BRAGG CENTENARY

Introduction

The celebrated autobiography of Benvenuto Cellini begins with the words “it is the duty of all men who during their life-time have accomplished anything of merit to write an account of their life with their own hand”. In default of such a self-recorded history it may perhaps be said with equal justification that this obligation devolves upon the contemporaries or successors of a famous man to see that the story of his life and deeds is fully and faithfully recorded in order that posterity way know what manner of man he was to whom it owes a debt of service or achievement. This public duty is, in fact, one of those specifically laid down in the terms under which the John Murtagh Macrossan Foundation was established, and it has been previously honoured on many occasions in this series of lectures.

In selecting the “Life and Work of Sir William Bragg” as another to be commemorated under this Foundation, the Professorial Board of the University of Queensland has made no unworthy choice; in honouring me with an invitation to undertake the task, reason was doubtless found primarily in the fact of my succession to him in the Chair of Physics in the University of Adelaide.

The association thus entailed with his former colleagues on the staff of the University, his relatives and friends in Adelaide, and old students who attended his classes does indeed place me in a privileged position to obtain from them and from other sources, first-hand information concerning the man himself and the details of his life while he lived among them; further, it was, no doubt, assumed that a Professor of Physics might be expected to posses, at the least, a general acquaintance with those aspects of Physical Science, to which, in the main, Bragg’s researches and discoveries belong.

I can only hope that such advantages ass I may possess in these respects may serve in some degree to outweigh the disadvantage of my inexperience in the art of literary presentation in this field.

But whether or not the choice of a biographer has been wisely made, it was at any rate a wise decision not to postpone too long the interval between the death of the subject of the biography and the collection and recording of the factual data which must form the foundation for a story of his life.

The apocryphal elements in the life-histories of many famous men warn us how soon in the absence of reliable temporary records, many things we would wish to know concerning their lives are either irrecoverably lost, incrusted with the lore of legendary fiction or shrouded in the mists of myth. How soon too, does the opportunity pass for the biographer to secure from the relatives, friends and acquaintances of one deceased, direct testimony concerning his personal characteristics, the circumstances of his daily life and all the trivial yet nevertheless significant actions and events without knowledge of which he can at best prepare a mere factual record devoid of the human appeal and living semblance of a “flesh-and-blood” portraiture.

Already, in the case of Sir William Bragg, two only of his former colleagues on the staff of the University of Adelaide — Sir William, Mitchell and Sir Douglas Mawson survive, and only two relatives by marriage — Miss L.G. Todd and Mrs. Guy Fisher are now resident in Adelaide.

Sources of Information

His only, surviving son, William Lawrence (now Sir Lawrence) and his only daughter Gwendolen (Mrs. Alban Caroe) are resident in England. Sir Lawrence Bragg has been so kind as to send to me excerpts from an autobiographical statement of his father concerning his early life prior to coming to Australia.

Miss Lorna Todd has furnished me with a most interesting statement setting forth her reminiscences of Bragg’s associations with her father, Sir Charles Todd and his family culminating in his marriage to her younger sister. Sir William Mitchell also has told me much concerning his colleague during his tenure of the Chair of Mathematics and Physics in Adelaide University. Sir John Madsen, who was Lecturer of Electrical Engineering in Adelaide during the last years of Bragg’s term as Professor of Physics and who co-operated with him in research work, still recalls clearly the conversation in which Bragg told him of the new point of view at which he had arrived regarding the nature of alpha-rays, a point of view which subsequently led to a triumphal march of successes in experimental research. Others, whose acquaintance with him was of a more limited character such as that of student to teacher — have contributed items of personal recollection.

My own opportunities of a close personal acquaintance with Bragg were unfortunately few, comprising only one brief meeting in Melbourne shortly prior to his departure to England; subsequently, occasional meetings and conversations during my visits to England in 1919, 1927 and 1931, and occasional correspondence.

Of literary sources available to me the most valuable as a record of his work and picture of his personality is the excellent obituary written by Professor Andrade of London University for the Royal Society of London.

A full appreciation of his scientific achievements could, of course, only be based upon a critical study and evaluation of — the numerous papers contributed by him to the proceedings of scientific journals, or as set forth in the several books in which the contents of these were collected and integrated. It is neither my intention nor my prerogative to attempt more in these lectures towards such an appreciation than to endeavour to indicate the salient points in method and the main results of his researches. Sir Lawrence Bragg has informed me that it is his intention to write a full biography of his father and an account of his scientific work when in a few years time his retirement from office will afford him the leisure to undertake the task.

In the realm of popular exposition Bragg was an acknowledged master. Several lecture-courses which he gave at the Royal Institution are published in book form. These also aid his biographer in his efforts to attain the difficult goal of “presenting a life-work in full and significant delineation”.

Heredity

William Henry Bragg was the son of Robert Henry Bragg who, at the early age of 25, gave up a post in the British Merchant Navy to purchase and cultivate a farm in the village of Westward near the town of Wigton in Cumberland. His mother, Mary Wood, was the daughter of the Vicar of the parish.

There seems to be little evidence to permit of a decision on the controversial and invidious question as to whether the son owed his outstanding intelligence to his father or to his mother. Moreover, in the light of the science genetics, the question is over-simplified, the grand-parents and even remoter progenitors are claimants also to whatever congenital merit or demerit is assigned to any one of their descendants.

Heredity, despite the mathematical regularities which the work of Mendel and his successors have revealed in its operation, can play strange tricks. The appearance in their off-spring of characteristics which neither parent is eager to claim as his (or her) donation — I have been told — a not infrequent source of marital altercation; the occasional Emergence of individuals of exceptional ability from a line of undistinguished ancestry (such illustrious names as those of Newton, Faraday and Einstein immediately occur to a physicist) may seem even more inexplicable.

On the other hand there is abundant evidence to show that, in common with other physical and mental characteristics, exceptional ability can and does descend from generation to generation. In England we have as illustrious instances of hereditary scientific genius the families of Darwin, of Herschel and of Huxley. There is already sufficient evidence to justify the addition of the name of Bragg in his honourable gallery.

The possession of exceptional scientific and mathematical ability is fully attested for two generations in the achievements of father (W.H.) and son (W.L.); less well known is the possession of distinctive artistic talent by the father (W.H.), his second son Robert (killed at Gallipoli) and his daughter Gwendolen (now Mrs. Alban Caroe). I learn from Miss Todd that the genes of genius have persisted into a third generation. Sir Lawrence Bragg’s eldest son has had a distinguished scholastic career in mathematics at Rugby and at Cambridge, where, in succession which is probably unique, he is a Scholar of Trinity. In the second son the gene of artistic ability is again strongly dominant.

Childhood and Early Education

Both Bragg’s parents died young — his mother when he was only seven — and the responsibility of providing him with a home and education was willingly accepted by an uncle, William Bragg, who lived in the town of Market Harborough in Leicestershire, and had played a part in the re-establishment of the local grammar school.

In some notes written by himself at the age of 70 concerning his early life, which I owe to the courtesy of Sir Lawrence, Bragg has given an interesting account of his experience at this school. It was not a very large one. “I was one of the six boys”, he said “with which it opened. At the end of the first year I was given a scholarship exempting me from payment of fees. At the prize-giving — there were many more than six boys at that time — my name was called out and I went up to the desk to get the scholarship, not knowing what it was. I was puzzled and disappointed to go back empty-handed.”

The precocity which is a common if not an invariable indication of future genius, was not lacking in the school-boy Bragg. At the early age of eleven he entered for and passed in the “Oxford Junior Locals”, the youngest boy in England to get through.

His home life during this period, despite the care and affection bestowed upon him, was perhaps unfortunate in respect of the narrow religious atmosphere which prevailed, with its insistence on an unquestioning acceptance of prevalent orthodox beliefs.

At the age of 13, having probably reached the limit of the school’s capacity to go further, his uncle sent him to King William’s College in the Isle of Man. Here he rapidly developed a proficiency in his studies - and especially in mathematics — on the one hand and in school sports on the other.

This latter accomplishment was fortunate, for he confesses to having been a shy and retiring boy — though it seems likely that this may have been due mainly to the fact that he was younger than his classmates — and to excel in games was probably then, as now, a school boy’s surest passport to popularity with his fellows. He rose, at any rate, to be Head of the school. In 1880 he entered for the examination for Scholarships at Trinity College, Cambridge, and was awarded one, but on advice of the authorities, delayed his entrance for a year.

It was in this year, at the age of 18 — a critical period in the emotional life of an adolescent — that the school he attended was, in Andrade’s words, “swept by a storm of religious emotionalism” in which Bragg by reason of the revolt of his reason and sympathy against the irrational and inhuman dogmas of Athanasian theology, was involved so deeply as to recede rather than to progress in his studies and failed at the next scholarship examination to equal his previous performance. Nevertheless, he was awarded a minor scholarship and entered Trinity College, Cambridge University in 1881

In this new environment where — unless the social and intellectual climate of Cambridge was very different then from what it is today — at atmosphere of spiritual freedom and intellectual tolerance envelops the formalities of religious observance and the dogmas of theology this brief unhappy interlude of religious melancholia could not endure, and the young Bragg entered upon a new life full of interest and enjoyment.

He now lived and worked as a student in Trinity College he has told in his own words, written in 1927.

“I went up to Cambridge in 1881, taking the rather unusual course of beginning work there in the Long: I suppose I was in Cambridge six weeks or so, July and part of August. But I forget the exact date. I had rooms in master’s Court. I appreciated thoroughly the beauty of the whole place; and I liked going to Routh’s classes. It was lonely, because I was doing the unusual thing: and I had no companions. But it was good all the same. As a scholar of the College I went up every Long afterwards: it was always a jolly time. Very few restrictions: just the regular classes three times a week with Routh, and the preparation for them. After that tennis in plenty: boating on the river above Cambridge, and the summer weather, and Cambridge looking its best. I tried during that preliminary long to get through an exam that would excuse me the Littlego: and I failed in Latin, which seems to me now to be very odd, as I had studied Latin from the time I was seven and given a lot of schooling time to it, and worked conscientiously too! I had to take the Littlego, in November after all.

