Russian tolerably well and gave some exemplary lectures on the differential

equations of mathematical physics at the Polytechnic Institute.

Tatyana published her first paper in theoretical physics in 1905 and

went on publishing during these Russian years. In 1910 she gave birth to a

second child, another daughter, named Anna. The Ehrenfests began to feel

short of money and so Paul tried again to get his foot on the bottom rung of

the academic ladder by becoming a Privatdozent, first at Leipzig and then at

Munich, but without success. Early in 1912 he set out to visit other people

who might be able to help, including Planck in Berlin, Herglotz in Leipzig

and Sommerfeld in Munich, but in vain. He returned to Vienna to consult

his brothers Arthur, Emil and Otto; the fourth brother Hugo had emigrated

to America, and Paul considered following his example. He went to Brno

to see his old friend Tietze and to Prague to stay with the Einsteins. Long

afterwards Einstein recalled that ‘within a few hours we were true friends –

as though our dreams and aspirations were meant for each other’. They

played the Brahms sonatas for violin and piano. He also was a success with

their little son, the seven-year-old Hans Albert.

Paul Ehrenfest (1880–1933) 263

Einstein was a full professor at Prague but had already decided to move

back to Zu¨ rich, where he was going to be professor at his alma mater, the

ETH; who could be a better successor in Prague than Ehrenfest? However,

Prague, being in the Austro-Hungarian empire, required a formal religious

affiliation. Although Einstein assured him that this was just a formality,

which no-one took seriously, Ehrenfest’s conscience would not allow him

to conceal the renunciation he had made in order to marry Tatyana. When

he saw Ehrenfest off at the railway station, Einstein said that he would try to

find an opening for him in Zu¨ rich. Meanwhile every effort was being made

to persuade Ehrenfest to overcome his scruples and accept the position in

Prague.

At this point Ehrenfest received a letter from Lorentz, whom he had

not seen for nine years, congratulating him on his Encyclopaedia article:

‘highly interesting’, ‘beautiful and profound’. Lorentz went on to say that

he had decided to give up his position at the University of Leiden, after

thirty years, and retire to nearby Haarlem. He had been hoping to persuade

Einstein to succeed him, but Einstein was already committed to the Zu¨ rich

post. Lorentz then made enquiries about the suitability of Ehrenfest for

Leiden. Sommerfeld wrote that ‘he lectures like a master. I have hardly ever

heard a man speak with such fascination and brilliance. Significant phrases,

witty points and dialectic are all at his disposal in an extraordinary manner.

His way of handling the blackboard is characteristic. The whole disposition

of his lecture is noted down on the board for the audience in the most

transparent possible way. He knows how to make the most difficult things

concrete and intuitively clear. Mathematical arguments are translated by

him into easily comprehensible pictures.’ Lorentz wanted to know whether

Ehrenfest would be interested in coming to Leiden.

Meanwhile the Ehrenfests had set off on a cruise down the river Volga;

they were away two weeks and on their return found a letter from Sommerfeld

offering Ehrenfest the position of Privatdozent in Munich, followed by

the one from Lorentz. Deeply moved, both by the nature of Lorentz’ enquiry

and by the delicate way in which it was put, he wrote a long and intimate

letter in reply, saying that only a chair in Switzerland would appeal to him

more. Because the appointment had to be made by the government, there

was some delay; then near the end of September it was confirmed, and the

Ehrenfests could prepare to move to Leiden and settle down. They arrived

with two daughters; a third child was born, in May 1915, a boy named Paul

after his father, and then in August 1918 another, Vassily, who was afflicted

with Down’s syndrome.

264 From Ehrenfest to Schr ¨ odinger

When they arrived in October 1912 they had been given a warmreception

and Lorentz could not have been more helpful. Once the formalities

were over, one of the first things Ehrenfest did was to attend a special meeting

of the Berlin Academy held in Go¨ ttingen, where he had the opportunity

to see both the older generation of German physicists and some of the new

people, such as Courant and Weyl, also the exotic Lindemann. Meanwhile

Tatyana was planning their new house, on an open plan quite different from

the traditional design. When it was built it proved to be more costly to maintain

than they could afford. The hospitable Ehrenfests liked to entertain

rather informally; they were vegetarians, offered no alcoholic drinks and

did not permit smoking.

Just before Einstein moved to Berlin he spent a week in Leiden,

lecturing on his latest ideas and going to see his old friend and mentor

Lorentz. During the FirstWorldWar, in which the Netherlands was neutral,

Ehrenfest kept trying to persuade Einstein to visit Leiden again. Eventually

the bureaucratic difficulties were overcome and Ehrenfest was able to bring

Einstein and Lorentz together once more:

in his usual way, Lorentz first saw to it at dinner that Einstein felt

himself enveloped in a warm and cheerful atmosphere of human

sympathy. Later, without any hurry, we went up to Lorentz’ cozy and

simple study. The best easy chair was carefully placed in position next

to the large work-table for the esteemed guest. Calmly, and to forestall

any impatience, a cigar was provided for the guest, and only then did

Lorentz quietly begin to formulate a finely honed question concerning

Einstein’s theory of the bending of light in a gravitation field. Einstein

listened to the exposition, sitting comfortably in the easy chair and

smoking, nodding happily, taking pleasure in the masterly way

Lorentz had rediscovered, by studying his works, all the enormous

difficulties that Einstein had needed to overcome before he could lead

his readers to his destination, as in his papers, by a more direct and less

troublesome route. But as Lorentz went on and on, Einstein began to

puff less frequently on his cigar. He sat up straighter and more intently

in his armchair. When Lorentz had finished, Einstein sat bent over the

slip of paper on which Lorentz had written mathematical formulae to

accompany his words as he spoke. The cigar was out, and Einstein

pensively twisted his finger in a lock of hair over his right ear. Lorentz,

however, sat smiling at an Einstein completely lost in meditation,

exactly the way a father looks at a particularly loved son – full of

Paul Ehrenfest (1880–1933) 265

confidence that the youngster will crack the nut he has given him, but

eager to see how. It took quite a while, but suddenly Einstein’s head

shot up joyfully; he had it. Still a bit of give and take, interrupting one

another, a partial disagreement, very quick clarification and a

complete mutual understanding, and both men with beaming eyes

skimming over the shining riches of the new theory.

Even more than usual this particular meeting with Einstein left

Ehrenfest inspired and invigorated. They always played violin and piano

sonatas when they met. Ehrenfest’s favourite composer had been Beethoven.

He also played and enjoyed music from Haydn to Brahms, but he had never

particularly liked the music of Bach. Einstein opened the world of Bach’s

music to his friend in Leiden, and Ehrenfest was completely captivated.

Once the war was over, Ehrenfest made a determined effort to persuade

Einstein to move to Leiden from Berlin. Einstein said no to this, but agreed

to a regular visiting professorship, which brought him to Leiden for three or

four weeks annually from 1920 onwards. Already the anti-Einstein faction

was gathering strength in Berlin; the visits he made to Leiden came as a

welcome relief from their attacks.

However, all was not well with Ehrenfest. He was partially estranged

from Tatyana, who had gone back to St Petersburg. He took very personally

the growing threat posed to his fellow scientists by the rise of the Nazi party

in Germany. At the same time he seems to have felt overwhelmed and inadequate

to deal with the continuing change taking place in physics during

the early 1930s. Much as his students loved him, he lost his self-confidence

more and more. Niels Bohr wrote that ‘he is a very clear-sighted man, fertile

in ideas, but his temperament is so troubled I have never encountered anything

like it’. Increasingly prone to depression and bizarre behaviour, the end

came in Amsterdam on September 25, 1933, when he committed suicide at

the age of fifty-three, after shooting and blinding the mentally handicapped

Vassily, then aged fourteen.

Afterwards Einstein wrote of Ehrenfest that ‘he was not only the best

teacher in our profession I have ever known; he was also passionately preoccupied

with the development and destiny of men, especially his students.

Unfortunately the accolades of his students and colleagues were not enough

to overcome his deep-rooted sense of inferiority and insecurity’. Tatyana,

‘whom he loved’, said Einstein, ‘with a passion the likes of which I have not

often witnessed in my life’, was in St Petersburg when the tragic events took

place. She returned to Leiden and spent the rest of her life there. Although

266 From Ehrenfest to Schr ¨ odinger

she never completed a doctorate or held a regular university teaching post,

her writings substantially enriched physics in the Netherlands. She wrote

two major monographs in the 1950s, enlarging her readership by publishing

in English as well as Dutch. Her last work, published in 1960 when she was

eighty-four, was a treatise on the teaching of mathematics. The surviving

son Paul was killed in an avalanche while skiing in the French alps in 1939;

Tatyana lived until 1964.

Max Born (1882–1970)

In these pages, we follow the fortunes of several of the physicists who had

to leave Germany after the Nazis came to power.We have already seen how

Lise Meitner went to Sweden and Albert Einstein to the USA. Later we will

describe how Erwin Schro¨ dinger settled in Ireland. Of course there were

many others. No two cases were exactly alike, but since Max Born was

one of the founders of quantum mechanics and he wrote an informative

autobiography, I have chosen him as the subject of the next profile.

The son Max of Gustav and Margarethe Born was born on December

11, 1882, in Breslau, the chief city of what was then the Prussian province

of Silesia. Gustav Born was a well-known embryologist who occupied a

chair at the University of Breslau, and whose contributions to embryology

Max Born (1882–1970) 267

anticipated some modern developments in our knowledge of sex hormones.

His wife Margarethe (n ´ee Kauffmann) came from a wealthy Silesian family

in the textile business; she died from gallstones when Max was only four

years old. It was probably from her that her son inherited his life-long love

of music; one of his most treasured possessions was an album that had

belonged to his mother, containing autographs of Johannes Brahms, Clara

Schumann, Xaver Scharwenka, Pablo Sarasate and many other celebrated

musicians. For the four years after the loss of their mother, Max and his

younger sister K¨athe were placed under the care of governesses. In 1890 their

father married again, and, although his second wife Bertha (n´ee Lipstein)

proved an admirable stepmother, she never quite replaced Margarethe in

the affections of her two stepchildren.

The family home, with its atmosphere of scientific and general culture,

provided a stimulating environment during Max’s formative years.

His father’s circle of friends at this time included Paul Ehrlich, the pioneer

of chemotherapy, and the bacteriologist Albert Neisser. The young

Born’s schooling at Ko¨ nigWilhelms Gymnasium in Breslau was of the usual

humanistic type, with Latin, Greek and German as the principal objects

of study, together with some mathematics, physics, history and modern

languages. Although Born does not appear to have been a particularly outstanding

scholar, the enthusiasm of his mathematics teacher, the geometer

Heinrich Maschke, who also taught a little physics, communicated itself

to him. At this time Marconi’s experiments on wireless telegraphy were

becoming known, and Maschke repeated them with some of his pupils. He

succeeded in transmitting a signal to an adjoining room. Born used to recall

his feeling of chagrin when his headmaster, summoned from his humane

studies to behold the latest miracle of technology, was not in the least

impressed.

Shortly before Born graduated from the gymnasium in 1901, his father

died. Following paternal advice not to specialize too early at the university

but to sample lectures on a variety of subjects before coming to any decision

on his future career, Born started by attending courses on chemistry, zoology,

philosophy, logic, mathematics and astronomy. Those he found most interesting

were the last two, and he had thoughts of becoming an astronomer.