Cambridge gave me a good time, of course: although I might have done mach better if I had known more or been more easily sociable. I ought to have gone to lectures on other subjects than mathematics, and taken an interest in other things. It simply did not occur to me. I could not afford, or thought I could not afford, to join the Union or the Boating Club: which cut of f a good many opportunities. I had none of those experiences of discussion of the world and its problems with other young men, which many men seem to look back upon with so much pleasure. I worked at the mathematics all the morning, from about 5-7 in the afternoon and an hour or so every evening, and then bed fairly early. Every afternoon I played a game, generally tennis, or went for a walk: my tennis was fairly good, so that I always found people ready to play.”

There is an omission of a sentence or two in this except which can be made good from Andrade’s obituary; it refers to the congratulations received from friends on his success in the Tripos examination. One of these was A.N. Whitehead, later of world-wide reputation as a mathematician (he offered a derivation of the principle of relativity alternative to Einstein’s) and philosopher (he is now Professor of Philosophy at Harvard) “who came and shook me by the hand saying ‘may a fourth wrangler congratulate a third.’” He had been fourth the year before.

After his crowning success, Bragg continued his mathematical studies and sat for the more advanced examination, Part III of the Tripos, as it then was. of the result of this he says, humorously, “I believe that none of us did too well, but nearly all got Firsts because the Senior Wrangler did not do any better than we did and they could not give him a second.”

Appointment to the Adelaide Chair

Bragg, in his reminiscences, tells the story of how he came to apply for and be appointed to a Professorship in the University of Adelaide. In 1885 the Chair of Mathematics and Physics had been rendered vacant by the resignation of Professor Horace Lamb, who was the first occupant at the date when the University was established in 1874 and who now wished to return to England, where he had been offered the Chair of Pure Mathematics in the Owens College, Manchester. According to a practice still customary, the vacancy was advertised in the English press. Bragg had seen the advertisement but had not though of applying, believing that his youth (he was only 23) and entire lack of teaching experience would make his chance of appointment negligible. However, on his way to a lecture by J.J. Thomas (afterwards famous for his discoveries in the realm of atomic physics) he was joined by the lecturer, with whom he also had social acquaintance. The conversation turn on the Adelaide Chair. As a result of Thomson’s advice Bragg telegraphed an application — it was the last day of entry.

There were only a few applicants and Bragg was one of the three on the “short list” selected for interview. The interviewers were Professor Lamb, J.J. Thomson, and the Agent-General for South Australia, Sir Arthur Blyth. They also called in, to assist them in making a final choice, an Adelaide man who happened to be in London at the time. He was Mr. (afterwards Sir) Charles Todd who certainly did not know then that he was helping to bring to Australia not merely a professor but his own future son-in-law.

Another applicant much senior to Bragg was a Senior Wrangler of great ability whose claim to preference was, however, discounted by, his partiality for the contents of the bottle which, if it sometimes cheers, too often inebriates. So the choice fell upon Bragg, to whom it was first conveyed by a telegram from Australia that same evening, worded “As new professor of Mathematics and Physics in Adelaide University would you give some particulars of your career.” Bragg’s delight in an appointment which offered him, in his own words, “an assured position, a salary beyond all expectation (£800 a year), a new country with all the adventure of going abroad to it, and a breakaway from being a subject, to be now my own master” was tempered by the distress which the prospect of losing him caused to his worthy and benevolent old uncle to whom he was evidently as dear as a son, a distress, however, relieved by pride in “his nephew the professor”.

Fifty years later Bragg could still recall and record the enthusiasm and excitement of the preparations for departure: the novel experiences of the voyage to Australia in the largest vessel of the P. & 0. fleet — the “Rome” of 4,500 tons — and his efforts to learn something about physics (for his studies at Cambridge had been confined to Mathematics alone) during the voyage by reading Deschanel’s Electricity and Magnetism!

Long years afterwards, when I paid him a visit in London and congratulated him on his appointment as Fullerian Professor of Chemistry in the Royal Institution, he said with humorous enjoyment: “The joke of it is that I always seem to be appointed as professor in subjects about which I know nothing.” It was true, no doubt, that when he went to Adelaide he knew little or nothing of the formal physics of the text book; possibly true that when he took the Fullerian Chair of Chemistry not much more of text-book Chemistry. But these deficiencies of academic knowledge had the advantage of leaving him with a clean sheet on which to write his own self-acquired knowledge on these subjects and, as one of his most distinguished disciples (Dr. W.T. Astbury) says: “He had the most amazing faculty of taking up a subject on which he had only the foggiest ideas to begin with and quickly improving it out of all recognition.”

From the first day of his arrival Bragg thoroughly enjoyed his life in Australia. He was fortunate in that the acquaintance already made in London with Charles Todd — who was Director of the Adelaide Observatory — immediately opened to him the door of a delightful domestic circle comprising in addition to the father and mother, three daughters and two sons. Very soon he, with a new friend, the late Dr. Alfred Lendon, became a regular Sunday afternoon and evening visitor at the Observatory home. “We were a cheerful party there,” writes Miss Lorna Todd (who was eight years old at the time). “Fierce arguments over religious and social subjects were the order of the day amongst the men. The irresponsible and illogical chatter of my sisters” (thus irreverently did this child of eight characterise the conversation of her older sisters) “delighted him most. It was a revelation to a young man who had been taught to weigh every word he uttered, and he blossomed under the cheerful and inconsequent atmosphere.”

A very natural and happy sequel to this idyll of domesticity was the marriage in the year 1889 of William Henry Bragg to Gwendoline, third daughter of Sir Charles and Lady Todd.

Of this marriage there was issue to sons, the first, William Lawrence (now Sir Lawrence, Director of the Cavendish Laboratory); the second, Robert, who was killed in the Gallipoli misadventure of World War I, and one daughter Gwendolen (Gwendy) now Mrs. Alban Caroe of London.

Bragg, from the very first, was marked as a born teacher and lecturer. Professor Andrade says (quoting — no doubt from hearsay — some Adelaide source) that in his early days “he was one of the least impressive of lecturers.” If there is any justification for all this disparagement it may rest either on his complete inexperience in the art of lecturing or in his disdain of the use of rhetoric in which one of his colleagues, himself a master of that “poison of sincerity” was wont to appraise the quality of another’s oratory.

Students who, at a later date, attended his lectures have one and all agreed in crediting him with exceptional powers of lucid exposition, so much so, indeed, that they accuse him of having been able to invest his discourse on abstruse topics with an altogether delusive simplicity. His interest and influence in educational matters soon spread beyond the precincts of the University. The curriculum of the secondary schools in South Australia, as more or less in all Australian States, dominated then as it is now by the public examinations syllabus, and, in particular, by the subjects demanded for matriculation, was still modeled on that of English public schools with their almost exclusive emphasis on the ancient languages and mathematics. Any scientific subject, if grudgingly permitted an hour or two a week of the time­table, was taught largely as an exercise in memorisation of the text-book with little or no appeal to observation, lecture-demonstration or laboratory exercises by the student.

Bragg was not long in raising his voice in criticism of this defect and in pleading the claim of science to be regarded as an educational medium of high practical value.

At the commemoration address which he gave in December, 1889, he concedes, doubtfully, the claim that the classical system of education “may perhaps develop in the younger generation the capability of fulfilling duties in certain traditional ways,” but, he continues, “it does not so train their minds that, having a knowledge of the tools that modern science provides and judgement as to what may be done with them they may strike out for themselves new kinds of Work and new methods of working.”

In the same address and on subsequent occasions he strongly advocated the introduction of practical work in school physics. “Every year,” he said, “I have answers from book-taught candidates which show a practical ignorance of physics.” To emphasise his views he relates an amusing story of a youth’s answer to an oral examination to the question:

“What is the use of a compass?”

After much hesitation came the answer:

“To find the latitude and longitude.”

On the examiner asking “Could you do it?” the examinee promptly replied: No, Sir, but YOU could.”

So far as the schools went, his exhortation, if heeded at all, led only to the casual and perfunctory performance of an extremely elementary type of practical exercises in physics in one or two of the larger schools. But, in his own University classes, systematic practical courses were very soon established, he himself for many years acting as instructor with little or no junior assistance.

His scientific interest seems to have turned, immediately after the assumption of his duties, from mathematics to physics. Indeed the mathematics required for the Cambridge University examinations in those days was perhaps not of a type to inspire many to pursue it further. From the first he found particular pleasure in demonstrating, both to his students in the routine lecture-courses, and in public lectures and conversaziones, the more novel and spectacular miracle of scientific discovery. In these latter his young wife’s social talents proved an invaluable asset.

Success in presenting the results of scientific research to a popular audience, unacquainted for the most part with the basic facts and principles of the special science in question, demands from the lecturer not merely a thorough understanding of his subject but the ability to translate the technical terminology of science into the language of every-day usage. In this art, Bragg was singularly gifted. In the light of the nature of his subsequent achievements it is interesting to note that in 1895 the subject of a course of extension lectures was “Radiation”; in 1896 “X-rays”; in 1897 “Sound”. Undoubtedly the task of preparing these lectures and the experience gained in the technique of experimental demonstration must have served to lay a solid foundation of knowledge and skill which stood him in good stead in his future researches in the fields of radio-activity and X-rays.

Bragg also followed with keen interest the news which reached Australia from time to time of the remarkable discoveries and developments which were at this time (1895 and onwards) taking place in Europe in these last-named subjects and in wireless telegraphy.

But he did more than merely read about them and talk about them. He promptly set about reproducing them by his own efforts with the very slight amount of technical assistance and meagre stock of instruments and apparatus which his laboratory possessed. Especially was his interest aroused by the discovery of X-rays by Professor Rontgen of the University of Wurzburg in 1895. Rontgen published his discovery in December, 1895; news of it reached Australia in a brief cable in January, 1896.

In common with Professors of Physics in other Australian Universities, Bragg was immediately stirred to find means to produce this new kind of “invisible light”.

X-rays are produced by the impact of an electron stream on any solid object and to realise this all that is essential is an evacuated glass bulb into which are hermetically sealed two metallic electrode, and a source of high tension electricity. The type of vacuum-tube used by Rontgen when he made his immortal discovery, was first designed and constructed by Sir Wm. Crookes and employed by him in his researches on the passage of electricity through rarefied air; the high-tension electricity was supplied by a Ruhmkorff induction-coil. The meagre equipment of the physics laboratory in those days did not include a Crookes tube and to have imported one would have meant a delay of several months. Fortunately Bragg’s laboratory assistant, Mr. A.L. Rogers, was skilled in the art of glass-working and by Bragg’s direction at once proceeded with the attempt to construct a small tube. In this he was ultimately successful, but before the first tube was satisfactorily completed a citizen of Adelaide, Mr. S. Barbour, returned from a visit to England bringing with him two Crookes tubes purchased from a British firm. With the co-operation of Professor Bragg remarkably good radiographs were taken with these tubes.