Following the custom of students in Germany at that period he did not spend

all his time at Breslau, but migrated for the summer semesters to the University

of Heidelberg in 1902 and the University of Zu¨ rich in 1903, enjoying

to the full the amenities and cultural opportunities of these cities. It was at

Heidelberg that he met James Franck, who was to become a life-long friend

268 From Ehrenfest to Schr ¨ odinger

and later colleague at Go¨ ttingen; at Zu¨ rich that he received his introduction

to advanced mathematics from Hurwitz’ lectures on elliptic functions. By

returning to the university of his native city for the winter semesters and

for most vacations, he was able, at the home of his late father’s friends the

Neissers, to meet many writers and musicians, including such celebrities

as Gerhard Hauptmann, Ferruccio Busoni, Artur Schnabel, Edwin Fischer

and Carl Flesch.

Among Born’s fellow students at Breslau were Otto Toeplitz and Ernst

Hellinger, both of whom were destined to become mathematicians of distinction.

It was they who told him of the three prophets of Go¨ ttingen –

Klein, Hilbert and Minkowski – and inspired him to make the pilgrimage

thither. At the Georgia Augusta he began by attending lectures by Hilbert

and Minkowski. Before long Hilbert offered him the unpaid post of Privatassistent,

his primary duty being to prepare a fair copy of the professor’s

lecture notes. The main attraction was the privilege of close contact with

Hilbert and Minkowski, accompanying them on their rambles in the woods

around Go¨ ttingen, during which they would discuss not only mathematics

but also philosophical, social and political problems. A seminar they conducted

on the electrodynamics of moving bodies directed Born’s attention

to the problems of what was to become known as the special theory of

relativity. Later on he wrote a useful elementary introduction to the theory,

but at that time Einstein’s first paper on relativity had only just appeared.

Minkowski was developing his own four-dimensional formulation of

electrodynamics.

Another seminar that Born attended was one on elasticity, which

Klein conducted jointly with the applied mathematician Runge. Born, who

had offended Klein by irregular attendance at his lecture course, was called

on to give an account of a problem in elastic stability at very short notice

due to a fellow student falling sick. Lacking sufficient time to study the

literature, he treated the subject ab initio; Klein was so impressed by his

performance that, with Born in mind as competitor, he set the problem

for the annual university prize competition. At first Born refused to enter

his name, thus giving fresh offence to ‘the great Felix’, but eventually he

capitulated, submitted his entry and carried off the prize.

When it came to the oral examination for the doctorate, Born deemed

it inadvisable to risk having Klein question him on geometry, which he had

intended offering as one of his subjects, so he offered astronomy instead.

Having already started studying the subject at Breslau, at Go¨ ttingen he

was accepted into the astrophysical seminar of Karl Schwarzchild. Born’s

Max Born (1882–1970) 269

relations with Schwarzchild were happier than they had been with the

formidable Klein, and the doctoral examination in January 1907 passed off

successfully with Schwarzchild as examiner in place of Klein. Born’s thesis

was based on his prize dissertation on elastic stability; for the rest of his

life he retained an affection for his first scientific offspring, through which

he first tasted the joy of independent investigation of a problem and the

satisfaction of finding the predicted results in harmony with experiment.

At Go¨ ttingen Born came into contact with a remarkable group of

younger mathematicians and physicists, not only Hellinger and Toeplitz,

but also Richard Courant, Erhard Schmidt and Constantin Carath´eodory.

Among the subjects he studied were the kinetic theory of gases, electrodynamics

and the aberrations of optical instruments. After taking his doctorate,

Born would normally have had to undergo a year’s compulsory military

service, but a tendency to asthma enabled him to shorten the period. The

experience, he tells us in his autobiography, confirmed his antipathy to

all things military. A visit of six months’ duration to Cambridge followed.

As an ‘advanced student’ at Caius College he attended lectures by Larmor

and Thomson. Larmor’s lectures he found much inferior in content to

Minkowski’s, quite apart from problems with the Irish accent, but Thomson

he found most stimulating.

On returning to Breslau, Born engaged in some experimental work,

but soon turned to theory again. By combining Einstein’s special theory of

relativity with Minkowski’s mathematical foundation, he found a new and

more rigorous way of calculating the electromagnetic mass of the electron,

and sent the manuscript to Minkowski inGo¨ ttingen. As a result, Minkowski

invited him to return to the Georgia Augusta to assist him with his work

on relativity. Sadly, the possibility of this promising collaboration was cut

short by Minkowski’s untimely death. In his autobiography Born relates

how downcast he felt by the ruin of all his hopes and how he again fell foul

of Klein, but managed through the good offices of Runge to convince Hilbert

of the soundness of his ideas. He also attended theoretical and experimental

courses underWoldemar Voigt, who offered Born a position as Privatdozent.

Among his colleagues on the teaching staff at the Georgia Augusta were

Richard Courant, HermannWeyl and von K´arm´an.With the last of these he

developed the Born–K´arm´an theory of the specific heats of solids. This was

the beginning of an ambitious programme of research that was to occupy

Born and his pupils for many years, namely the explanation of the physical

properties of solids – in particular crystals – on the basis of their lattice

structures.

270 From Ehrenfest to Schr ¨ odinger

Although he was still no more than a Privatdozent, an invitation from

Albert Michelson to visit Chicago took Born to the USA for the first time in

1912. The next year Born married Hedwig (n´ee Ehrenburg), the daughter of

the professor of jurisprudence at G¨ ottingen; her forebears included Martin

Luther. Between them, she and her husband could claim an extended family

of great intellectual distinction. They had three spirited and sometimes

turbulent children, Irene, who became a well-known singer, Margaret and

Gustav, who became a prominent biologist.

The outbreak of war in August 1914 coincided with the offer of an

associate professorship at the University of Berlin, where Born would have

Planck as a colleague. Upon arriving in Berlin in the spring of 1915, Born

was soon drawn into the war effort, but not before he had completed the

manuscript of a book on the dynamics of crystal lattices. After a short time

as a radio operator in the German air force, he was seconded to the artillery

with commissioned rank for research on acoustical range-finding. Characteristically,

he conceived it to be his duty to have as many as possible of

his former colleagues and students recalled from the front-line to work in

his section. After the war was over, although conditions in Germany were

extremely difficult, Born was able to appreciate the life of Berlin, particularly

the scientific life. Among the physicists he particularly enjoyed the

friendship of Einstein, with whom he had long been in correspondence but

now could know as a colleague and neighbour. Born was an accomplished

pianist and they often played violin sonatas together.

In 1919 von Laue, at that time professor in Frankfurt, proposed an

exchange of chairs with Born in Berlin in order that he could more easily

work with his beloved teacher Max Planck. The exchange was arranged with

the agreement of both universities, and as a result Born moved to Frankfurt

in April that year as professor and director of the institute of theoretical

physics. Two years later, he moved on to a similar post atGo¨ ttingen. He was

joined by his friend James Franck, who took charge of the experimental side

of physics at the Georgia Augusta. During the early years of this, his third

period in Go¨ ttingen, Born and his students carried on the work on lattice

dynamics. He also wrote a long survey article for Klein’s Encyclopaedia,

later published as a separate book, and edited the collected works of Gauss.

Before long Born’s chief research interest shifted towards quantum

theory, where he was particularly fortunate in having as his junior colleagues

Pauli and Heisenberg. During the winter of 1925/6 Born was in

America again for a lecture tour, including a course on ‘problems of atomic

dynamics’ at the Massachusetts Institute of Technology. This was written

Max Born (1882–1970) 271

up and became the first book to be published on quantum mechanics. Three

years later he visited Russia with a party of European scientists. He had been

feeling the strain of directing the institute in G¨ ottingen, which had become

a place of pilgrimage for large numbers of young theoretical physicists from

all over the world, and, although the Russian tour might have provided a

respite, instead it triggered a nervous breakdown, which forced him to interrupt

his teaching and research for the following year. He maintained that

afterwards he never fully recovered his earlier capacity for intensive work.

Nevertheless, the publication in 1933 of his classic textbook, Principles of

Optics, demonstrated his ability to complete a major undertaking on top of

his other commitments, even in a field that was not central to his interests.

In May of that same year Born, being Jewish, was effectively deprived

of his Go¨ ttingen chair and left Germany. After a short rest in the Italian

Tyrol, where he was consulted by Lindemann, he accepted an invitation

to go to Cambridge and work with Infeld on a non-linear modification of

Maxwell’s electromagnetic theory, which they thought might remove the

difficulty of the infinite self-energy of the electron, but the results could

not be reconciled with quantum theory. For Born, accustomed to directing

a large department, there was a significant problem of adjustment, but he

came to feel, like many other refugees, that it was a rejuvenating experience.

He wrote the well-known textbook Atomic Physics, which went through

numerous editions, and a popular work, The Restless Universe. After

Cambridge he made a visit to the Indian Institute of Sciences in Bangalore,

where it was hoped to recruit some of the displaced German scientists, and

then seriously considered the offer of a more permanent post in Moscow,

but just at this time the Tait Chair of Natural Philosophy at the University

of Edinburgh fell vacant, and in 1936 Born was elected.

In Edinburgh, Born rapidly established a research school on the continental

model, although he was not altogether successful in grafting this

onto the undergraduate teaching in his department. A member of the Born

school around 1940 described what it was like:

The theoretical research was essentially carried out in one large room

in the basement of the physics building (the old infirmary) in

Drummond Street. There was Born’s writing desk and a number of

long tables at which usually about a half-a-dozen research workers

(including myself) sat. When Born arrived in the morning he first used

to make the round of his research students, asking them whether they

had any progress to report and giving them advice, sometimes

272 From Ehrenfest to Schr ¨ odinger

presenting them with sheets of elaborate calculations concerning their

problems which he had done himself the day before. The apparent ease

with which he could switch from one subject to another during this

inspection tour was truly amazing. Being such an incredibly fast

worker himself he could on occasion become quite impatient when he

found that a student had not managed to complete the calculations

which had been suggested to him only the day before. The rest of the

morning was spent by Born in delivering his lectures to undergraduate

honours students, attending to departmental business, and doing

research work on his own. Most of the latter, however, he used to

carry out at home in the afternoons and evenings.

His seventeen-year tenure of the Edinburgh chair afforded Born many opportunities

for visits, sometimes extended, to conferences and universities at

home and abroad, including congresses in Paris, Bordeaux and the Soviet

Union; he also spent a term in Egypt and gave the Wayneflete Lectures in

Oxford. The war years brought little disturbance to his routine of research,

apart from a temporary decline in the number of his research students.

Although he was a master of atomic physics, he did not contribute to the

efforts that went into the development of the atomic bomb. After the war

Born’s research school continued to be active, but, at the end of the session

1952/3, having reached the retirement age of seventy, Born returned to

Germany and settled at a small and secluded spa within easy reach of

Go¨ ttingen. Some amends were made to him for his treatment by the Nazis

by the restoration of his confiscated property and pension rights, and by the

conferment on him (along with Courant and Franck) of honorary citizenship

ofGo¨ ttingen, whose university he had served with such distinction. He

revised several of his books for new editions and wrote his autobiography,

but his scientific career was essentially over. The award of a shared Nobel

prize in physics in 1954, for his research in quantum mechanics, was one of

those cases in which the prize was in recognition of work done long before.

In his later years Born became increasingly active in the cause of the

social responsibility of scientists, and wrote and lectured indefatigably on

what he saw as the appalling dangers inherent in the technological explosion

and the concurrent collapse in ethical standards. In 1957, when the nuclear

policy of the Federal Republic of Germany was a matter of active debate,

Born was one of the leaders of the ‘G¨ ottingen eighteen’ who made public

their belief that nuclear armament was a suicidal policy and declared

that they would refuse categorically to collaborate in any scientific work

Niels Bohr (1885–1962) 273

associated with nuclear weapons; although Born himself was not religious,

he was a staunch pacifist as was his Quaker wife Hedwig. He was a kindly,

even-tempered but rather formal person; he could sometimes become surprisingly

inflexible in matters of scientific controversy. He died in hospital

on January 5, 1970, at the age of eighty-seven, and Hedwig survived him by

only two years.

Niels Bohr (1885–1962)

The first son, Niels Henrik David, of Christian and Ellen Bohr was born

in Copenhagen on October 7, 1885. His older sister Jenny was born two

years earlier and his younger brother Harald two years later. Their mother,

a generous, intelligent and liberal woman, came from the wealthy Jewish

Adler family, which was prominent in Danish banking and parliamentary

circles. Their father was a university professor, a famous physiologist and

lover of science, also the founder of the university football club; although

he too was of Jewish extraction he had been converted to the Lutheran faith.

The three Bohr children were brought up as Christians in a patrician home

of culture where they were exposed to a world of ideas in animated debates

in which conflicting views were examined rationally and in good humour,

274 From Ehrenfest to Schr ¨ odinger

and they developed a respect for all those who seek deeper knowledge and

understanding. It was a close-knit family; the two brothers were inseparable

in childhood and remained close throughout life.

The school career of Niels, the elder brother, was academically successful

without being outstanding. Later, looking back, he stated: ‘my interest

in the study of physics was awakened while I was still at school, largely

owing to the influence of my father’. As well as a growing interest in physics

and mathematics, he early showed an ability to inspire affection in others,

forming friendships at school that were to last throughout his life. For a

glimpse of him as a schoolboy we have some reminiscences by classmates:

‘in those days Niels was tall, rather coarse of limb, and strong as a bear.

He was not afraid to use his strength when it came to blows during the

break between classes. He seemed to be quite an ordinary boy, gifted but not

smug, a promising honours student, but otherwise a young man like the rest

of us.’

It was at the University of Copenhagen that Niels Bohr’s potential

as a scientist was first recognized. In 1907, at the age of twenty, he was

awarded the Gold Medal of the Royal Danish Academy of Sciences and

Letters for a prize exercise on the measurement of surface tension by the

study of vibrating fluid jets. This careful and complete piece of research,

both experimental and theoretical, drew upon and extended the work of

Rayleigh, and served later on to give Bohr particular insight in his liquiddrop

model of the atomic nucleus. Although Bohr worked very hard, he also

played hard, so no account of his life would be complete without mention of

his enthusiasm for sports, especially association football, although he was

not quite up to the standard of his younger brother Harald, who captained the

Danish team at the 1908 Olympic Games. The brothers became nationally

famous for their achievements on the football field; their father had helped

to make soccer the Danish national game.

Both for the master’s degree and for his doctorate, Bohr submitted

studies of the application of electron theory to the explanation of the physical

properties of metals. Although these studies were not without some

success, it was through this work that he began to be aware of the difficulties

and limitations of classical physical theory in the description of electron

behaviour and of the need for some radically different mode of description of

atomic processes. He began to recognize the limitations of ordinary language

in the description of phenomena and the need to accommodate apparently

conflicting aspects in order to form complete descriptions. He was convinced

that ‘there is no point in trying to remove such ambiguities; we

Niels Bohr (1885–1962) 275

must rather recognize their existence and try to live with them’. Such ideas

reappeared later in his principal contribution to physics and epistemology:

the complementarity argument.

Harald Bohr obtained his doctorate two years earlier than his older

brother Niels and went on to become a distinguished mathematician. Their

sister Jenny was also talented; she studied first history at the University of

Copenhagen and then English at the University of Oxford before embarking

on a career in schoolteaching, but later became mentally ill and died at

the age of fifty. Niels was an assiduous correspondent; he left a legacy of

interesting and apparently spontaneous letters: in fact they were far from

spontaneous but, like his scientific papers, only reached their final form

after multiple drafts and painstaking revisions. As early as 1911 he began

enlisting the aid of an amanuensis – at first his mother and, later on, his

sons, his colleagues or his wife.

In 1910 Niels Bohr met his future wife Margrethe Nørlund, the daughter

of a pharmacist, and they soon became engaged. The next year, in the

period before marriage, he made the first of many visits to Britain. In Cambridge

Bohr failed to interest Thomson in the work he had been doing on

the theory of metals, instead Thomson gave Bohr a rather routine research

project to work on. Bohr spent his first few months in England feeling fairly

frustrated until he met and impressed Rutherford, who had recently devised

his new model of the atom. The model was like a miniature solar system,

consisting of a dense, positively charged nucleus with a family of negatively

charged electrons in orbit around it.

In August 1912 Niels and Margrethe were married in the town hall

of Slagelse, where she had been brought up. They took their honeymoon

in Scotland, calling at Cambridge and Manchester en route. Then Bohr,

taking the Rutherford atomic model as a starting-point, began to work out

the ideas on atomic stability that were to lead to the quantum description

of atomic structure. In 1913 he published these ideas in three articles in

the Philosophical Magazine, where he set out his bold attempt to combine

aspects of classical physics with Planck’s concept of the quantum of action,

the potential of which remained largely unexploited. This new theory, in

which the electrons were restricted with regard to the orbits they could use,

yielded impressive quantitative agreement with measurements of atomic

spectra. These three articles, known as the Trilogy, formed the foundation

of Bohr’s early reputation. Although it was not immediately accepted by

everyone, his concept intrigued his contemporaries and made them aware

of the need for a new way of describing events at the atomic level. The

276 From Ehrenfest to Schr ¨ odinger

Bohr atomic model, although it has been superseded scientifically, persists

today in the minds of many people as a vivid image of what atoms look

like.

The association between the exuberant experimenter from New

Zealand and the thoughtful young Danish theoretician developed and deepened

into a kind of father–son relationship during a quarter-century of

friendship and collaboration. In Manchester Bohr found a stimulating atmosphere

and congenial colleagues. It was there, in the spring and early summer

of 1912, during a period of almost continuous research, that he made several

important contributions to atomic physics: he helped to clarify the nature

of radioactive transformation, was probably the first person to recognize the

basis of nuclear isotopy, and developed a theory of the energy loss of alpha

particles as they passed through matter – a topic that interested him all his

life.

During the years leading up to the First World War Bohr held some

fairly junior appointments at the University of Copenhagen. It was during

this period that Courant first met him; he described Bohr as a somewhat

introverted, saintly, extremely friendly yet shy young man. Throughout his

life Bohr spoke with a quiet voice, hardly above a whisper, and listeners

had trouble understanding him in any language. In what he said or wrote he

was always conscious of the many limitations and conditions that restrict

the validity of any statement: as he liked to express it: ‘truth and clarity

are complementary’. He was always concerned about hurting any person’s

feelings. Also he had great difficulty in making definite plans, only too often

changing them almost as soon as they had been arranged.

Bohr spent the early years of the FirstWorldWar in Manchester, working

with Rutherford, while hoping to obtain a more senior post in Copenhagen.

He and Margrethe enjoyed the carefree life of Manchester very much:

‘we have met with so much kindness and feel so much at ease’. Bohr and

Rutherford had much in common scientifically; their collaboration was one

of the most brilliant, fertile and fortunate in the history of science. Both

were capable of enormous enthusiasm for a promising idea in physics. Both

refused to be deflected by unimportant details, although they could give

painstaking attention to detail when it mattered. Both regarded mathematics

as an important tool in formulating and applying the laws of physics,

but never as an end in itself. Rutherford was fond of making disparaging

remarks about theoreticians who were too attached to formal mathematics,

so much so that he is sometimes believed to have been opposed to theory

altogether. Bohr was too polite for such remarks, but restricted himself to

Niels Bohr (1885–1962) 277

the minimum of mathematics in his own work. Both were untidy lecturers

but could fascinate and stimulate an audience.

In 1916 Bohr heard that a new chair in theoretical physics was being

created at his alma mater and that he was expected to become the first

holder. When Rutherford wrote a letter of recommendation for him it was

in no uncertain terms: ‘in my opinion Dr Bohr is one of the most promising

and able of the younger mathematical physicists in Europe today. I think

any university would be fortunate who is able to acquire the services of

such an original and fruitful investigator.’ So in 1916 Bohr returned to his

homeland as the first professor of theoretical physics at the University of

Copenhagen. As soon as the war was over, young physicists began flocking

to the Danish capital, where research could be pursued in an atmosphere

free of politics. Not everyone fell under his spell, however; Einstein, for one,

was too independent-minded and too involved in the theory of relativity.

In 1916 also the Bohrs’ first child, Christian Alfred, was born. Five

more sons followed: Hans Henrik in 1918, Erik in 1919, Aage Niels in 1922,

Ernest David in 1924 and Harald in 1928. Hans, in later life, gave a picture

of the family milieu in which he grew up: ‘father always took an interest in

us and from the beginning tried to teach us something about the things he

himself liked best and thought important . . . the dinner table was generally

a meeting-place at which father was eager to hear what each of us had done,

and to relate what he had been doing himself . . . he was no doubt not a

teacher in the accepted sense of the word, but if you were patient and

listened, a wide and rich perspective opened up . . . he was nearly always

occupied with one problem or another.’

Although he was still only thirty-one years old when he returned to

Copenhagen, Bohr’s subsequent influence was exerted not so much through

his own original research as through the way he inspired others, for whom

he provided an ideal environment for scientific work. He began to delve

into the logical and philosophical foundations of physics. Even his first

papers from Copenhagen are often essays in search of verbal understanding

rather than mathematical analyses of crucial problems. His lecturing style

was a discursive mumble, but with small groups and especially in one-toone

discussions he was unequalled in his enthusiasm, his empathy and his

contagious love for the subject. He wrote many scientific and other papers

in the course of his life, but never a full-scale book.

Bohr found an invaluable assistant in Hendrik Antonie Kramers, a

young physicist who had previously studied with Lorentz and Ehrenfest in

Leiden and first came to Copenhagen as a place where science could be

278 From Ehrenfest to Schr ¨ odinger

pursued in an atmosphere free of politics. The two men worked together,

collaborating not only on scientific papers but also on the planning and

administration of the new university institute of theoretical physics, later

to be named the Niels Bohr Institute. Despite the original name, it was to

undertake experimental as well as theoretical research. Within a very few

years of its opening in 1921, this unpretentious building in the capital city

of a small country was to become one of the best-known centres of physics

in the world. The list of visitors over the next two decades – some of whom

came for a few weeks, some for months or even years – reads like a roll-call of

the founders of quantum mechanics. This intensely interactive enterprise,

constantly changing in membership but always led and shaped by the mind

and personality of Niels Bohr, came to be known as the Copenhagen school

of physics. In his forties, the jovial Bohr became a father-figure to scores of

young physicists from all over the world, who liked to call him the Great

Dane.

In 1918 Bohr had published his paper ‘On the Quantum Theory of

Line Spectra’, which presented a detailed elaboration of the correspondence

principle he had introduced five years earlier. In the skilled hands of Bohr

and Kramers, the principle proved a powerful tool for elucidating the fine

structure of spectra and for predicting spectral intensities, transition probabilities

and selection rules with considerable accuracy; however, it was

never fully understood or much exploited by other physicists. Bohr made

his next major contribution to physics in 1922 through several papers on the

theory of atomic structure and the periodic system of the elements. In

the same year he was awarded the Nobel prize in physics ‘for his services

in the investigation of the structure of atoms and of the radiation emanating

from them’. In his acceptance speech, Bohr surveyed the state of quantum

theory and the progress that had been made in applying it to the problems of

atomic structure, but he took pains to point out the limitations and weaknesses

of the theory. He was more acutely aware of these and more perturbed

by them than were others who had accepted his ideas less critically.