Subsequently Mr. Rogers made and evacuated many tubes which were successfully employed in medical radiography.

Professor Bragg’s eldest son, William Lawrence (now Sir Lawrence) was a child of five at the time of these experiments in which, nevertheless, he was on one occasion a participant. In his foreword to the publication of Messrs. Watson and Sons’ book entitled “Salute to the X-ray pioneers of Australia”, Sir Lawrence writes: “I well remember my father’s first experiments with X-ray tubes, although I was only six years old at the time. I think I must have been amongst the first to be employed as a patient. I had smashed my elbow badly by a fall and was taken to a cellar in the University for the exposure. The flickering greenish light, crackling and smell of ozone were sufficiently terrifying to impress the incident deeply in a child’s mind. When I think, however, of the early experiments, the interest which they aroused in medical men in Australia is not their chief significance to me! I see them as fore-runners of my father’s interest in the ionisation of gases leading to his experiments with X-rays from radium and finally the experiments on the diffraction of X-rays by matter which we carried out together.”

The letter “X” which Rontgen chose to designate this new type of radiation, had reference of course to his confessed ignorance of their true nature. (His tentative hypothesis: “Ought not the new rays to be ascribed to longitudinal vibrations in the ether?” was fallacious.) It was not until 1912 that the experiments of von Laue in Germany, confirmed and extended in the next year by the Braggs, father and son, definitely proved them to be essentially identical in character with ordinary light. But among the apparatus which Bragg left behind him in the Physics laboratory was a large prism made of pure sulphur. On the testimony of Sir Lawrence Bragg, quoted in the publication just referred to, this was made with the special object of testing whether a beam of X-rays would be refracted in passing through this prism. If this recollection is correct it shows that the problem of elucidating the nature of X-rays was already occupying the elder Bragg’s attention many years before its final solution. (I am personally somewhat doubtful of the correctness of this opinion, recalling the answer given to my question by Professor R.W. Chapman who as a lecturer under Bragg was in a position to have first-hand knowledge that the prism was used for experiments on the refraction of electric (Hertzian) waves.)

In the same year in which Rontgen discovered X-rays a young Italian, Guglielmo Marconi, was experimenting in his home town of Bologna on the transmission of signals by means of wireless telegraphy. Coming to England (his mother was Irish) in 1896 he found encouragement, financial support and technical assistance from the British General Post Office, and we all know of the remarkable developments in wireless communication which followed. In 1898 Professor Bragg was granted a year’s leave of absence to visit England with a commission to inquire into matters of educational interest. His contacts with many eminent men of science must have created an interest in this new method of communication, for soon after his return he began experimenting in wireless transmission, first within the University and then from a transmitting station in the Observatory grounds to Henley Beach — a distance of about five miles. I quote from Miss Lorna Todd’s lively account of this event: “I think I am right,” she says, “in saying that the first wireless pole to be erected in Australia was in the Observatory grounds. A receiving pole was put up on the sand-hills at Henley Beach. My brother-in-law did much experimental work there. One afternoon I remember that my father asked me to pack tea and drive down with him to Henley Beach, saying he would send a ‘wireless’ to say that we were coming. I felt a very ‘doubting Thomas’ as I packed a specially nice tea and tied paper around the blackened picnic billy-can (there were no thermos flasks in those days). However, when we got within sight of the tall pole on the sand-hill there was my brother-in-law waving his arms and his cap, as thrilled as any schoolboy that the message had come through. It seemed a miracle. Both he and my father were almost boyish in the delight and the fun of the discoveries then being made so rapidly in science.”

First Original Research Work in Adelaide

It has been a matter of remark by some who have discussed or commented upon Bragg’s scientific career that his entry into the arena of scientific research should have been so long delayed.

It was not, in fact, until he had attained the age of 46 and had occupied the Chair of mathematics and Physics in the University for 18 years that he published anything of a quality entitling it to be considered as an important contribution to existing knowledge.

This long interval during which his genius for experimental research lay latent, is indeed an exception, though by no means a solitary one, to the general rule that creative imagination and scientific activity are at their highest in the spring-time or early summer of life.

In Bragg’s case there are plausible grounds of explanation for a seasonal retardation.

As already stated, his natural interests were those of the physicist, rather than of the “pure” mathematician, yet his whole academic experience previous to his election to the Adelaide Chair had lain exclusively in the former discipline. Thus before he could even glimpse the horizon which bounded the great sea of existing physical science at that date — a horizon more-over which was expanding so rapidly that it continually receded from the voyager pursuing it - he had an immense leeway to make up.

It is, of course in that unknown land beyond the horizon that lies the realm of scientific discovery, the realm of “research”.

But that word had ‘not, half a century or earlier ago, even in scientific circles -and certainly not in the politics of University finance — attained the portentous significance which to-day entitled it to vie in blessedness with “Mesopotamia” of sacred utterance.

Research had not yet acquired the status of a professional business. Rather was it then regarded as a natural and unforced by-product of academic employment and intellectual interest; subordinate, nevertheless, to the performance of the professor’s contractual obligation to train his students in the discipline of his special science, and to serve the general public as an authority and consultant on whom reliance could be placed for trustworthy information or wise counsel in all matters relating to his particular province of expert knowledge. It was in such a light, doubtless, that Bragg would view the responsibilities of his post.

His teaching duties at the outset were not onerous — there were in his first year only two students in the laboratory — but he did not hesitate to enlarge them whenever he saw occasion and opportunity.

For the benefit of those who could not attend during the day — mainly teachers in secondary schools — he instituted night-lectures and practical work, which he conducted.

Sir William Mitchell has told me of the surprise and pleasure which he felt when, on his arrival to occupy the chair of English in 1894, he found that a branch of the British Teachers’ Guild in which he had been interested in Scotland had already been established by Bragg in Adelaide. The high esteem in which he was held by the teaching profession and the gratitude and affection which they felt towards him were publicly expressed in tributes paid to him at a Teachers’ Conference held in July, 1908, shortly after his decision to accept the invitation from Leeds University had been announced.

It need not be denied that other and distracting human influences competed strongly with the “divine curiosity” which is the stimulus to the task of intellectual pursuits. Bragg was no indoor recluse; he was athletic in body as he was active in mind. He had a love for all healthy outdoor sports and pastimes and indulged his liking in actual participation. By his own account (already quoted) he played tennis well and no doubt, found in it pleasant opportunities of social recreation.

He took up golf and became one of several devotees among his colleagues (Mitchell and Henderson were fellow-practitioners of that Royal and Ancient game) and become so proficient that in the year 1907 he was beaten in the championship contest only on the last two holes of the course by Henderson. He introduced the Canadian game of lacrosse to South Australia and was for several years captain of the North Adelaide Lacrosse team.

To these athletic proclivites he added artistic talents of no man order. He sketched and painted in water colours with the hand and eye of a true artist. His wife shared with him this delightful talent — her teacher, Mr. H.P. Gill, would speak of her as a “first-class artist ruined by marriage”. During holidays husband and wife would sometimes sketch or paint, in company, a scene that took their fancy.

Gifted with a good musical ear, he not only enjoyed music but was himself a competent performer on the flute, an accomplishment which, on the testimony of Professor Andrade, he still practiced in his later London years.

Possessor of a fine presence and of all the social graces, he was a popular guest at social functions and entertainments whether public or private.

Fortunate in a happy marriage, blessed with and devoted to a family of two sons and a daughter, it might well be thought that he would have found his life in Adelaide so full and satisfying as to exclude all thought or wish of change or adventure either in the world of reality or the world of ideas.

But underneath all the pleasant preoccupation and lighter interests of his life there smoldered the urge to creative intellectual effort, nourished by the news of one great discovery after another in physics, and awaiting only the moment of inspiration to break out in action. Neither was this period of latent activity wholly devoid of all contribution to science.

In 1891 he contributed a paper to the Proceedings of the A. & N.Z.A.A.S. entitled “The elastic medium method of treating electrostatic theorems” and, as a sequel to this, in the following year another on “The energy of the electrostatic field”, published in the Transactions of the Royal Society of South Australia. This latter he amplified and presented again at the Brisbane meting of the Association in 1895.

These papers are all in the true Faraday-Maxwell tradition, in which the mathematical theory of electric and magnetic fields is based on analogy with the state of an elastic medium under stress.

They were essays in mathematical physics which put known results in a new light, ingenious variations on well-established theory, but they contained no result of importance previously unknown, and they neither reported nor suggested new lines of experimental research.

The occasion initiatory to such suggestion came with the duty of preparing the presidential address to Section A of the A. & N.Z.A.A.S. at the Dunedin meeting of the Association in 1904.

It is a recognised duty of sectional presidents to present to their section a resume of important recent advances in some branch of their special science. This was a time when new and surprising discoveries were revolutionising basic ideas in regard to the nature of matter, of electricity and of radiation and the mutual relations of these entities to one another.

Rontgen in 1895 had discovered X-rays; J.J. Thomson, in 1897, had experimentally proved the existence of a universal type of electrical sub-atom or corpuscle (now called the electron); Max Planck of Berlin had shown that light is radiated from atoms only in wave-pulses carrying energy quanta proportionate in amount to the frequency of the waves. Einstein, in the same year in which he published his epoch-making paper proving the relative character of space-extension and of time-duration had also suggested an atomic aspect in the nature of light as a explanation of its power to eject electrons from surfaces on which it fell. Niels Bohr of Copenhagen had successfully applied Planck’s quantum theory to solve the riddle of atomic spectra; the Curies, man and wife, following upon Henri Becquerel’s discovery of the radio-activity of the metal uranium, had isolated a new element, radium, a million times more active. Rutherford had analysed the radiation from radium and its products of disintegration and shown that it contained three entirely distinct kinds of rays — which he called the alpha (a), beta (a) and gamma (y) rays.

Into this last, as yet only partially explored territory of the science of radioactivity now entered Bragg. It came about in this way.