After the Nobel prize, Bohr received honours from academies, universities

and other institutions too numerous to mention. In 1921 Planck wrote

to him about the possibility of moving to Berlin, and Rutherford sounded

him out about possibilities in England. However, Bohr’s attachment to his

homeland was too great; all he was prepared to do was offer to make visits. In

1923 he made his first visit to North America, and, although he concluded

that he would not like to live there, he was happy to make further visits to

the USA and later on take advantage of American philanthropy. Notably the

Niels Bohr (1885–1962) 279

Rockefeller-financed International Education Board was particularly helpful

when he needed more accommodation for visitors to the institute. One

of these visitors was Erwin Schro¨ dinger; according to Werner Heisenberg,

the discussions between Bohr and Schro¨ dinger began already at the

railway station in Copenhagen and were continued each day from

early morning until late at night. Schro¨ dinger stayed at Bohr’s house

and so for this reason alone there could hardly be an interruption in

the conversations. And although Bohr was otherwise most considerate

and amiable in his dealings with people, he now appeared to me

almost as an unrelenting fanatic, who was not prepared to make a

single concession to his partner in discussion or to tolerate the

slightest obscurity. It is hardly possible to convey the intensity of

passion with which the discussions were conducted on both sides, or

the deep-rooted convictions which one could perceive equally in Bohr

and in Schro¨ dinger every spoken sentence . . . so the discussion

continued for many hours throughout the day and night without any

consensus being reached. After a couple of days Schro¨ dinger fell ill,

perhaps as the result of the enormous strain. He had to stay in bed

with a feverish cold. Bohr’s wife Margrethe nursed him and brought

tea and cakes, but Niels Bohr sat by the bedside and spoke earnestly to

Schro¨ dinger; ‘but surely you must realize . . .’

‘No real understanding could be expected’, said Heisenberg, ‘since neither

side was able to offer a complete and coherent interpretation of quantum

mechanics.’

In the years that followed, Bohr continued to publish work in atomic

physics, including one highly controversial paper with Kramers and John

Slater. Although Bohr himself had formulated the first quantization rules for

the emission process of radiation, this paper revealed his continuing disinclination

to accept the concept of the photon.With the arrival of Heisenberg

and Pauli in Copenhagen, Bohr’s role became less that of an initiator in the

progress of quantum physics and more that of a supporter, a mentor and a

penetrating critic of those who were leading the way. His mind returned to

some of the preoccupations of his early years: the physical interpretation

of the mathematical formulations of quantum mechanics, the importance

of seeking to define the boundary between a measuring apparatus and a

measured object, and the place of language in making explicit the outcome

of such measurements. His mature views on these questions were brought

together in the paper ‘The Quantum Postulate and the Recent Development

280 From Ehrenfest to Schr ¨ odinger

of Atomic Theory’, presented at the conference to commemorate the centenary

of Volta’s death held at Como in September 1927. In his presentation,

Bohr spoke of the epistemological problems of quantum mechanics, and

again set out his complementarity argument – the principle which he was

to continue to develop and extend until the end of his life and which he

came to believe was his main contribution to our understanding of nature.

These ideas were soon put to stringent test in the debate with Einstein

at the Solvay conference of 1927, which took place shortly after the Volta

Commemoration. Compared with Bohr, Einstein’s spectrum of scientific

interests was much broader; Bohr concentrated almost entirely on quantum

theory and its ramifications. There was another important difference

between them in that Bohr identified very strongly with his native Denmark

and created a major research school in Copenhagen. Although he never

supervised research students, he was stimulated by the endless stream of

visitors and research workers at the institute.

In 1930 Bohr’s mother Ellen died; he had lost his father long before,

in 1911. Further distress was caused in 1934 when the Bohrs’ first-born son

Christian was drowned when sailing out at sea with his father and some

friends; he was just seventeen years old, not uninterested in science but more

interested in the arts, especially poetry. At Carlsberg, near Copenhagen,

the Carlsberg Foundation owned a beautiful mansion that was given to be

used by ‘an outstanding citizen of Denmark, most prominent in science

or literature or the arts’. In 1931 it was offered to Bohr for the rest of his

life, and the Bohrs moved there the next year from their quarters in the

institute, where they had for many years offered hospitality to physicists

from all over the world. The mansion, which was ideal for entertaining,

became not only a family home for the Bohr’s children and grandchildren,

but also a haven for the many colleagues and visitors who stayed there and

a convivial meeting place for scientists, artists and politicians from all over

the world. The Rutherfords were the first of many guests who enjoyed their

hospitality.

For the next few years Bohr continued to develop his ideas, both in

physics and in epistemology. He published works dealing with the problem

of measurement in quantum electrodynamics; an essay entitled ‘Light and

Life’, explaining how the complementarity principle could be applied to

biology, and a paper entitled ‘Can the Quantum-mechanical Description

of Reality Be Considered Complete?’, a response to the well-known paper

by Einstein, Podolsky and Rosen of the same title. After Bohr and Einstein

first met in 1920, they initiated a series of discussions, which, conducted

Niels Bohr (1885–1962) 281

with mutual pleasure and respect, continued for many years and became

part dialogue, part duel and part crusade. They disagreed on many things,

including causality, the meaning of relativity and the incompleteness of

quantum-mechanical descriptions. For nearly twenty-five years each tried

to convince the other, by ingenious argument and subtle logic. Eventually

Bohr’s interpretation of quantum mechanics became the orthodox view.

During this period Niels and his brother Harald, who was at that

time director of the mathematics institute of the University of Copenhagen

(which had been built alongside the institute for theoretical physics) became

deeply involved with a Danish group that had been formed to offer support

to scientists and other intellectuals who were being forced to flee their

homelands by the racial policies of the Nazi government in Germany. These

two institutes acted as a temporary refuge for many of them, and the brothers

dedicated themselves to finding new posts for those such as Lise Meitner

who had suddenly become stateless and unemployed.

In 1934 Bohr made his first visit to the Soviet Union, where he was

impressed by what he was shown, and in 1937 he made a world tour including

China and Japan as well as Russia. Although they were reluctant to leave

their younger sons, especially after the loss of Christian, his wife Margrethe

generally accompanied him on these longer journeys. Beginning about 1934,

Bohr made his next major contribution through his work in nuclear physics,

his theory of the compound nucleus and his elaboration of the liquid-drop

model. This work reached its climax in 1939 with a paper, written jointly

with John Wheeler, on the theory of nuclear fission, although Bohr continued

to work and publish on these topics well into the 1940s. In 1940

Germany occupied Denmark; at first there was a fiction of self-rule, but

this did not last. The institute continued to function, but Bohr’s own role

changed. As a public figure and a focus of national admiration and pride,

he felt a responsibility to help maintain Danish science and culture under

the prevailing conditions. It was during this period that he was asked to

write the introduction to the book Danish Culture in the Year 1940 – a task

on which he lavished the same care and attention to detail and language as

that which he devoted to his scientific writings.

By August 1943 the position of the Danish Jews had become perilous,

and the following month Hitler ordered that they were all to be rounded up

and deported in two freighters that had docked in Copenhagen. Some were

caught, but the great majority escaped to safety in Sweden in the greatest

mass-rescue operation of the war. Bohr himself left Denmark for Sweden in

this way and spent some time there making sure that the refugees would be

282 From Ehrenfest to Schr ¨ odinger

well treated. However, crossing the Kattegat was for him only the first stage

in a journey to Britain, arranged by the British government. His son Aage,

also a physicist, followed a few days later and went on with him to America.

In London Bohr was briefed on what was then known as the Directorate of

Tube Alloys, the precursor of the Anglo-American Manhattan project to

produce atomic bombs, which came as a revelation to him. He agreed to

work on it, although he remarked later that ‘they did not need my help in

making the atom bomb’.

Once in the USA he ran into security problems because of his firm

belief that the Soviet Union should be made aware of what was going on

at Los Alamos. Although he was scientifically interested in the progress

towards the production of the fission bomb, Bohr turned his attention

almost immediately to the political significance of the project and to the

need for early and clear recognition of the threat it would pose to post-war

stability. According to Oppenheimer, ‘Bohr at Los Alamos was marvellous.

He took a very lively technical interest. But his real function, I think for all

of us, was not a technical one. He made the enterprise seem hopeful, when

many were not free of misgiving . . . His own high hope that the outcome

would be good, that the objectivity, the cooperation, of the scientists would

play a helpful part, we all wanted to believe.’

In the spring of 1944 Bohr returned to London, in the hope of conveying

his concerns to Winston Churchill. With some misgiving Lindemann,

Churchill’s scientific adviser, arranged for Bohr to meet the Prime Minister,

but Bohr never succeeded in getting his message across. He was more successful

later when, on his return to America, he had an audience with

President Roosevelt, who was impressed by him at the time but afterwards

had second thoughts. A few months later, after Churchill and Roosevelt

had met privately at the latter’s Hyde Park estate in the Hudson Valley,

Churchill sent a note to Lindemann: ‘the President and I are much worried

about Professor Bohr. How did he come into this business? He is a great

advocate of publicity. He says that he is in close correspondence with a

Russian professor [Kapitza], an old friend of his in Russia, to whom he had

written about the matter and may be writing still. The Russian professor

has urged him to go to Russia in order to discuss matters. What is all this

about? It seems to me that Bohr ought to be confined or at any rate made to

see that he is very near the edge of mortal crimes . . . I do not like it at all.’

In August 1945, a few days after the bombing of Hiroshima, the editorial

page of The Times newspaper carried an influential article by Bohr

entitled ‘Energy from the Atom’, including the following passage:

Niels Bohr (1885–1962) 283

The formidable power of destruction which has come within reach of

man may become a mortal menace unless human society can adjust

itself to the exigencies of the situation. Civilisation is presented with

a challenge more serious perhaps than ever before . . . we have reached

the stage where the degree of security offered to the citizens of a

nation by collective defence measures is entirely insufficient . . . no

control can be effective without free access to full scientific

information and the granting of the opportunity of international

supervision of all undertakings which, unless regulated, might become

a source of disaster . . . the contribution which an agreement about

this vital matter would make . . . can hardly be exaggerated.

In the autumn of 1945 Bohr returned to Copenhagen and once again

took up his role as honoured teacher and stimulating friend of a new generation

of physicists. He devoted much time and thought to promoting a sane

and realistic policy for nuclear armaments and, in 1950, in an open letter to

the United Nations, he made a heartfelt plea for world cooperation. He and

Kramers, who had succeeded Ehrenfest at Leiden and was then chairman of

a United Nations committee on nuclear policy, both worked for peace, but

their efforts were overtaken by events and Bohr’s proposal for openness and

free exchange of information was never tried out.

In Denmark Bohr had become a much respected elder statesman and

was called upon to guide the government’s policy on atomic energy. For

the next ten years much of his time was given to the detailed planning

and completion of the research establishment of the Danish Atomic Energy

commission at Risø. He lent his support to the plan for the establishment

of a centre for European cooperation in science. In the early and delicate

days of the organization, the division of theoretical physics was housed

and grew strong in Copenhagen before moving to Geneva and becoming

CERN. In 1955 he reached the mandatory retirement age for a university

professor and was succeeded in his chair by his Nobel laureate son Aage;

but he continued as director of the institute. Two years before he had lost

his brother and closest confidante, the mathematician Harald.

At the beginning of the 1960s, Bohr and his colleagues began to plan for

a meeting in 1963 to celebrate the fiftieth anniversary of the publication of

the original research on atomic structure. They hoped to renew the intimate

atmosphere of the interwar Copenhagen meetings by inviting back members

of the institute from those years and giving them the opportunity to review

the past half-century of progress and to speculate about what the future

284 From Ehrenfest to Schr ¨ odinger

might hold. However, before this could happen Niels Bohr died suddenly

in his seventy-seventh year at his home in Carlsberg, on the afternoon of

November 18, 1962; the cause was given as heart failure. Nevertheless,

the planned reunion was held, and many of the surviving members of the

Copenhagen School returned to exchange their latest opinions and ideas, as

he would have wished. Afterwards, at the invitation of Margrethe Bohr and

her sons, they gathered once more in the beautiful mansion which they had

come to know so well. She survived him by twenty-two years.