He chose as the topic of his presidential address, “Some recent advances in the theory of ionisation”.

Ionisation is a phenomenon which, as he states, “furnishes one of the principal methods by which the strange new properties of radioactive substances are made manifest and studied”.

Neither air nor any other gas in its normal condition conducts the electric current. But, when irradiated by a beam of ultra-violet light, or of X-rays, or of any of the three kinds of radiation emitted by radioactive substances, or when traversed by fast-moving electrons, a small fraction of the molecules of a gas normally uncharged or neutral may acquire either a positive or a negative charge by losing or gaining one or more electrons. These electrically charged molecules are termed “ions”, the gas is said to be “ionised” or in a state of “ionisation”, and if a voltage difference is applied between two rods or plates of metal immersed in the gas, the ions drift under the influence of the electric force towards one or the other, thus effecting the transfer of electricity which constitutes an electric current.

Already in 1904 a vast amount of experimental work had been carried out by scientists in investigating the nature and properties of ions, the laws of the ionisation-current and the properties of the various kinds of ionising agencies, in particular, the so-called alpha, beta and gamma rays of radium. and other radioactive substances

Bragg made a critical examination of the information thus available on the penetrating and ionising powers of these three kinds of radiation (alternatively, of the absorption which they undergo in passing through matter) . He came to the conclusion that there was a radical difference in these respects between the alpha rays and the other two, concluding that whereas the main reason for the reduction in intensity and ultimate extinction of a beam of beta-rays in passing through matter lay in the scattering of its moving electrons due to the repulsive forces exerted upon them by the fixed electrons of the atoms through which they passed, the alpha rays, by reason of their being nearly 2000 times as massive as an electron, suffered little or no such deviation from this cause and thus pursued a straight path until their initial velocity and energy were exhausted by the work done in ionising — or at least “exciting” — atoms through which they passed.

If this conclusion proved to be correct, it indicated, said Bragg, the following practical applications:-

(1) A means of identifying any species of radioactive element — provided it was an alpha-ray emitter — by observation of the range of its rays in air;

(2) a method of ascertaining what and how many different alpha-ray emitters were contained in a sample of any radioactive material;

(3) a method of comparing atoms of different kinds in regard to their “stopping power” for alpha-rays.

His conclusion as to a limited but definite range for alpha-rays was supported by an experiment described by Madame Curie.

A think film of the radioactive element polonium was placed on a metal plate. Parallel to this and at an adjustable distance were fixed two other plates an inch or two apart, the space between serving as an ionisation-chamber. The plate nearest to the radioactive source had a hole in it through which rays could pass.

It was found that ionisation resulting from entry of rays through this hole took place only when the distance from hole to polonium film was less than 4cm., indicating that the alpha-rays from polonium had a maximum range in air of that order.

On his return to Adelaide, Bragg promptly made preparation for an experimental attack on this problem. With the aid of a grant of X500 from a generous friend of the University he was able to purchase a small quantity of radium bromide and the necessary instrumental equipment. The Ionisation-chamber he himself designed and had constructed in his small workshop by a highly skilled mechanic, Mr. A.L. Rogers. In principle it was similar to that employed by Marie Curie, but it incorporated two vital improvements. In the first place, the actual ionisation-chamber was made very shallow, and the plate with the hole in it was replaced by a sheet of thin metal gauze which afforded easy access of the rays to the chamber. This enabled the effect of the rays to be measured at successively varying distances from their source. Secondly, by mans of stops placed vertically above the radium--covered plate it was ensured that only the rays which travelled perpendicular to the plate could reach the ionization-chamber, so that the same number of rays, if any, entered the chamber whatever its distance from the source.

Just as important as the provision of the instrumental equipment was the fortuitous and fortunate discovery and employment as an assistant of a young countryman named Kleeman.

This young man while employed as a blacksmith in the country town of Tanunda, had brought himself under Bragg’s favourable notice by soliciting his help in the solution of some mathematical problems. Correspondence resulted in an offer to Mr. Kleeman to come to Adelaide and, while pursuing his studies, to pay his way by acting as an observer in the experimental work on alpha-rays.

He turned out to be well-suited for this tedious employment; precise, careful and tireless in taking, day after day, the many hundreds of readings of the electrometer required to determine the “ionisation-curves” which showed the relation between the distance of the shallow-chamber from the source and origin of the rays, and the ionisation within it which measured their effects.

The results of these experiments vindicated Bragg’s expectation to the full.

As the distance of the chamber from the radium or other radioactive source was increased — starting from a distance of about I inch — the ionisation increased with it up to a very definite limit, after which it abruptly diminished to a zero value. If the source of the rays was radium without admixture of any of the other radioactive products of its disintegration, the maximum distance or range of the rays was 3 1/2 cm. If, however, these products, namely radon (formerly termed “radium emanation”), radium A, radium B and radium C were present, the complete ionisation curve showed unmistakably the emission of alpha-rays from four of these and indicated ranges of 4.1 for radon, 4.7 for radium A and 7.0 for radium CF (radium B emits beta-rays only).

These results not only demonstrated the correctness of Bragg’s views; they furnished at the same time a convincing confirmation of the disintegration theory of radioactive transformations which had been put forward by Rutherford and Soddy only four years earlier, during their brilliant partnership in radioactive research at McGill University. Realising this, Bragg immediately sent a letter to Rutherford — who was still at Montreal — informing him of the results of his experiments, and, as he subsequently avowed, “eagerly awaited his reply.”

When it came, warmly praising this new method of attacking the many still unsolved problems of radioactive phenomena, Bragg doubtless felt assured that any doubts he might have had as to the importance of his discoveries, could be cast aside and, with such assurance, from that time went confidently forward not only to extend his researches on alpha-rays but to embark on a fresh voyage in another sea as yet imperfectly explored: the nature of X-rays.

Parenthetically, it may be stated here that this first correspondence with Rutherford was not his earliest contact.

When Rutherford, at the age of 19, having been awarded that 1851 Exhibition, was on his way from New Zealand to England — where he was to become a research student in the Cavendish Laboratory (then under the direction of Sir J.J. Thomson) his ship called at Adelaide and he took the opportunity to pay a hurried visit to the University and call upon the Professor of Physics. He found him in a photographic dark-room trying to make a Hertzian oscillator work -presumably it was intended for use in the experiments on wireless waves already referred to. Rutherford had brought with him the “magnetic coherer” for the reception of Hertzian — or “wireless” — waves which he had invented while still a student in Christchurch. “Thus,” says Professor Eve, in recording this incident, “there occurred a fourfold coincidence: Bragg, Rutherford, oscillator and detector.”

Early Work in Adelaide on X-Rays

They say that the tame tiger, having once tasted human blood, becomes thereafter a dangerous man-eater. Bragg, in his experimental research on the alpha-rays, having once tasted the joy of discovery, similarly realised his true vocation, and from then on followed the gleam of his “one true light” to the end of his days.

As an initiation to experimental research the work on alpha-rays was well chosen. Here was a clear-cut problem to which experiment could and did yield a definite solution.

Once solved, however, and obviously related questions such as the stopping-power of the different species of atoms for the rays cleared up, he was content to leave it to others to apply the method to f ill in blank spaces and to elaborate refinements while he himself turned his attention to the more extensive field of the mysterious X-rays.

As already stated, Rontgen himself could do no more than offer a suggestion as to their possible character. A strong similarity to light was shown in the fact that X-rays travel in perfectly straight lines from point to point, in their power to ionise air or other gas, to affect the photographic plate and to cause certain minerals to emit fluorescent light. Yet an essential identity in their nature seemed to be excluded by reason the failure of all attempts to reflect them from the surface of a mirror or to bend their path by passing though a prism.

Even the possession of a wave-like character was put strongly in doubt by the apparent absence of two effects which are common to all kinds of waves, viz., the “interference” of one beam with another identical beam to produce a partial nullification, and the power of all waves to bend in some degree around an obstacle placed in their path, known as “diffraction”. On the other hand, if a corpuscular character were attributed to them, their pursuance of a straight path, undeviated by the influence of the strongest electric or magnetic fields, showed that they carry no electric charge, whether positive like alpha-rays, or negative like the beta.

Since in all the above respects — save only in far higher powers of penetration — the gamma rays of radioactive substances were identical, they too, were taken to be X-rays. The view generally held as to the nature of X-rays when Bragg commenced his researches was the “ether-pulse” theory proposed by Sir George Stokes, Lucasian professor of mathematics in the University of Cambridge. According to this, the violent impact of the cathode rays on a solid object would result in an electrical wave-pulse, much as the impact of a bullet on a target gives rise to a short sharp pulse of sound. Such a pulse, it was argued, would not possess the ability of a train of waves to exhibit interference or diffraction effects, nor to undergo reflection or refraction, but would still travel in straight lines with the speed of light and, it was claimed, possess the power to eject electrons from atoms on which it impinged.

It was in this last claim, especially, that Bragg from the first suspected a weakness which he set out to test by a series of experiments.

The experience gained in his work on alpha-rays stood him in good stead, for although there was no question of identity between these and X-rays, the same method of observation, namely measurement of ionisation produced by the rays in a gas, was applicable to both, and the essential equipment for such observation was ready to hand.

Also, Bragg was again fortunate in securing the valuable assistance of a capable collaborator in the person of John Madsen, a Sydney graduate who had been appointed to take charge of classes in electrical engineering under Bragg. Their experiments were directed towards the elucidation of the relations between the gamma-rays and the properties of the electrons ejected by them from atom on which they impinged. Reports of similar experiments made on X-rays by European experiments were already available in scientific literature.

The experimental evidence obtained by Bragg and Madsen confirmed Bragg in his doubts respecting the validity of the ether-pulse theory. It pointed with strong probability to a close equality of the energy of the ejected electrons with that of the gamma-rays which expelled them, and to a continuance of their motion in the same direction of travel, hence, Bragg argued, to a direct transference of the energy of the one ray to the other. Such a transfer of energy is easily understood on a corpuscular theory of X-rays — requiring nothing more to explain it than the mechanical laws of colliding bodies — but extremely difficult -to reconcile with any theory of an ever-expanding wave which, obviously, must disperse its energy over a wider and wider surface as it travels on, whereas the speed of ejection of electrons was found to be the same whatever the distance of the sheet of metal from the radium emitting the gamma-rays. Neither, as his experiments proved, did the nature of the metal, whether aluminium, or copper, for example, affect this speed in the least, a sufficient proof that the energy of the electrons was derived from that of the gamma-rays alone and not from a store of energy within atoms through which they passed.