Frederick Lindemann (Lord Cherwell) (1886–1957)

The arrival in the world of Frederick Alexander Lindemann on April 5, 1886

at the German spa of Baden-Baden provided him with a life-long grievance

against his parents, since a German birth-place caused much annoyance

to someone who became in so many ways a member of the British establishment.

His mother Olga, a forceful and handsome American, was born in

New London, Connecticut, in 1851; her British-born father was a successful

civil engineer. She was the widow of a wealthy banker and had three children,

two girls and a boy, when she married Adolphus Frederick Lindemann,

by whom she had four more children, three boys and a girl. The Lindemanns

were Catholics from Langenberg in Alsace. He was a clever man who made

Frederick Lindemann (Lord Cherwell) (1886–1957) 285

a fortune as an entrepreneur concerned with the making and laying of the

early Atlantic cables and with the construction of waterworks in Bavaria.

After the Franco-Prussian war, he settled in England, became naturalized

and remained there for the rest of his life.

All three Lindemann sons were gifted. Charles, the eldest, was a physicist

whose early promise was comparable to that of his brother Frederick,

but who gave up science for a military career; later he led a life of wealth

and ease in the upper ranks of society. The youngest son, James Septimus,

turned into a devil-may-care spendthrift who resided in a villa on the French

Riviera, overlooking the harbour at Villefranche. He was an excellent linguist

of irresistible charm, an habitu´e of the Paris nightclubs and a sore trial

to his brothers; Frederick, who thoroughly disapproved of him, was amazed

when he heard that his wastrel brother had been a British agent in occupied

France during the Second World War. Their sister married twice. Her first

husband was killed in the First World War; her second was so disapproved

of by Frederick that he had little further to do with her.

The family lived in ‘Sidholme’, a large Victorian mansion in the town

of Sidmouth on the Devonshire coast; this belonged to their mother, having

been bought by her first husband, and was sold when she died in 1927; there

was considerable ill-feeling about this at the time. To the house, built in

1826 by the Earl of Buckingham, had been added a well-equipped scientific

laboratory and an observatory, for their father had a serious interest

in astronomy. There was music and tennis and much else to amuse and

instruct the children, whose early education was entrusted to tutors.

Frederick first went to school at the age of thirteen. The school, of no great

distinction, was run by a friend of his father’s. It specialized in preparing

boys for a career in the army; since it was situated in the Scottish Highlands,

Frederick was expected to wear a kilt, which he hated. He learned to play

golf, but later gave it up because he believed that it was bad for his tennis,

the game at which he excelled. He already showed striking mathematical

ability and an extraordinary gift for lightning calculation. Throughout his

life he could recite huge quantities of figures, entirely without interest,

just for amusement. From an early age he had an aversion for black people

amounting to phobia; he attributed this to a particular doll he had been

given in his infancy.

After three years in Scotland, his parents decided that Frederick should

continue his education in Germany, specifically in Darmstadt, the seat of

the Grand Duke Ernst Ludwig, a grandson of Queen Victoria. He began

at the admirable Lyceum and then went on, at the age of eighteen, to the

286 From Ehrenfest to Schr ¨ odinger

Technische Hochschule, where he was joined by his brother Charles. The

Grand Duke took an interest in the young Lindemanns, encouraging them in

the game of tennis, of which Frederick became an exceptionally fine player.

For some reason the brothers challenged another man to a duel, not just the

ritual exercise popular among young Germans but a serious contest with

loaded pistols: fortunately their opponent apologised when he realized that

they were in earnest.

After Darmstadt the brothers moved to Berlin, where Frederick took

his Ph.D. under Nernst in 1910. It was an exciting time, when Planck and

Einstein were creating the new physics. Observing the shy genius of Einstein

at close quarters, Lindemann concluded that the towering intellect was

combined with a pathetic naivety in the ordinary affairs of life. When the

brothers first came to Berlin they brought with them a cook-housekeeper to

run their bachelor establishment, where young ladies were often entertained

and spent the night, but later they moved to the luxurious Adlon Hotel. One

of Lindemann’s fellow students recalled, perhaps a little inaccurately:

I worked in Professor Nernst’s laboratory in the Bunsenstrasse when

Lindemann was there. He was recognized then as the most

distinguished of the researchers working for the Ph.D. He had good

ideas in physics; he was a good mathematician as well as a good

experimenter. He also had a flair for designing instruments. We all

started work like good little boys at 9 a.m. Lindemann rarely appeared

before noon, and rarely stayed after four but he was known to be a

great night worker. He was always well-dressed, often in morning

coat. No-one ever saw him with his coat off working, so to speak at

the bench; he directed others in his research. He was then very thin, a

tall maypole of a man with dark shiny hair. He spoke German softly in

a thin voice with an English accent. Most of us lived in cheap ‘digs’ in

Charlottenberg, ten miles away. Lindemann lived in one or other of

the hotels in Unter den Linden, less than a quarter-mile away. His

staying at the Adlon hotel there impressed the German element in the

laboratory enormously. He kept aloof from the English and American

group in the laboratory as well as from the German but without giving

offence. He was always pleasant and helpful when approached but

never joined in any extra-laboratory activity. Then as later he was

self-indulgent over food, patronising the best restaurants in the Unter

den Linden where the staff knew that although he was extremely

particular about his meals he liked to have exactly the same thing

Frederick Lindemann (Lord Cherwell) (1886–1957) 287

served, day after day. He had acquired these peculiarities as a small

child from his mother; during wartime when food supplies became

scarce these self-imposed restrictions may have damaged his health.

On reading this, his brother Charles remarked that Frederick never

wore a morning coat except on formal occasions. As for the Adlon hotel,

he had been brought up in an atmosphere of wealth and comfortable living,

and throughout his life rarely got to work before lunch-time. Nernst gave

formal dinner parties: on one occasion the Germans present claimed that

they knew Shakespeare better than did the English, to which Lindemann

retorted that the English knew Goethe better than did the Germans, reciting

a few lines of verse that he had just made up to illustrate the point. Another

colleague was struck by his skill in glass-blowing, which in Germany was

left to technicians.

The research which went into his thesis was published in a joint paper

with Nernst. It provided an effective test of the theory which Einstein had

developed for describing how the amount of energy stored in a solid would

increase with increasing temperature. The Lindemann–Nernst theory to

account for this was soon superseded, but at this time quantum theory was

still in a state of flux. In 1911 a signal honour was paid to him when he was

invited with his friend the duc de Broglie (Maurice, not Louis) to act as cosecretary

to the Solvay conference in Brussels. Throughout the conference

he impressed the eminent participants, the leading physicists of the time,

with his ability. Then in 1913 he was invited by Millikan to give a graduate

course at the University of Chicago. He accepted and lectured on kinetic

theories.

After Lindemann had returned from America, just before the beginning

of the FirstWorldWar, he joined the Royal Aircraft Factory at Farnborough.

This unique institution had evolved from an establishment concerned

with the military use of balloons but by this time was studying the new science

of aerodynamics. Those who worked there were remarkable people. By

a process of improvization that has since become legendary, they were to

design and construct aeroplanes capable of remaining in the air for hours at

a time and to devise the instruments by means of which they were navigated

and controlled. Lindemann believed that the scientists at Farnborough

ought to know how to fly. Despite his poor eyesight, he gained a pilot’s

certificate, after minimal training, and was able to put his ideas about flight

to the test. He was accustomed to enter and leave his plane with bowler hat

and umbrella. Because of his birth-place the ground staff firmly believed

288 From Ehrenfest to Schr ¨ odinger

that he was German and would not allow him enough fuel to fly across the

English Channel.

In the early days of aviation, an aircraft that went into a tailspin was

generally doomed. Lindemann worked out a theoretical solution to the problem

and was determined to try it out in practice. He did so successfully,

although there is some doubt as to whether he was the first to do so. In his

own words:

in 1916 many pilots were killed flying our recently designed planes by

spinning into the ground. Although various people had succeeded in

getting out of a spin, nobody quite knew how, nor indeed how or why

aircraft spun at all. Anyone watching a spinning plane could see that

the rate of turn did not increase on the way down. I concluded

therefore that the lift on both wings must be equal; and this could

only be true – since the outer wing is beating against the air whereas

the inner is not – if its effective angle of incidence was on the high side

of the angle of maximum lift, whereas for the inner wing it was the

other way round. This being so, if the speed were increased the

aeroplane would no longer spin. Experiments proved this idea was

correct . . . therefore pilots were taught to push the stick forward – the

very opposite of the instinctive reaction of pulling back in order to get

the nose up – and to straighten out the rudder and then pull out of the

dive in the ordinary way.

This was by no means his only contribution to the war effort. For

example, he also designed a bomb sight and, characteristically, demonstrated

it himself. At the end of the war he could look back on his work

at Farnborough with satisfaction. His foreign education ended, the love of

England which had been nourished in boyhood by the hills and lanes of

Devonshire, and which was to burn with so fierce a flame for the rest of his

life, now possessed him, becoming the focus of his loyalty and devotion.

The study of physics in Oxford, or experimental philosophy as it was

then called, began in 1749; by 1860 there was a professorship in the subject.

Lindemann was elected to this in 1919 and as a result became head of

the Clarendon Laboratory, then in something of a decline. The chair was

attached toWadham College, where he became a fellow and member of the

governing body, but the set of rooms he was offered there was unmodernized,

without even a bathroom and lavatory, and his offer to install these at his

own expense was turned down. Before long he migrated to Christ Church,

the college which had endowed his professorship, where he became a

Frederick Lindemann (Lord Cherwell) (1886–1957) 289

Student (i.e. Fellow) and was provided with a more comfortable set of rooms.

He was not a member of the Christ Church governing body, but regularly

attended the one at Wadham, which he helped to turn into a college noted

for science.

Lindemann was already generally known as ‘the Prof’, although his

earlier nickname of ‘Peach’ lingered on. As a lecturer he was not a success,

because he spoke in such a low voice that he was difficult to hear. Already he

had many enemies, who thought of him as a once-great physicist who had

deserted the profession in which he had been trained and for which he was

so eminently gifted. Yet, despite being a wealthy man, he was determined

to continue his scientific career; if he had not secured the Oxford post he

intended to try for one in America. He was elected a fellow of the Royal

Society in 1920, at the early age of thirty-three.

At Oxford a great deal of his time and energy was expended on building

up the Clarendon Laboratory to one comparable with the Cavendish

at Cambridge. The peculiar history of the Clarendon was as follows. The

first earl of Clarendon was a great Restoration statesman and historian, the

author of a history of the Civil War. In 1751 his grandson, Lord Cornbury,

left some of the first earl’s papers to trustees, with the direction that the

money derived from their sale or publication should be used for the benefit

of the University of Oxford. After other proposals had been considered

and rejected, including one for a riding school and another for a swimming

pool, the trustees had been persuaded that it was high time that there was

a laboratory for physical science.

The Clarendon Laboratory was built from the funds available and

opened its doors in 1872. It was the first purpose-built physics laboratory at

an English university and its design gave it a curiously ecclesiastical appearance.

In 1900 a new professorship, called theWykeham because it was partly

funded by New College, was established in physics; and ten years later an

electrical laboratory was built. The arrangement was that the professor of

experimental philosophy, at the Clarendon, would take responsibility for

mechanics, heat, light and sound, while the professor of physics, at the new

laboratory, would take responsibility for electricity and magnetism. The

separation of responsibility for experimental physics between two laboratories

and heads of department led to bitter rivalries, which lasted until the

laboratories were merged in 1945.