Bragg clearly realised the need for explaining the enormous differences in penetrating power of the gamma and the beta-rays, and the indifference of X-rays to the action of electric or magnetic forces. His explanation was simple, and in the existing state of knowledge, highly plausible.

It was based upon what he termed the conception of a “neutral pair”. When a high-speed negatively charged electron penetrated an atom, it was assumed that it could pick up from the atom another particle charged with an equal amount of positive electricity which would, of course, neutralise its own negative charge, thus becoming electrically neutral and consequently relatively immune to the influence of both electrical and magnetic fields whether within atoms or without.

By the converse process, just as easy to imagine, of losing this positive partner in penetrating another atom, it would be possible for the X-ray to be reconverted to an electron, which on the assumption of negligible mass in the positive particle removed, would possess the same or nearly the same energy and speed as the original electron which created the X-ray.

Another consequence of the neutral-pair theory, on which Bragg laid stress was, as he believed, confirmed in the indirect mode of ionisation by X-rays. Naturally, if, due to the neutral character of an X-ray and consequent lack or weakness of its external field of force, at atom can exert little or no influence upon a ray passing through it, the X-ray in turn would exert little or no effect upon the atom.

Only when the positive part had become detached and the ray reconverted to a moving electron would its disruptive power come into play. Hence ionisation and the production of cathode-rays from X-rays must go hand-in-hand. This deduction is certainly well verified in the case of the most penetrating X-rays and all the better, of course, in that of gamma-rays whose properties — and especially their penetrating power — correspond to X-rays produced by several million volts.

But with the extension in range of penetrating power to include very “soft” X-rays, this argument loses all validity and the behaviour of X-rays is seen to fall into line with a general principle governing the exchange of energy between rays and atoms, illustrated also in the fact, already cited, that the ionising power of alpha-rays is at its maximum just at the end of their path.

Bragg’s ingenious neutral-pair theory did not pass unchallenged.

Dr. Charles Barkla of Liverpool attacked it in the columns of “Nature”, citing in refutation many experimental observations made by himself on the behaviour of X-rays, and claiming these as being entirely consistent with the ether-pulse theory and inconsistent with a corpuscular.

Bragg replied with equal vigour, stressing, naturally, the results on gamma-rays obtained in the Adelaide experiments.

Since future developments have shown that both theories are untenable it does not seem worthwhile today to assess the merits and demerits of the case either for the prosecution or the defence, but it is satisfactory to be able to report that both disputants have been subsequently awarded the Nobel Prize for their Aork in the very f ield on which they fought and that the award to one, at least, was in part due to the confirmation of his discoveries by the other.

In January, 1909, the Australasian Association for the Advancement of Science met it Brisbane and Bragg was its President. He chose as the title of his Presidential Address: “The Lessons of Radioactivity” and in it he gave a masterly and eloquent exposition of the state of knowledge in this new branch of science at that time. In evidence of his possession of a power of poetic imagination, I will quote one passage from this fine address verbatim. After emphasising the independence of radioactivity of all physical conditions, he goes on to say: “It is clear that we are dealing (in radioactivity) with the most fundamental characteristics of atoms, with the building material and not with the structure; with the inner nature of the atom and not its outside, and it is this which differentiates radioactivity from the older sciences. You will remember how Jules Verne in one of his bold flights of imagination drives the submarine boat far down into the depths of the sea. The unrest of the surface, its winds and its waves, are soon left behind; the boat passes through the teeming life below, down into the regions where only a few strange and lonely creatures can stand the enormous pressure, and driving still further, reaches at last black depths, where there is a vast and awful simplicity. Here ‘where no man hath come since the making of the world’ the silent crew gaze upon the huge cliffs which are the buttresses of the continents above. It is with the same feeling of awe that we examine the fundamental facts and lessons of the new science.”

It was inevitable, as Andrade says, that with his reputation as a physicist of the first rank now established, Bragg should receive offers from other centres of learning. An offer in 1906 to become the first Professor of Theoretical Physics in McGill University — one may suspect a Rutherfordian influence in this — was nipped in the bud by a fire which destroyed a great part of the University and upset its finances. But in 1908 came a second call to the Cavendish Professorship of Physics in the University of Leeds.

Bragg, eager to prosecute his research work with better facilities than were available to him in Adelaide — he told his colleague Mitchell that he anticipated that chemical analyses which took months to complete in Adelaide would be done in less weeks in Leeds — accepted, and left Adelaide with his family for England in February of the year 1909.

They travelled on the ill-fated ship “Waratah” — it was the return trip of her first voyage. On her second the “Waratah” disappeared without leaving a trace between Durban and Cape Town.

In a letter which Bragg had written to a friend (Sir Charles Todd) in Adelaide after arriving in England, he expressed very grave concern regarding the sea-worthiness of the ship, based in all probability, on the long time which was taken in recovering from a roll. It is a general principle of oscillatory motion of all kinds that such a slow recovery — in technical terms, a long period of oscillation — is an indication of an approach to instability. At the official enquiry into the loss of the “Waratah” the evidence to this effect given by Bragg helped to elucidate the cause of the disaster.

During the first two years of his stay at Leeds his published scientific papers dealt mainly with the same problem of the relation of X-rays to the secondary electrons ejected by them, or the converse effect.

No doubt the process of settling in with the work of preparing new courses of lectures, new practical courses, perhaps certain unexpected frustrations, limited the amount of time and energy available for taking up researches in new fields.

The situation in regard to the nature of X-rays — whether corpuscular or undulatory — seemed to have reached a deadlock.

Bragg’s “neutral pair” — a forecast of the actual “neutron” now known to exist — was satisfactory as an explanation of the extraordinary power of the rays to penetrate matter — far exceeded indeed by that of the real neutron — and, as Bragg was the first to maintain, of their inability to ionise gases directly and only by mans of the secondary electrons they create. Cn the other hand, the electro-magnetic wave or pulse-theory offered a more plausible explanation of the polarisation of the rays which, precisely as with light-waves, took place when the rays were scattered from matter through which they passed. An experimental proof that their velocity was identical with that of light would have been decisive for the wave-theory, but the claim made by a German scientist to have proved this equality was rejected by Bragg as unwarranted. The crucial tests for a wave-character, as already remarked, lie in the effects known as “diffraction” and “interference”. The situation was, in fact, a striking parallel to that which existed in regard to the nature of light in the time of Newton, 300 years ago.

Newton upheld the corpuscular view of the ancient Greeks on the very same grounds as Bragg for X-rays, namely the sharpness of their shadows and lack of evidence as to their capacity for interference or diffraction. His Dutch contemporary, Huyghens, on the other hand, espoused the wave-theory.

Only after Thomas Young in England and Fresnel in France had devised experiments which convincingly demonstrated the existence of these effects was the corpuscular theory abandoned in favour of a wave-theory.

Subsequent refinements and elaborations of such experiments has built up a vast body of precise information concerning light-waves and their properties and led to extensions of the realm of optics to include both waves too long and waves too short to affect the sense of sight — the “infra-red” and “ultra-violet” regions.

It was, at least, a reasonable ty-pothesis that waves of the same (electro­magnetic) nature might exist of still shorter wave-length than the shortest known ultra-violet.

On the other hand, even to convinced adherents of the wave-theory of X­rays, there seemed to be no prospect of determining the wave-lengths or obtaining a spectrum of the waves by means of an interference or diffraction effect, since estimates based on Stokes pulse-theory and on the failure of all experiments to find such an effect indicated a value of the wave-length 1000 times less than that of light. Thus, 17 years after the date of Rontgen’s discovery the true nature of the rays remained undecided. But in 1912 a discovery was made which not only solved this mystery but inaugurated a new era in the Department of Physics of the University of Munich, in this branch of science when Max von Laue, a Privat-dozent was inspired by a brilliant idea.

Laue’s Discovery; W.L. Bragg’s Interpretations; Joint Work of W.H.B. and W.L.B.

Laue’s special interest had been in the electromagnetic wave-theory of light. He had been entrusted with the task of writing an article on wave-optics for the Encyclopaedia of mathematical Science and in doing so had devoted special attention to the theory of the diffraction-grating. He was also well acquainted with the space-lattice theory of crystal -structure, a theory which explains the geometrical characteristics of crystal-form in terms of the arrangement of its atoms or molecules in a pattern which repeats itself throughout the whole volume of the crystal. Thus in a crystal of the cubic or regular system the elementary unit of pattern might take the form of a cube with an atom at each corner, a repetition of which in all directions could result in a crystal having its faces perpendicular to the edges of the cube. Assuming such a structure a simple calculation based upon a knowledge of the density of any crystalline solid and the weight of its molecules gives the average spacing of these as something of the order of one hundred millionth of a centimetre.

Now, although Rontgen himself and others after him had failed to obtain conclusive evidence of the diffraction of X-rays (e.g., in spreading out as light does after passage through a fine slit) yet others believed that photographs of a narrow beam of rays passing through a fine slit did indicate such diffraction. This was strongly confirmed when Koch of Munich devised a photometer which far surpassed the human eye in its resolving power. His measurements on photographs such as that just mentioned indicated a wave-length of one thousand millionth of a centimetre, that is about one-tenth of the spacing of the atoms in a crystal, a relationship comparable to that existing between wave-lengths of light in the visible range and the spacing of lines on a diffraction-grating.

To Privat-dozent Laue, equipped with these elements of knowledge basic to a solution of the problem but as yet held in separate compartments of his mind, there came one evening a student, P.P. Ewald, seeking assistance in his endeavours to solve a problem in wave-propagation concerned with the effect of a three-dimensional space-lattice on electromagnetic waves passing through it.

Laue confesses that he was unable to help Ewald to solve his problem. But the discussion effected the necessary conjunction of hitherto separated conceptions. He says “The idea came to me to put the question: how would waves behave which are short in comparison with the spacings (of atoms) in a space­lattice? My optical sense furnished an immediate answer. Diffraction spectra must result.” Despite adverse comment by his seniors on the staff he obtained permission to put this opinion to the test of experiment. Two young assistants were employed to set up a simple arrangement for this purpose. A fine pencil of X-rarys, limited by passage through pin-holes in lead sheets, traversed a thin plate of a copper-sulphate crystal and fell upon a photographic plate. After a few failures, due to erroneous placing of the crystal, the anticipated result was obtained. Surrounding the central spot due to the direct ray were several faint replicas which could only be due to diffraction effects. The evidence was conclusive. At one stroke both the wave-theory of X-rays and the existence of the crystalline space-lattice had found convincing confirmation.