When Lindemann was appointed he was unaccustomed to the peculiarities

of Oxford. His predecessor had been entirely opposed to research;

there was no staff at the Clarendon and hardly any apparatus for carrying out

290 From Ehrenfest to Schr ¨ odinger

experiments, except for an extravagant provision of the best obtainable optical

apparatus. The laboratory was badly in need of modernization; the water

supply was inadequate, for example, and there was no electricity supply at

all. When Lindemann took over, his first task was to change this deplorable

state of affairs. It says much for his perseverance, his skill in choosing men

and his political ability, and perhaps not a little for the broad-mindedness of

Oxford, that, long before he retired, the New Clarendon Laboratory which

he had persuaded the university to build was comparable in importance to

any department of physics in England. However, he did not achieve this in

the normal way by setting up a school based on his own particular line of

work and achieving pre-eminence in it. Being wealthy himself, he was good

at raising money for his laboratory; and he had his own way of finding talented

staff, as we shall see. His friend Max Born has given us some insight

into his character:

I have often pondered what feature of his character prohibited this

versatile mind from producing a great new concept of physics,

comparable with the quantum of action. Planck stuck to classical

concepts as long as possible, but when he had convinced himself that

the facts of observation could not be explained in the frame of

classical theory he was just as decided to develop new and strange

ideas. He was a revolutionary not by character but through his

willingness to acknowledge the power of evidence. Lindemann,

although conservative in many respects, had a natural revolutionary

strain which found its outlet in physical theory. He had little respect

for traditional thinking and as soon as some new facts appeared not to

fit in within current theory he jumped to conclusions about

fundamental assumptions without analysing the evidence in detail.

His occupation with other things, the administration of his laboratory,

university affairs and politics, allowed him little time for following up

his ideas and for looking in the physical literature for confirmation.

Lindemann, who was not himself Jewish, appeared mildly anti-

Semitic at times, but he was a key figure in the efforts made to rescue

Jewish scientists from the Nazis. Although he had no love for the Jews as

such, he deplored the way they were being treated in Germany. The kindness

Lindemann showed towards Jewish ´emigr´es, and the fact that he became a

close personal friend of some of them, shows that his superficially hostile

attitude towards Jews was never a deep one. He was one of the first to realize

that, owing to the folly and brutality of Hitler, these brilliant and highly

Frederick Lindemann (Lord Cherwell) (1886–1957) 291

trained men and women were now available to work in Britain. He wasted

no time, going at once to Germany to visit them with a view to inviting

some of them to continue their research work in his laboratory; there was,

he thought, room for at least six of them to continue their work at Oxford

and to assist in the development of the Clarendon. He persuaded Imperial

Chemical Industries to provide thirteen two-year grants for Jewish refugees.

Other firms began to follow this lead, so that there were funds to pay their

salaries.

To return to Max Born’s reminiscences:

In the spring of 1933 I was compelled to leave Germany as a

consequence of Hitler’s accession to power. We spent the summer in

Selva, Val Gardena, South Tyrol, and here Lindemann appeared with

his car and chauffeur, to discuss the political situation with me, in

particular the fate of the numerous scientists who lost their position

in Germany. He explained to me his plan to improve the situation of

science in Oxford by inviting refugee physicists to the Clarendon

Laboratory. I was not available for the project because Cambridge had

already offered me a post. But I was deeply impressed by Lindemann’s

idea which was not only generous to the homeless scientists but

clever and far-sighted in regard to the future of Oxford.

‘He did not shrink from travelling far and wide through Europe to achieve

his aim, and thus he found me in Selva’, Born continued, ‘it is known how he

made the Clarendon one of the centres of physics in Great Britain by recruiting

Simon and his group, Kurti, Mendelssohn, Kuhn and others, providing

them with decent positions, excellent working conditions and – last but not

least – encouraging them through a deep understanding of their projects –

although he practically gave up physical research he was always amazingly

up-to-date, not only about the work done in the Clarendon, but elsewhere

in the world.’

Lindemann’s initiative in securing the German scientists was sometimes

wrongly attributed to a selfish desire to increase the prestige of Oxford

science and his own Clarendon Laboratory in particular. In fact, he did

excellent work in placing distinguished German Jewish scientists in other

English universities besides Oxford and in obtaining funding where necessary.

He insisted that the object was not philanthropy but the promotion of

scientific research in Britain.

Sir Cyril Hinshelwood, sometime president of the Royal Society,

summed up Lindemann’s scientific work in the interwar years as follows:

292 From Ehrenfest to Schr ¨ odinger

Before he came to Oxford Lindemann’s most important contribution

had on the whole been theoretical rather than experimental, he was

one of the most brilliant analytical minds I have ever known, and he

continued throughout life to take a deep interest in the fundamentals

of science. His views on all matters of theory were always worth

hearing. He was always interested in the work of others, and although

his criticism at times tended to be destructive, he was always fertile in

suggestions about interpretations which at their best could be

intensely illuminating.

He had been a brilliant young man moving in the most

distinguished European scientific circles, and he came, still young,

into a university where science was still looked down upon by the

dominant schools. He found himself playing two very important and

stimulating roles. On the one hand he was something of an oracle in

scientific circles, and, on the other hand, he began the rehabilitation of

science among those people who were forced to respect his brilliance

of mind and to recognize in this rather glamorous continental figure

someone very different from the image they liked to make of the man

of science. Add to this Lindemann’s charm and mondain predeliction,

and it is hard not to see him devoting a great deal of his energy to the

playing of a kind of Socratic role.

As far as physics (and chemistry) went this was by no means a

dereliction because his analysis often was of the greatest help to other

people, and I would say that he made a great and real contribution to

the modern rise of scientific studies in Oxford. He continued to think

deeply about the major problems of his subject. He did not solve them;

they have not been solved yet. And we must bear in mind that

[Lindemann] was someone who would have scorned to publish

anything in the nature of a pot-boiler, even to use that word in its least

pejorative sense. He stimulated many things for which he never

claimed credit . . . Some people have said that he preferred social

success to science . . . he preferred it to anything but the finest vintage

of science, and because it was not given to him to solve the deepest

problems he was not much interested in the lesser things. Perhaps to

all this one must add a certain element of indolence.

At Christ Church it was a long time before Lindemann gained general

acceptance in the Senior Common Room. He assailed the philosophers with

instinctive relish and loved to tease the historians with questions about

Frederick Lindemann (Lord Cherwell) (1886–1957) 293

events of which he had expert knowledge but they did not. In the last twelve

years of his life he had become a character, the most popular member of

the Room, whose appearances were eagerly awaited. As one of his friends

wrote:

If we had some interesting guest dining, our eyes strayed over to the

door at about 9.15 hoping that he would appear and add new life to our

party. We were usually not disappointed. The door opened slowly and

his well-known figure appeared. He walked with measured tread, for

he was already ailing. He took off the heavy greatcoat, and placed it

methodically on the table and the bowler hat on top of it. Then he

came forward to join us, ready and anxious to be interested in the

affairs of whoever was there, attentive, quite unassuming, and full of

jests and anecdotes appropriate to the person. Or if there was no-one

who especially wanted to talk to him, and a bridge table was out, he

liked to stand behind and watch the game. He knew all about it but

very rarely interjected a comment. Over and over again we tried to

persuade him to play himself, but he declined to do so on the ground

that, if he made a mistake, that would cause him to lie awake all night

replaying the hand.

His college rooms were on the first floor of Meadow Buildings. Outside

his windows the flat tranquil meadow stretched down to the river, where

the painted barges then lined the bank. His set consisted of a sitting room,

dining room and bedroom, and a spare room; he had installed a bathroom and

lavatory. Although he lived in great comfort, he had little taste. His personal

needs were attended to by his factotum Harvey, or Harvey’s assistant, and his

cars were normally driven by a chauffeur. When forced to take the wheel

himself, he did so reluctantly and was an execrable driver, at once timid

and dangerous, and in a state of sustained tension that made him abusive

to other motorists. On the continent, he travelled in patrician comfort, his

progress resembling that of some English milord in the eighteenth century.

He loathed the English winter and usually managed to escape to somewhere

warmer.

Lindemann was a welcome guest at many of the grand houses of

England and as remote from the proletariat as an aristocrat of the French

ancien r ´egime. He was frequently at Blenheim Palace, the seat of the duke of

Marlborough and conveniently near Oxford. Blenheim was the birth-place

ofWinston Churchill, whom Lindemann had first met at the end of the First

World War. He became better acquainted with Churchill in 1932, when he

294 From Ehrenfest to Schr ¨ odinger

accompanied him with others to follow the route of Marlborough’s famous

march from the Netherlands to the Danube, and then three years later when

he joined Churchill on a cruise along the east coast of Spain to Tangier. Later

they became close friends.

Long before most people, Lindemann foresaw the coming war. He

made a vain attempt in September 1933 to meet the dictators Hitler and

Mussolini. He stood for Parliament as a university member in 1935, but

was not elected. He was one of the minority pressing for Britain to rearm

and particularly to strengthen its defences against air attack, but there were

different views regarding what, if anything, should be done A major feud

developed between Lindemann, backed by Churchill, and Tizard, a scientific

czar who was more influential with the service chiefs. Both scientists

had studied with Nernst and worked at Farnborough. From being a strong

supporter of Lindemann, whom he thought the cleverest man he had ever

known, as clever as Rutherford, Tizard turned against him. The abilities of

both scientists and their former friendship made the pettiness with which

they conducted their feud depressing to everyone else; there were faults on

both sides, but it was one of those situations in which Lindemann’s German

birth was held against him. In 1937 he stood for Parliament again in a byelection

but was not elected. At the outbreak of the Second World War

Lindemann entered public life at a high level when Churchill, as First Lord of

the Admiralty, appointed him his personal adviser; his role was primarily but

not exclusively a scientific one. When Churchill became Prime Minister,

he continued in the role, and in 1941 he was raised to the peerage; he chose

for his title the name of Cherwell, the tributary which joins the river Thames

at Oxford.

The next year he was appointed to membership of the Privy Council

and given a seat in the cabinet as Paymaster-General, an office with no

specific duties. After the crushing defeat of the Conservative Party in the

general election of 1945, Cherwell, as we should now call him, returned to

Christ Church with relief. However, Churchill asked him to continue as a

member of the shadow cabinet, and in the House of Lords he often spoke

about economic and scientific affairs. Like his scientific lectures at Oxford,

his speeches were generally inaudible, but they could be read afterwards. At

the Clarendon, which he had done so much to build up, he was still titular

head but not greatly involved in its activities. In 1951, when Churchill

became Prime Minister once more, the reluctant Cherwell was persuaded

to take office again and to base himself next door to 10 Downing Street so as

to be within call. However, like Churchill himself, he was past his prime,

Erwin Schr ¨ odinger (1887–1961) 295

and his influence was waning. In 1953 he was made a Companion of Honour

and three years later elevated to a viscountcy.

Cherwell, at the age of seventy, suffered from mild heart trouble and

from diabetes, which was not ameliorated by the peculiar dietary regime

he followed, but otherwise he enjoyed reasonably good health. However,

on July 2, 1957 he had a heart attack and early on the following day he

died from a coronary thrombosis in his college rooms. The funeral service

was held in the cathedral; among those present was the estranged sister

he had not spoken to for forty years. Being tall and saturnine, he would

have made an arresting figure in any society. Owing to his sardonic manner,

the first impression Cherwell made was often unfavourable. This was partly

the result of a caustic tongue and too sharp an understanding of the weaknesses

of others. People were black or white to him; no greys were allowed.

In a sense he was a lonely man, but there was no sign that this was distasteful

to him.