Further experiments were then made — all critics silent now — with refinement in the details of the apparatus and on several crystals of a simpler type, including zinc sulphide, which belongs to the regular or cubic system. Beautifully symmetrical patterns of spots were obtained, the position of which on the plate could be correlated with three whole numbers (replacing the single number in the equation connecting wave-length and direction of diffracted beam in the theory of the one-dimensional grating) each set specifying a set of atoms in the crystal which collaborated in their scattering effects in a certain direction.

For complete correlation, however, of theory and results, an assumption had to be made as to the nature of the elementary unit of pattern in the space­lattice.

Von Laue’s assumption of a cube with an atom at each corner was erroneous and to get even an imperfect agreement between his calculations and actual measurement necessitated an arbitrary restriction of the wave-length of the rays to certain specific values.

It was at this stage, that William Lawrence Bragg took up the running. He was at that date (1912) a research student in the Cavendish Laboratory at Cambridge and, as he states, “an ardent supporter of my father’s views respecting the corpuscular nature of X-rays.” He goes on to say: “During the summer of 1912 we had discussions on the possibility of explaining Laue’s pattern (of spots) by some other assumption than that of diffraction of waves, and I actually made some unsuccessful experiments to see if I could get evidence of “X-ray corpuscles” shooting down the avenues between the rows of atoms in the crystal. On returning to Cambridge to ponder over Laue’s paper, however, I became convinced of the correctness of his deduction that the effect was one of wave­diffraction — but also convinced that his analysis of the way it took place was not correct.”

He then proceeds to explain how from a certain secondary feature of the photographs (merely, in fact, the change in shape of the spots with position on the photographic plate) he was led to substitute the idea of a reflection of the rays by planes more or less densely packed with atoms for the scattering of waves from individual atoms on which Laue based his explanation. Also, he found it necessary to replace Laue’s simple elementary cube by one in which an atom was situated not only at each corner but in the centre of each face (an arrangement which had been proposed on other grounds by Professor Pope of Cambridge).

Repeating now the calculation with the necessary modifications he found complete agreement with the observed pattern and thereby decisive proof of the essential correctness of Laue’s theory. (Thus, nobly, do the rival galdiators in the arena of scientific research come to the help of an opponent who stumbles!)

There followed immediately upon his initial success similar solutions of the X-ray diffraction spectra of several other simple kinds of crystalline salts. The first day of success in the X-ray method of analysing crystal structure had dawned, to be followed, in perennial succession, by thousands of others.

The younger Bragg, in these initial stages, had also at first regarded the space-lattice of the crystal as a regular arrangement in space of individual atoms and used the same method of mathematical analysis as Laue to obtain a picture of that arrangement. But what might have seemed to anyone else an unimportant minor feature of the photographs (as already mentioned it was a change in the shape of the diffraction images with increasing distance of the image from the crystal) led him to an alternative and most illuminating viewpoint. It was to regard the atoms as lying in sets of parallel planes, in analogy to the way in which the vines in a vineyard may be seen as arranged in parallel rows. And just as by changing the direction of observation in the latter case different sets of rows appear in view, so, in a crystal, a multitude of sets of planes, each set packed more or less densely with atoms, intersect it in varied orientation.

When a beam of X-rays penetrates the crystal a swarm of secondary wavelets starts out f rom each and every atom in an atomic plane each time a wave passes over them the aggregate of these forming a new wave-front. Alone, such a secondary wave oould be feeble far below the possibility of detection. But if, as may result from a particular relation between the spacing of the planes, the wave-length and direction of travel of the rays, the reflected waves from successive layers follow one another crest upon crest and trough upon trough — to use a metaphor drawn from water-waves - then their cumulative effect could well be expected to amount to a reflection comparable in strength to the reflection of light from the most perfect mirror. on this being pointed out to him by the distinguished physicist C.T.R. Wilson (inventor of the fog-chamber method of detecting tracks of alpha and other corpuscular rays) Bragg (jnr.) immediately made the experiment of directing a pencil of X-rays on to a thin sheet of mica and placing a photographic plate in a position to receive both incident and reflected ray.

When the angle of incidence was rightly adjusted, an exposure of a few minutes only sufficed to show the existence of the predicted effect whereas to obtain Laue diffraction-pictures of comparable intensity an exposure of several hours was required. Here, then, was obviously a new and powerful tool of X-ray analysis, and one moreover which could be made to serve a double purpose. Firstly, from the relation between wave-length and direction of travel of the waves and spacing of planes, a knowledge of wave-length would enable a determination of the spacing; secondly, if the spacing is known it is only necessary to measure the angle at which reflection occurs to find the wavelength.*

* The relationship of the spacing of the atomic planes in the crystal to the wave­length of the X-rays and the angle at which they impinge on the planes is expressible by a simple equation known as “Bragg’s Law”.

The elder Bragg (to whose work on X-rays after this long digression we now return) immediately recognised the truth and appreciated the possibilities revealed by Laue’s discovery and his own son’s interpretation of it, without, however, wholly renouncing his previous arguments in favour of a corpuscular theory. His acceptance of the wave-theory was hailed by Arnold Sommerfield in these wards, written in 1913 in the course of an appreciation of Laue’s discovery: “One particularly admirable success of these crystal diffraction photographs is the service they have done in convincing the most renown adherent of a corpuscular theory — W.H. Bragg — and bringing him over into the camp of the followers of the wave-theory.”

It was true that Bragg, confronted with the compelling evidence of these new phenomena, could not but accept the wave-theory. But, as remarked above, he did so with a reservation. In November of 1912 he expressed his views on the matter as follows: “Dr. Tutton suggests that the new experiment may possibly distinguish between the wave and the corpuscular theories of the X-rays. This is no doubt true in one sense. If the experiment helps to prove X-rays and light to be of the same nature then such a theory as that of the ‘neutral pair’ is quite inadequate to bear the burden of explaining the facts of all radiation. On the other hand, the properties of X-rays point clearly to a corpuscular theory and certain properties of light can be similarly interpreted. The problem then becomes, it seems to me, not to decide between the two theories of X-rays but to find, as I have said elsewhere, one theory which possesses the capacity of both.”

Here Bragg enunciates clearly the outstanding paradox of modern physics, the possession by the same physical entity of two apparently irreconcilable characters: wave and corpuscle. It would seem probable that he was not fully aware of the developments which had been taking place in Germany — paralleling his own independent line of thought — following upon the discovery in 1900 of the discontinuous nature of temperature-radiation by Planck, and particularly of Einstein’s attribution of a corpuscular aspect to ordinary light — shared with its wave-character — according to which the frequency of the waves fixes the energy of the corpuscles, and which have culminated in the mathematical theory of wave-mechanics. Be that as it may, he immediately appreciated and prepared at once to apply the reflection of X-rays by crystals in experimental investigations. His interest at the outset — as Sir Lawrence has informed me — was directed, not so much towards the determination of crystal structure — which perhaps he regarded as his son’s pre-emptive right - but to the reciprocal problem of defining the quality of X-rays in terms not, as formerly, by their power to penetrate or to be absorbed by matter but of their wave-characteristics, namely, wave-length or frequency and intensity.

To this end he devised a beautiful instrument, the X-ray spectrometer (the counterpart of the optical spectrometer used in the analysis of light in the visible, infra-red or ultra-violet regions) which can be employed to weasure not only wave-lengths like the optical instrument but also intensity of X-ray beam. The manner of using it is as follows: A beam of the radiation to be examined is defined in direction by passage through narrow slits in sheet-metal, falls then upon a plate of a perfect crystal — rock salt, calcite or other — which can be rotated in such a way as to throw a reflected beam into an ionisation chamber. The angle made by the atomic reflecting planes in the crystal with the incident beam then gives the wave-length; the value of the ionisation current the intensity.

Sir Lawrence Bragg writes about this instrument as follows:-

Moseley’s famous experiment of a year later in which he determined the wave-lengths of the X-rays characteristic of a series of chemical elements was a direct extension of these earlier experiments of W.H. Bragg, the main difference in his technique being the substitution of a photographic plate for the ionisation chamber. The elder Bragg’s one incursion into crystal analysis -which his son was pursuing concurrently with equal vigour and success — solved the problem of the arrangement of atoms in the diamond, a crystal, it need hardly be said, unique in many of its physical and optical properties. The dimension of the unit cell of its space-lattice — built up of tetrahedra with a carbon atom at each corner of each tetrahedron and one at the centre — is defined by one single length, viz., the distance from every carbon atom to anyone of its four neighbours. This distance is 1.54 Angstrom units.

It is not difficult to appreciate how the remarkable properties of diamond — its extreme hardness and elasticity, its infusibility and insolubility (which have, up to now, frustrated attempts to make artificial diamonds) its high refracting power for light, find a physical basis in such a structure. The tetrahedral character assigned by chemists to the carbon atom which is one of the key-stones of structural organic chemistry is visibly apparent in this model. Another feature, common to carbon compounds of the aromatic class, of which benzene is the simplest exemplar (equally put in evidence in this crystal model) is the existence of a linked meshwork of rings in each of which the atoms lie alternately either slightly above or slightly below a median plan.

The other crystalline form of pure carbon known as graphite differs most remarkably from diamond in many ways - among others in its opacity to light, and in its power of conducting electricity like a metal. The explanation of this difference is to be seen it is space-lattice in which the benzene-ring layers are now separated much more widely, so that rigidity, as between them, is lost and the crystal flakes easily along these layers, behaviour which explains well its property as a lubricant.

World-War 1. Work on Submarine Detection

This period of intense and fruitful co-operation of father and son was interrupted by the outbreak of the first World War.

To combat enemy submarine attacks on British shipping, the Admiralty had created a Board of Invention and Research for the purpose of obtaining scientific advice on methods which might be devised for countering this menace. Bragg, an original member of this Board, was appointed “Director of Research on methods of detecting underwater sound,” the objective being to locate enemy submarines either by the self-emitted sound of its screw-propeller or engines or (as proved to be far more effective) by the echo from the hull of the submarine of a pulse of sound-waves generated by some form of transmitter carried on a destroyer.