Erwin Schro¨ dinger (1887–1961)

Lindemann’s efforts to recruit scientists who wanted to leave Nazi Germany

did not always meet with success. The case of Erwin Schro¨ dinger is in many

respects unique. The only child of Rudolf and Georgine Schro¨ dinger, he was

296 From Ehrenfest to Schr ¨ odinger

born in Vienna on August 12, 1887. The families of both parents had lived

in the city for three or four generations. His mother, whose maiden name

was Bauer, was the daughter of an able analytical chemist, who became

professor of general chemistry at the polytechnic. Erwin’s father Rudolf,

whose family had originally been Bavarian, had studied under the maternal

grandfather before inheriting a small but profitable business manufacturing

linoleum and oilcloth, which he carried on without much ability or enthusiasm,

preferring to spend his time painting. After a sheltered upbringing,

Erwin’s cheerful and undemanding mother, sickly by nature, became rather

helpless in the face of life’s problems. As for his father, Erwin later described

him as a man of broad culture, a friend, teacher and inexhaustible partner in

conversation, to whom he was always grateful for giving him a comfortable

upbringing and a good education.

The boy entered the akademisches Gymnasium in the autumn of

1898, having just turned eleven, and, after the usual course of humanistic

studies, including a little mathematics, matriculated at the University of

Vienna in the autumn of 1906, bringing with him from school the reputation

of being an outstanding student. Although he did not keep himself aloof,

all the other students regarded him as something special. Later opinion was

divided between those who considered him to be a person of the most amazing

modesty and those (the majority) who thought that he was one of the

most conceited men they had ever met. The main focus of his interests was

the course in theoretical physics given by Friedrich Haseno¨ hrl, the successor

of Boltzmann, who was youthful, full of energy and a brilliant lecturer.

Haseno¨ hrl lectured neither from notes nor from memory, but simply relied

on the strong logic of the science and developed it as he went along. He

often invited groups of students to his house, where his beautiful wife Ella

presided. He was an able mountaineer and expert at skiing and other winter

sports.

Schro¨ dinger became a Privatdozent in 1910 and the next year, after

performing the obligatory military service, he was appointed to an assistantship

in experimental physics, in charge of the large practical class for

freshmen. He discovered that he was not cut out to be an experimentalist

and in any case the university was not properly equipped for experimental

work. Nevertheless, he had no regrets about the experience. At this time

there were few good academic opportunities in Austrian physics. There

were more in Germany, but, as Schro¨ dinger fully realized, applicants must

already have achieved something quite special; standards were higher than

in Austria.

Erwin Schr ¨ odinger (1887–1961) 297

The theoretical papers he submitted to his Habilitation committee

were one on the kinetic theory of magnetism and another on the kinetics

of dielectrics. Although the work was accepted, with some dissent, he was

allowed to proceed to the final stage by giving a lecture on the magnetron.

Although he had cleared the first hurdle, Schro¨ dinger’s prospects of an academic

career were not good, so he could not afford to get married. He had a

serious affair with the daughter Felicie of some friends of his parents named

Kraus, but her parents were opposed to the match, perhaps because he was

not of the right social standing. After this rebuff he tended to have affairs

with women of a lower social class.

There was an important international scientific congress in Vienna

in 1913, the eighty-fifth meeting of German scientists and physicians, with

over 7000 participants, at which Einstein, already widely recognized as a

great theoretical physicist, lectured on ‘The present status of the problem of

gravitation’. Schr ¨ odinger was deeply impressed and, like Einstein himself,

became attracted by the idea of finding a unified field theory, including

both electromagnetic theory and gravitation. The next year he sent to the

Annalen der Physik the most significant of his early publications, ‘On the

Dynamics of Elastically Coupled Point Systems’, which harks back to one of

the persistent themes in the scientific work of Boltzmann. In this paper

we encounter for the first time the authentic Schro¨ dinger style, with its

urbane confidence and its ability to relate the question in hand to deeper

philosophical concerns of mathematical physics.

Schr ¨ odinger began his career in physics during the last peaceful years

of the Danubian monarchy; the question was not whether but when it would

disintegrate. At the beginning of the conflict which soon turned into the

First World War he was called up for active service. He first learned of

Einstein’s general theory of relativity when he was stationed at the front

and recognized its great importance at once. In the field he was unable to

keep up with the scientific literature, but in the spring of 1917 he was transferred

to Vienna and able to start scientific work again. Active service had

not dulled his theoretical skills, but neither had it led to an outburst of

original thinking about the deepest problems of physics.

After the armistice in 1918 and the disintegration of the empire, conditions

in Vienna became appalling. However, Schro¨ dinger was appointed

assistant at the University of Jena and this enabled him to get married.

His bride Annemarie Bertel was twenty-three, while he was thirty-two. Her

fervent admiration of everything about her husband was one of her great

attractions for him; she had little education and was no intellectual. He

298 From Ehrenfest to Schr ¨ odinger

treated her as a sort of superior domestic servant, whose main function was

to provide him with a comfortable home. There were no children to the

marriage. After his interest in her as a sexual partner had disappeared, they

remained friends and she even helped him to find other women, while she

became interested in other men.

The Schro¨ dingers arrived in Jena, a pleasant German city of about

70 000 inhabitants, and received a warm welcome. The university, founded

in the mid-sixteenth century, had gained a reputation for scientific research,

thanks largely to the presence of the large Zeiss optical works nearby. He

gave his inaugural lecture on recent developments in atomic theory and

made such a favourable impression that he was promoted to associate professor

almost at once. However, the post was not permanent and, when the

opportunity to move to the Technische Hochschule of Stuttgart as an associate

professor with tenure arose, he did so. During their Stuttgart period his

mother died of breast cancer; due to hyperinflation she had become almost

destitute after his father died at the end of 1919.

Although Schro¨ dinger had been passed over for full professorships

in Austria, offers arrived from major German universities, and of these he

chose Breslau. Thus the Schro¨ dingers made their third move in eighteen

months. A few months later they moved again, this time to the University

of Zu¨ rich. At the age of thirty-four he had achieved a full professorship at

a leading university, despite the fact that he had not yet accomplished a

truly outstanding piece of work in any particular field. Neutral Switzerland

had been spared the ravages of war, and living conditions were much better

than in Austria or Germany, although there was high unemployment and

general economic depression. Almost as soon as he had arrived Schr ¨ odinger

was diagnosed with suspected tuberculosis and sent to an alpine sanatorium

in Arosa to recover. It was there that, stimulated byWeyl’s influential book

Raum–Zeit–Materie (Space, Time and Matter), he wrote one of his most

important papers, ‘On a Remarkable Property of the Quantized Orbits of an

Electron’.

When he finally took up his professorial duties, Schro¨ dinger found

that he had a heavy work-load. A student who attended one of his lectures

at this period recalled that it was

extremely stimulating and impressive. At the beginning he stated the

subject and then gave a review of how one had to approach it, and then

he started exposing the basis in mathematical terms and developed it

in front of our eyes. Sometimes he would stop and with a shy smile

Erwin Schr ¨ odinger (1887–1961) 299

confess that he had missed a bifurcation in his mathematical

development, turn back to the critical point and start all over again.

This was fascinating to watch and we all learned a great deal by

following his calculations, which he developed without ever looking

at his own notes, except at the end, when he compared his work on

the blackboard with his notes and said ‘this is correct’. In summertime

when it was warm enough we went to the bathing beach on the Lake

of Zu¨ rich, sat with our own notes on the grass and watched this lean

man in bathing trunks writing his calculations before us on an

improvised blackboard which we had brought along. At that time few

people came to the bathing beach in the morning and those that did

watched us from a discreet distance and wondered what that man was

writing on the blackboard!

While Schr ¨ odinger’s physical health was returning to normal, emotionally

it was a difficult time. He and Annemarie were having problems

with their marriage, which was at a high point of disagreement and tension,

with constant talk of divorce. However, for his work in theoretical physics,

1925 proved to be a marvellous year. Schro¨ dinger was by now particularly

concerned with fundamental problems in atomic physics and quantum

theory, especially the nature of radiation and how it interacts with electrons

and atoms. These new interests brought him into closer relation with work

in progress in the schools of Born in Go¨ ttingen, Sommerfeld in Munich and

especially Bohr in Copenhagen, all of whom had close connections with

each other.

He invited ‘an old girl-friend in Vienna’ to join him in Arosa while his

wife remained at home in Zu¨ rich. This former girl-friend might just possibly

have been his first love Felicie, who had an infant daughter, although

her husband had now left her. Whoever it may have been, the effect on

Schro¨ dinger’s creative powers was dramatic, and he began a twelve-month

period of sustained creative activity;Weyl once said that Schro¨ dinger did his

great work during a late erotic outburst in his life, a striking example of the

association in some people between sexual activity and scientific discovery,

something Schro¨ dinger himself was quite open about.

When he was enthralled by an important problem, Schro¨ dinger was

able to achieve intense and absolute concentration, bringing to bear all his

great mathematical powers. Soon after his return to Zu¨ rich he had found

the relativistic wave equation to which his name is attached. When asked

whether he had enjoyed the skiing at Arosa, he said that he had been

300 From Ehrenfest to Schr ¨ odinger

distracted by a few calculations. If he had taken with him a copy of Methods

of Mathematical Physics by Courant and Hilbert, of which the first volume

had just been published, he might have found in it the kind of mathematics

he needed. Fortunately Weyl was at hand and could be consulted in person.

The original inspiration for the new theory came from the young

French physicist Louis de Broglie, whose profile occurs later. Schr ¨ odinger

published it, together with applications, in a famous series of papers in the

Annalen. When Planck received a copy of the first one, he wrote that he

had read it ‘like an eager child hearing the solution to a riddle that had

plagued him for a long time’; and after the second, ‘you can imagine with

what interest and enthusiasm I plunged into the study of this epoch-making

work’. He showed the papers to his colleague Einstein, who wrote ‘the idea

of your work springs from pure genius’.Arival theory had been developed by

Bohr’s disciple Heisenberg, and a protracted argument developed between

them; there was a good deal of controversy, but Schr ¨ odinger had earned the

professional and personal esteem of the mandarins of German physics. It

was at this point that he went to visit Bohr in Copenhagen. Although deeply

impressed by Bohr personally, he was not persuaded by his arguments, as we

have seen. Next Schro¨ dinger, who spoke English well, took up an invitation

to cross the Atlantic and give a course at the University of Wisconsin. He

went via New York and Chicago, both of which he disliked intensely, but he

liked Madison very much. The lectures he gave there were well received;

he turned down the offer of a permanent position on the faculty. Afterwards

he went on a tour that took him to Pasadena, where Millikan and Lorentz,

who happened to be visiting, sat in the front row of his lecture. On the

way back he stopped in Baltimore, where he was offered a position at Johns

Hopkins, but again he declined, because he had heard from Germany that

he might be invited to move to Berlin in succession to Planck, who was

retiring as head of physics at the Kaiser Wilhelm Institute. The testimonial

drawn up for this purpose provides a useful summary of his achievements

at that date:

For some years already he has been favourably known through his

versatile, vigorously powerful, and at the same time very profound

style in seeking new physical problems that interested him and

illuminating them through deep and original ideas, with the entire set

of techniques which mathematical and physical methods at present

provide. He has proved this method of working to be effective in the

treatment of problems in statistical mechanics, the analysis of optical

Erwin Schr ¨ odinger (1887–1961) 301

interference, and the physiological theory of colour vision. Recently

he has succeeded in an especially daring design through his ingenious

idea for the solution of the former particle mechanics by means of

wave mechanics in the differential equation he has set up for the wave

function . . . Schro¨ dinger himself has already been able to deduce many

consequences from this fortunate discovery, and the new ideas that he

has inspired with it in many fields are even more numerous . . . it may

be added that in lecturing as in discussions Schro¨ dinger has a superb

style, marked by simplicity and precision, the impressiveness of

which is further emphasized by the temperament of a South German.