(Water, even when so turbid that a beam of light is transmitted only a few feet, is an excellent medium for sound-propagation.)

Experimental work was carried on, in the first place at a naval base on the Firth of Forth; afterwards, when this proved unsatisfactory, at Harwich. Ernest Rutherford was also an active collaborator in this work.

A small team of physicists and technicians worked under Bragg’s direction on the problems of devising sound generators for creating an intense bean of high-frequency sound waves on the one hand and receivers suitable for detecting the echo reflected from the hull of the submarine, on the other.

For the former, a modified form of the piezo-electric vibrator devised by Professor Langevin of Paris, was employed; for the latter, underwater microphones or hydrophones. Success was finally achieved in constructing these in such a way as to indicate nor merely the arrival of the underwater sound from a distant source but in indicating the direction from which it came.

While Bragg the father was engaged on this work, Bragg the son was employed upon the parallel problem of locating the position of the eneny’s heavy guns by somewhat similar mans, namely the precise times of arrival of the sound­wave which accompanied the firing of the gun at several different stations behind the British lines. Here again, a special type of microphone (Tucker hot-wire microphone) was devised which discriminated in favour of the explosive wave arriving from the distant gun as against local noises.

During his stay at Lees a tempting offer had come to Bragg in the form of an invitation to become the Principal of the new University of British Columbia. In some uncertainty of mind as to whether or not he should accept, he sought the advice of his friend Rutherford.

Rutherford’s reply to the inquiry is so characteristic of his outlook that I quote a couple of sentences. “I think,” he says, “that if I were tired of physical work (does he not mean ‘work in physics’?) and had not an idea left to work on, I should consider it an admirable position to occupy one’s declining years, but I quite agree with you that it would be very difficult to leave the Physical ;-brld (world of research in physics?) at such an interesting time when there is so much to do and so many interesting problems in sight.”

With such a hint that, in Rutherford’s opinion, administrative jobs are suitable occupations for scientific men only when approaching senility or when vacuity in ideas renders them incapable of further productive work it is not surprising that Bragg declined the position.

But, when in 1915 he was invited to become Quain professor of physics in University College of London University, he accepted, and as soon as release from war-service cam with the ending of the war, resumed his work on crystal analysis. Many other physicists and crystallographers, both in England and elsewhere, impressed with the power of this new weapon - so conclusively demonstrated by the Braggs — began to make use of it in the same field of research.

Many modifications in the method of crystal analysis and many extensions of its application, resulted from their work. of these, the most important was due to Bragg himself, when in 1924 he showed that bymaking a bold yet plausible assumption the principles and technique of the X-ray analysis of crystal structure could be applied to the determining of the structure, not only of inorganic but also of organic crystals — or, at least, of that large class known as aromatic compounds.

The assumption is that the group of six carbon atoms linked together to form a hexagon known as the “benzene-ring” (benzene itself consisting of such a ring plus six hydrogen atoms) may be regarded as a physical ent1ty of definite size and form irrespective of the crystal in which it occurs. Thus naphthalene is to be looked upon not as a molecule containing 10 carbon and eight hydrogen atoms but as two benzene rings having one side - or two carbon atoms — in common. Bragg demonstrated the value of this hypothesis by the experimental determination of the form and dimensions of the unit-cell, the infinite repetition of which builds up the crystal — of a number of benzene and naphthalene derivatives and it has since been successfully applied by others to compounds of such extreme complexity as the proteins.

Director of the Royal Institution

The Royal Institution of Great Britain, most famous of all scientific foundations, of which it has been well said “that it combines the characteristics of an academy, a college, a research institution and a club” was founded in the year 1799 by that extraordinary individual Count Rumford (born plain Benjamin Thompson, at the little town of Rumford, in the State of Massachusetts).

Exiled from his native land because of his active partisanship of the British cause in the American War of Independence, knighted by King George III for his services in military administration, created a Count of the Holy Roman Empire by Karl Theodor, Elector of the State of Bavaria, in recognition of the social and military reforms which he effected; soldier, administrator, scientist, inventor and social reformer; Rumford founded the Institution “for the promotion of science and the diffusion and extension of useful knowledge.”

Well has it served those worthy aims. From within its laboratories in Albermarle Street, Piccadilly, under the direction of a succession of famous scientists, there has come a succession of famous discoveries. In its lecture­theatre these same men and many others of scientific fame have expounded the most recent advances in their special field of knowledge.

Its first director, Humphrey Davy — famous for adding sodium, potassium, chlorine and iodine to the list of chemical elements and for his invention of the miner’s saftey-lamp — by his enthusiasm and eloquence, drew to his audience not only the few engaged in serious scientific pursuits, but also the many to whom his discourse merely offered intellectual entertainment. His successor, Michael Faraday, greatest of experimental scientists, rose to that dignity and fame from the humble level of Davy’s laboratory assistant; as an expositor of science he rivalled his former master.

Daring Faraday’s regime the finances of the Institution, hitherto always precarious, were greatly improved by a benefaction by John Fuller, a wealthy -and, it is said eccentric — Member of Parliament. This enabled the managers to create two “Fullerian” Professorships, one in Chemistry, the other in Physiology; to these a third, in Natural Philosophy was subsequently added. Faraday was the first “Fullerian” Professor of Chemistry.

John Tyndall, who followed Faraday, made important contributions to our knowledge of Radiant Heat, of Light and of Sound. He, like his predecessors, combined the faculty of speaking well with that of writing well. His books on Sound, Light and Heat still repay reading by students of Physics.

Next in succession came Sir James Dewar, well-known for his success in liquefying hydrogen gas for the first time and for invention of the Dewar vacuum flask, better known by its commercial title of “Thermos”. Dewar died in 1923 after holding office for 46 years.

The task of choosing a successor was probably not a difficult one. Bragg was clearly marked as the right man. He had all the essential qualities demanded of the occupant of this distinguished office in full measure: the ability to originate, prosecute or direct fundamental research; the gift of simple yet inspiring oratory; a personality richly endowed with dignity of bearing, sincerity of speech and charm of manner.

He was elected to the combined offices of Director of the Royal Institution, Resident Professor and Fullerian Professor of Chemistry. To these was added a new responsibility — Director of the Davy-Faraday Research Laboratories, the construction, equipment and maintenance of which was made possible by an endowment which the Institution received from Dr. Wdwig Mond. This fund also permits the financing of a limited number of independent research workers.

Bragg brought with him for inclusion in this band of coworkers, two members of his University College staff, Messrs. Muller and Shearer, both already experienced in the technique of X-ray crystal analysis. These two, especially, gave valuable assistance in the design and construction of new and more powerful equipment, which included, for example, two high-power X-ray generating tubes, one of 5 k.w., the other of 50 k.w.

These and other improvements permitted a reduction in the time required for the observations to a fraction of what it had previously been.

An active school of research in X-ray crystal analysis soon came into being. In its members are included such well-known names in British science as J.D. Bernal, W.T. Astbury, Kathleen Lonsdale, and many others who have made important contributions to this new branch of science.

While the steady flow of publications describing the results of these researches amply fulfilled the primary purpose of Count Rumford’s foundation, the “promotion of science”, it did not supplant or prevent the fulfilment of its secondary objective, “the diffusion and extension of knowledge.” Increase in membership and in the numbers attending lectures necessitated extensive alterations and additions to the Lecture Theatre, Library and reading room of the Institution. The Friday evening discourses initiated in Faraday’s time received fresh accession of popularity largely because of the attraction exerted by Bragg’s own lectures and demonstrations.

When conversaziones were held, to which large numbers were invited, lady Bragg was, as formerly in Adelaide days, an active assistant to her husband in explaining exhibits and experiments to visitors.

On this wifely occupation her sister (Miss Todd, makes the following comment: “He and I would listed with great enjoyment to my sister explaining experiments to her friends and he would smile at me with delight and understanding.” I once said to her, “How can you dare to do this, especially with Will listening, when you really don’t know a thing about it?” “Well, darling,” she would reply, “they understand what I tell them far better than when will explains.”

This very human gift for entertaining and interesting people was a great help to my brother-in-law all through his career. They were a much-loved pair in the university town of Leeds and, when at the Royal Institution in London, my sister made an excellent hostess. She still, at the Friday night receptions, would explain the experiments, and I used to think that the more inexact she was, the more the group round her would enjoy themselves.”

Bragg’s first successful course of “Christmas Lectures to Children” in the ‘World of Sound” was followed by several others: “Old Trades and New Knowledge” — designed to demonstrate “the way in which new knowledge is continually changing the old crafts”; “Concerning the Nature of Things” (a modern version of “De rerum Natural’ written by the Roman poet Lucretius 2000 years ago, devoted not to his object of “freeing mankind from fear of the supernatural” but merely to an explanation of their physical properties in terms of their atomic structure; and the “Universe of Light,” the theme and scope of which is well indicated in its opening sentence “Light brings us news of the Universe.”

When the Second World War broke out in 1939, Bragg at the age of 76, was not too old to serve the nation as Chairman of the Advisory Committee to the British Government on Food Policy.

A letter which he wrote to the London Times shows no diminution of his power of clear and vigorous expression. His last public activity would appear to have been the organisation of a series of broadcasts by the British Broadcasting Corporation in collaboration with the Science Committee of the British Council -of which Bragg was Chairman — entitled “Science lifts the veil”. I quote from the preface to the published edition of these tasks:-

“The late Sir William Bragg .. was deeply interested in the series. He believed enthusiastically in the great role that broadcasting must have in the stimulation of public interest in and the understanding of science. He proposed the theme for the series, sketched the topics and gave the opening talk himself . He introduced ten of the speakers, including his own son, Sir Lawrence Bragg, and his last public words were spoken in his discussion with Professor J.D. Bernal on ‘The Problem of the origin of Life.’”

This most interesting discussion is too long to quote in its entirety. But in order to put these last words spoken by Bragg in public on record here, as well as for their intrinsic interest, I reproduce the last few questions asked and the answers given.

The discussion has turned upon the structure of protein molecules — a problem Bernal had been foremost in attacking by the method of X-ray analysis -and especially of the nature of a virus, probably the lowest thing to which the quality of life can be assigned.

Bragg asks: But if one protein or virus must always come from another how did the first one get there? How did it all start?

Bernal answers: That’s what we have to find out. One big step towards it is getting the structure of virus and protein molecules. it’s really the problem of the original life.

Bragg: That is just it. What do you mean by life? All the time you have been talking of a virus as alive at one moment and being a crystal at another. How can that be?

(It is now Bernal’s turn to put the question) . He asks: Well! What do you mean by “life”?

Bragg replies: When I was young it seemed quite simple. A thing was alive if it moved and grew and reproduced its like. Crystals did not move or reproduce. They did grow; not like a living thing by taking outside materials into themselves but simply by adding more on the outside like piling stones on a pyramid. Now your viruses don’t move. They can’t grow by taking material inside themselves because they have not got any insides, but they do seem to reproduce. Are they alive or (are they) not?

Bernal: I would prefer not to say.

Bragg: Why not?

Bernal: Because my colleague Dr. Pirie who had done so much of his work on viruses and has written a cutting essay on the meaninglessness of the term “life” would never let me hear the end of it.

Bragg: But you must have some idea of your own.

Bernal: I have; but it’s no question of definition.

Bragg’s Religion

Brief reference has already been made to a painful episode in Bragg’s early life due to a revolt of conscience against those clauses in the Apostles creed which condemn all unbelievers to an eternity of existence in everlasting fire. A quotation from his autobiographical notes shows how deeply his mind was shaken in the struggle to free itself from the chains of beliefs, fastened upon him in early childhood. “It really was a terrible year,” he says. “For many years the Bible was a repelling book which I shrank from reading.”

This early experience lends a special interest to the discussion of his views on religion when matured by experience and based upon his independent judgment.

In 1941 he was invited by the University of Durham to deliver one of the annual Riddell Memorial Lectures — a foundation which honours the memory of the Scottish religious poet, Henry Scott Riddell.

The title he gave to his address was “Science and Faith”; its keynote is an endeavour so to interpret the meanings of these two words as to make compatible one with the other.

Defining “Science” in the first place as a “collection of observables of Nature” he proceeds to elaborate this definition by pointing out that to make the vast body of knowledge included in it comprehensible, the scientist must “endeavour to find (in it) correlations, rules and laws. He must reduce his observations to order, because he then finds indications of the most hopeful lines of further advance.

“He could not grasp what he has already got unless he did what he could to codify it. He therefore makes hypotheses.” (Here, by the way, is apparent contradiction to Newton’s much quoted declaration “Hypotheses non fingo”.) “But it is to be observed,” he goes on to say, “that all such hypotheses are tentative and are to be amended as knowledge grows.” He is insistent also that a clear distinction must be made between “science”, so defined, and “the applications of science” and that the reproaches made against science for the evil uses of some of its applications are misdirected.

Again and again he returns to emphasise the provisional character of scientific hypotheses and takes pains to illustrate this character by reference to the amendment which Einstein made in Newton’s Law of Gravitation and to the remarkable alternations which have taken place in our views as to the nature of light.

Seeking now a definition of “Faith” he quotes St. Paul: “Faith is the substance of things hoped for, the evidence of things not seen.” But while giving praise to this as “a sentence obviously full of earnestness and meaning” he acknowledges that it may mean different things to different people, for he goes on to say “When we look into the definition we find that we way not take it word for word without stripping it of all meaning.” My own interpretation,” he adds, “is that St. Paul’s faith was a hypothesis so firmly held and trusted that he would and did stake his life upon it. But he is describing a hypothesis which, like any other, exists to be tried by experiment. That need not trouble any follower of the rule of Christ because Christianity is again and again defined as an experimental religion.”

We see here that his aim is to justify Faith in the realm of religion on the same ground as he would justify it in the context of science, viz., in justification by results. It is at least a generous attempt to find a basis for the reconciliation of the two great modes of interpreting human thought and existence. But does it not ignore the existence of the deeper philosophical antithesis in their outlook, the scientific seeking always to make a picture of the world from which subjective and anthropomorphic aspects have been eliminated; the religious based on a presumption of intelligibility, meaning and purpose in the world which is relative to man’s existence and nature.

Irreconcilably opposed as these view-points may appear to be — and the history of the conflict of science and religion bears tragic testimony to the violence of human feeling engendered by this antagonism — we can all agree with Bragg that in the community of civilised educated humanity today, there is on either side a trend towards a less dogmatic assertion of doctrines which previously have been held as incontrovertible and absolute.

Bragg relates as an illustration of such a change in dogmatic theology the following experience of his childhood days.

“When I was a very small boy the maid in our house took my cousin and myself one Sunday to a service in the Independent Chapel of our town. We were a Church household and my grandmother, who was in charge of us, was much disturbed. in the evening she set us down to be questioned. She went through the item of the Apostles Creed. Did we believe in the Communion of the Saints? Did we believe in the forgiveness of sins? Did we believe in the Resurrection of the Body? And so on. Quite overawed we meekly answered “yes” to each question in turn. Finally, my grandmother closed the prayer-book, saying that she thought we must be all right. We had come to no harm.”

“Surely,” is his comment, “such an incident would be far more unusual now.”

“Religion,” says Professor Andrade in his obituary, “was a strong influence in Bragg’s life.” In a particular sense of this word like Faith, of marry meanings — the greater Oxford dictionary gives fifteen of the first and six of the second — this is doubtless true. Although Bragg has nowhere to my knowledge explicitly defined that sense we get some clues to it both from his comments of his early experiences and from other writings or utterances.

In the concluding paragraph of his “World of Sound” he contrasts Religion with Science: “in all our lives, in all we work and strive for it is of first importance to know as much as we can about what we are doing, to learn from the experience of others and, not stopping at that to find out more for ourselves so that our work may be the best of which we are capable. That is what Science stands for. It is only half the battle, I know. There is also the great driving force which we know under the name of religion. From religion comes a man’s purpose, from science his power to achieve it. Sometimes people ask if religion and science are not opposed to one another. They are: in the sense that thumb and fingers are opposed to one another. It is an opposition by means of which anything can be grasped.”

Here, again, the identification of religion with the motivating agent in human activity is broad enough to include not only the thousand and one “religions” which mankind professes today but a multitude of other spiritual agencies, not usually so classified.

It need not be doubted, however, that Bragg had Christianity chiefly in mind: a Christianity devoid both of theological dogma and of submission to any specific authority of man, church or book — he declined, much though it hurt him to refuse the request of a friend, to read the lessons at the open air services held by the Vicar of Leeds, saying “it would be a vindication in public of something he could not believe because it could not be proved.”

As to what is specifically implied in Christianity his own Words are these: “If a man is drawn towards honour and courage and endurance; justice, mercy and charity let him follow the way of Christ and find out for himself that it leads him the way he should go.”

Honor and Obituary

The scientific importance of Bragg’s work was recognised in the bestowal of many honours and awards by scientific societies and foundations. Election to fellowship of the Royal Society of London followed soon upon his earliest researches on alpha rays and X-rays; he became a member of its Council in 1911, vice-president during the years 1920, 1921 and again during 1923, 1924, 1925. He held the Presidency from 1935 to 1940. The Society’s Rumford Medal was awarded to him in 1916 for his contributions to the science of radiation, and the Copley Medal in 1930. He was President of the British Association in 1928.

In 1915 the Nobel prize for Physics — an award of the monetary value of about £110,000 made without respect to nationality, sex, or creed — was shared with his son in recognition of their joint creation of the new sciences of X-ray spectrometry and crystal analysis.

Knighthood in 1928 came in recognition of his service to the National cause as well as his scientific eminence. The supreme Civil honour of the order of Merit was bestowed in 1931. Concerning this last Miss Todd relates the following incident. A train traveller reading of the award in his morning paper remarked to his companion: “I see that Sir William Bragg has got an O.M.” To which the other rejoined: “Oh! Really. Does he drive it himself?”

Of many personal tributes paid to him during his life and after his death I will reproduce two only here.

The first is in the form of two elegant verses taken from the dedication of Professor Andrade’s little book on “Engines” (the record of a course of Christmas lectures to juveniles at the Royal Institution):

I quote one other tribute from the distinguished American physicist, Dr. Albert Hull, late Assistant-Director of the G.E. Co’s. Research Laboratory, and personal friend of the writer. He writes to me as follows:-

Bragg died peacefully after a very short illness on March 12, 1942. Although his physical strength had been declining for some time previously he remained mentally active and sufficiently interested to take part in a discussion on a point relating to the reflection of X-rays by crystals only a few months before he died.

A Memorial Service held in Westminster Abbey was attended by a great concourse comprising not only personal friends and associates but representatives of the King, Government Departments and all the leading Scientific Societies. The service was conducted by the Archbishop of Canterbury and the Dean of Westminster. His body by the wish of the family was interred in the grounds of the Church at the village of Chiddingford in Surrey where he had a country cottage.

Long before he died Bragg’s work had won world-wide renown. He belongs for all time to the company of those whose fame raises them far above all distinctions of nationality, race or creed. Yet perhaps it is still permissible for us in Australia to feel a special pride in the fact that his experimental genius first bore fruit on Australian soil.

The plea so often urged that our geographical remoteness from the centres of creative science in the older continents of Europe and America is a handicap to young men who aim at a career in scientific research work finds no more support from his judgment than from his performance.

On the contrary — as he once told me — he looked upon his own stay in Australia as a factor in his subsequent success and wished that many other of England’s young scientists could enjoy the same advantage.

His first experimental result (that all alpha-rays coming from the same radioactive element have a definite range) may seem unimportant in comparison with the extensive and important developments which have resulted from the discovery that a crystal reflects X-rays according to a definite law. Yet it too may be regarded as the starting point of a chain of discoveries culminating in one of portentous significance for the future of mankind.

For it was on this fact that Rutherford was able to discriminate between rays emanating from the radioactove sources and such as resulted from internal atomic energy released by their impact; from this first artificially induced atomic explosion a sequence of others culminated with the discovery of the nuclear fission of uranium, the motive agency in the atomic bomb.

Logically, therefore, the origin of the present international world situation may be followed back to the day when in a small basement-room of the University of Adelaide, William Henry Bragg first obtained the evidence that rays from radium travelled through air into which they emerged just “thus far and no further.”