Of the three being considered for the Berlin chair, Sommerfeld

was preferred to Schro¨ dinger, who in turn was preferred to Born. When

Sommerfeld declined to leave Munich, Schro¨ dinger was offered the post.

Every effort was made to persuade him to stay in Zu¨ rich. The physics students

organized a torchlight parade around the university to the courtyard of

his house, where they presented him with a petition. Schro¨ dinger was deeply

moved, but in the end it was a personal appeal from Planck that persuaded

him to accept the Berlin offer; as the result of doing so he automatically

became a German national.

Before beginning his duties in Berlin, Schro¨ dinger travelled to Brussels

for what proved a historic occasion, the most important of the Solvay

physics conferences. Although he had attended previously, this time he was

invited to give one of the prestigious lectures. The topic of the meeting

was electrons and photons. Schro¨ dinger’s lecture, on wave mechanics,

aroused considerable debate; Born and Heisenberg attacked it quite vehemently.

Schro¨ dinger was always something of an outsider, sustained by his

superior mathematical abilities and sceptical of any orthodoxy.

Among the science courses at the University of Berlin, Schro¨ dinger’s

was considered the best. He introduced an informal style of lecturing that

was new in a place where formality still prevailed. Many professors practically

read their lectures; he spoke without notes. Professors were expected

to dress formally; Schro¨ dinger usually wore a sweater and bow tie in winter,

an open short-sleeved shirt in summer. Later on he was often seen in

Tyrolean costume. For Schr ¨ odinger, as for other Berlin physicists, the weekly

colloquium was the great event, where new discoveries and theories were

discussed; Einstein played a leading role, as with careful questionings and

elucidations he sought to reach the heart of every problem presented.

Schro¨ dinger was elected to the Berlin Academy, at forty-two the youngest

302 From Ehrenfest to Schr ¨ odinger

member of the august society. Although his marriage was still floundering,

he had an active social life, including various affairs.

When the Schro¨ dingers moved to Berlin, the German economy was

recovering. The capital had the reputation of being the most licentious city

in Europe. Theatrical and musical life was flourishing, against an ominous

political background. As the economic recovery faltered, the Nazis saw their

chance and, after the 1933 elections, seized power and, as we know, instituted

the policies which deprived Jewish scientists of their positions. At

first Schro¨ dinger was one of those who thought that the ‘Nazi madness’

would be over in a couple of years, but soon he became convinced that they

would be in power for a long time. When Lindemann came to discuss the

situation, one of the people he saw was Schro¨ dinger and he was surprised

to find that, although not one of those personally affected, his disgust with

the Nazis was so great that he was prepared to leave Germany if Lindemann

could arrange something for him in Britain. Lindemann persuaded Magdalen

College, Oxford, to offer Schro¨ dinger a fellowship, to be supplemented by

a research appointment from industry, giving him an income comparable

to that of an Oxford professor. Schro¨ dinger took study-leave from his position

at Berlin, although he was not expected to return. He and Annemarie

deposited some of their possessions in Zu¨ rich for safety and then went on to

join Born andWeyl in the Italian Tyrol. For some timeWeyl had been having

an affair with Annemarie, while Schro¨ dinger himself had been having an

affair with Hildegunde March, the wife of one of his Berlin colleagues. Before

long he was treating her almost as his mistress; she had a child by him, a

daughter christened Ruth Georgie Erica.

En route to Oxford Schr ¨ odinger attended the seventh Solvay conference,

this time on nuclear structure and nuclear reactions. His formal

admission to Magdalen was accompanied by the news that he had just been

awarded the Nobel prize in physics, jointly with the Cambridge physicist

Paul Dirac, whose profile follows later. Although Lindemann and others did

all they could to meet Schro¨ dinger’s requirements, for example by providing

somewhere for the March family to live, Schro¨ dinger was dissatisfied with

his status in Oxford.

Across the Atlantic at Princeton there was a prestigious chair in mathematical

physics to be filled. Although the Princeton physicists were hoping

to appoint Heisenberg, they invited Schr ¨ odinger to come over on a visiting

lectureship. When he did so his lectures were, as usual, models of scientific

exposition, and he was offered the vacant professorship on the spot. After

he had returned to Oxford he declined the offer; it seems that he might have

Erwin Schr ¨ odinger (1887–1961) 303

accepted had it been an offer from the Institute for Advanced Study, where

he would have had Einstein and Weyl as colleagues.

Although the funds Lindemann had obtained from British industry

were almost exhausted by the end of 1935, Schro¨ dinger was given a

two-year extension of his grant. However, when he heard that a professorship

in physics was soon to become vacant at Graz, he went over to

Austria, where he was offered a full professorship at Graz combined with

an honorary professorship at Vienna. While awaiting official confirmation

of this, he received an offer of a chair at Edinburgh, but, owing to a bureaucratic

delay, the necessary permission for permanent British residence had

still not arrived when the formal offer came from Graz. So he went back

to his homeland and, as we have seen, it was Max Born who moved to

Edinburgh instead. Annemarie spent most of the time in Vienna with her

mother while Hildegunde and the child Ruth were living in part of their

house.

For the next few years Schr ¨ odinger’s research was inspired by the cosmological

theories of Arthur Eddington, who in his prime had virtually created

the discipline of stellar astrophysics, although later he became a lonely

and controversial figure who believed that scientific knowledge derived not

from the external world but from the abstract structure of human thought.

Schro¨ dinger loved the Tyrol, but was hoping that a vacancy in Vienna would

arise so that he could move to the Austrian capital. Unfortunately the political

situation in his homeland was deteriorating rapidly. In 1938, after the

crisis which led to the Anschluss, the Nazis straightaway extended to a compliant

Austria the anti-Semitic policies which were in force in Germany.

The new Nazi Rector of the university advised Schro¨ dinger to make a

‘repentant confession’, which was then published in the press, beginning

as follows: ‘in the midst of the exultant joy which is pervading our country,

there also stand today those who indeed partake fully of this joy but

not without deep shame because until the end they had not understood the

right course’, with much more in the same vein. In future years Schr ¨ odinger

would always regret this letter, which at first his friends thought could only

have been written under duress, until they found out that the Schro¨ dingers

were enjoying a peaceful skiing holiday in the Tyrol.

Although Schr ¨ odinger had nothing but contempt for the Nazis, he

never expressed any public criticism of the regime. By this time the German

physicists, notably Heisenberg, had adapted themselves to the absence of

their Jewish colleagues, and at the meeting in Berlin to celebrate the eightieth

birthday of Planck the Schro¨ dingers were warmly welcomed. However,

304 From Ehrenfest to Schr ¨ odinger

on his return to Austria he found a letter of dismissal from the honorary

position he held in Vienna. Despite the notorious letter quoted above, he

was regarded as anti-German and within a few months he received another

letter of immediate dismissal, this time from the University of Graz, for

‘political unreliability’. The manner in which he had left Berlin had not

been forgotten.

Realizing that there was no time to lose, the Schro¨ dingers took the

train to Rome with just a few suitcases, leaving almost everything else

behind. The Italian physicist Enrico Fermi met them at the station and

lent them some money. Like Fermi, Schro¨ dinger was one of the original

members of the Papal Academy of Sciences. In Rome he heard that Eamonn

de Valera, the prime minister of Eire, wanted to see him in Geneva, where

he was presiding over a meeting of the League of Nations. De Valera, who

had an interest in mathematics, explained that he was preparing legislation

for the Irish parliament to establish an Institute for Advanced Studies in

Dublin and that he wanted Schro¨ dinger to be a member of it. He warned

Schro¨ dinger that war was imminent and advised him to go to England or

Ireland as soon as possible.

Schro¨ dinger agreed to de Valera’s proposal, but did not proceed directly

to Dublin. Instead he spent some time at the University of Ghent writing

an important research paper, the first for some years, on the expanding universe.

But for the outbreak of war, the University of Ghent would have

conferred on him his first honorary degree. The Schro¨ dingers were joined

by Hildegunde and Ruth from Germany, and then they all travelled as far

as Oxford. Lindemann and others who had made such efforts to be helpful

before were not pleased to see them again. There was a problem obtaining

British transit visas, since they were now classed as enemy aliens, but

Lindemann did them one last favour by using his influence, and by October,

1939 they had reached Dublin.

The Schro¨ dinger me´nage, including Hildegunde and Ruth, settled

into a small house on the coast; they had come down in the world, but

Schro¨ dinger recognized that the new institute was being generously funded

by the taxpayers of a relatively poor country with many demands on its

resources. Schro¨ dinger adjusted surprisingly well to life in Dublin, in those

days by no means a prosperous city but one with a rich cultural life. Under

his leadership the institute became a lively centre for advanced study in

theoretical physics. There was a physics colloquium with forty-five participants,

including a number from Britain, notably Dirac and Eddington (both

monomaniacs, according to Schro¨ dinger). Like Einstein in Princeton, he

Erwin Schr ¨ odinger (1887–1961) 305

dedicated himself to the vain quest for a unified field theory encompassing

both electromagnetism and gravitation.

Rather than discuss his fruitless efforts in that direction, it is more

interesting to describe what he did in biology. This was not an entirely new

field to him; at a lecture in Berlin in 1933 he had discussed the question

of why living organisms contain so many atoms. He did not pursue the

question at the time, but now he returned to it and reached the conclusion

that the chromosome is a message written in code. The genetic code of

course is one of the fundamental principles of the new science of molecular

biology. A few earlier works had hinted at such an idea, but Schro¨ dinger was

the first to state the concept in clear physical terms.Abook he wrote entitled

What is Life?, which was published in 1944, had an enormous influence,

although it did not go down well in Catholic Ireland because it contained

a scornful debunking of western religious teaching. The book had a major

influence on the microbiologist Francis Crick.

Schr ¨ odinger was nearly sixty by the time the war ended, but he had

energy for two more love affairs. He was convinced from previous experience

that scientific activity would be promoted and sustained by erotic excitement.

The first was with the Irish actress and political activist Sheila May

Green; her own marriage was childless, but she had a child by Schr ¨ odinger

who was brought up by her husband after she had left him. Sheila was followed

by yet another conquest; this again produced a daughter. Meanwhile

Schro¨ dinger began to attack the quest for a unified field theory with fresh

enthusiasm. He announced a great breakthrough at the institute, which was

trumpeted by the press, but Einstein was soon able to convince Schro¨ dinger

that he was mistaken. After this embarrassing debacle he began to devote

more of his time to philosophy.

He and Annemarie now became Irish citizens, while retaining their

Austrian nationality. When he attended the first post-war Solvay conference,

he was left with the impression that no-one was much interested in

his current research. He was invited to give a course at Harvard, on his philosophical

ideas, but declined when he found out that he would have to stay

on afterwards to grade the papers of the students who took the course. He

wanted to return to Austria, especially to his beloved Tyrol, but the country

was under four-power occupation. He was afraid to enter the Russian

zone, but in 1951 spent a termat the University of Innsbru¨ ck, in the French

zone, where Hildegunde’s husband was on the faculty. At one point it

appeared that Schr ¨ odinger might remain there on a permanent basis, but

nothing came of it.

306 From Ehrenfest to Schr ¨ odinger

By 1955 the Russians had withdrawn and the way was clear for him to

return to Vienna. He arrived there to be treated as a celebrity, festooned with

honours. After he had given some lectures, he was appointed to a special professorship

at the University. His final academic year was 1957/8, although

he remained active as an emeritus professor. He was decorated with the

prestigious German order ‘Pour le M´ erite’ in 1957, as was Lise Meitner at

the same time, but he never went back to Germany. Already Schro¨ dinger’s

physical health, especially the condition of his heart and lungs, was causing

concern; he was close to the end of his life. He died peacefully on January 4,

1961, at the age of seventy-three, and was laid to rest at Alpbach in the

Tyrol, which he used to say was his favourite place on earth.