Bertram Hopkinson

Professor Bertram Hopkinson, C.M.G., M.A., B.Sc., F.R.S. (1874-1918)

Author(s): T. M. Charlton

Source: Notes and Records of the Royal Society of London, Vol. 29, No. 1, (Oct., 1974), pp. 101

Obituary Notices of Fellows Deceased

Source: Proceedings of the Royal Society of London. Series A, Containing Papers of a

Mathematical and Physical Character, Vol. 95, No. 673, (Jul. 15, 1919), pp. i-xxxvi

BERTRAM HOPKINSON, who was killed in a flying accident on August 26, 1918, while engaged on national service, was born at Woodlea, Birmingham, on January 11, 1874. He was the eldest child of Dr. John Hopkinson, F.R.S., born when his father, then only 25 years old, was at the threshold of a career which was to achieve great things in science. At that time John Hopkinson, but lately Senior Wrangler and Smith's Prizeman, had accepted a responsible position with Messrs. Chance Brothers, and was applying his scientific skill to the task of improving the quality of their optical glass and developing its uses, especially for lighthouse illumination. The position enabled him to marry: his wife was Evelyn Oldenbourg, a lady of remark- able gifts, to whom he had become engaged almost immediately after he left Cambridge. Bertram was the eldest of a family of six, three boys and three girls. When he was three years old the family moved to London, where John Hopkinson took up professional life as a consulting engineer and inventor. This he pursued with conspicuous success until his premature death by an Alpine accident in 1898. Bertram owed to his parents far more than a heredity which was at once sound and of brilliant promise. The home atmosphere could not have been more congenial or more stimulating for a boy born with scientific tastes and richly endowed with mental and physical activity. John Hopkinson's absorption in invention and discovery never stood in the way of companionship with his children. He was in a rare degree his children's friend, and to Bertram especially this friendship was in itself a liberal education. The boy was no doubt extraordinarily receptive. From early childhood he was the almost constant associate of his father, sometimes assisting him in work, often his comrade in play. He lived at home, going as a day-boy to St. Paul's School, and enjoying intensely his father's company in the hours spent out of school, joining in long walks, in discussions, in experiments. Always strong in body and mind, he could profit by such a life without being over-strained. He prospered at school, was the youngest boy in his mathematical form, and secured a major scholarship at Trinity before he was seventeen. By that time he had imbibed not only much science and engineering, but the habit of scientific thinking and of applying scientific thought to real problems. In the researches he was to publish later, one sees at every turn the reflection of his father's mind. From his father, too, and scarcely less from his mother, he acquired a wholesome love (which he never lost) for most kinds of open-air activity. Walking, climbing, rowing, sailing, skiing, chamois-hunting in the Tirol, in such things he spent his holidays with the keen pleasure of one who was immensely alive in every- thing he undertook. At Cambridge he read for the Mathematical Tripos, which by that time was divided into a first and second part. In the first part he was compelled to content himself with an segrotat degree. An unlucky attack of illness-a rare event with one so robust-prevented his taking the examination; but next year, in the second part, his quality was shown by his being placed in the First Division of the First Class. For the rest his University life was normal and uneventful. He made some lasting friendships, and was one of a Trinity crew at Henley. On leaving the University at the age of 22 he proceeded to read for the Bar, a profession with which his father was connected by often serving as an expert in patent actions, and in which Bertram could count upon useful introductions. After working in counsel's chambers, where he was soon recognised as a pupil of distinction, he was called to the Bar in 1897. Next year he was on his way to Australia to carry out a legal enquiry, when the tragic death of his father, his brother, and two sisters changed the course of his life. The family were spending their holiday that autumn in Switzer- land, at Arolla, where Bertram joined them for a few days before taking ship to Australia. The days were spent in climbing expeditions, which included a traverse of the Matterhorn, after which Bertram went off to pursue his journey, and his father returned to Arolla. A few days later, John Hopkin- son, with three of his children, was killed in climbing the Petite Dent de Veisivi. A telegram recalling Bertram reached him at Aden. Faced with this calamity, Hopkinson decided to take up, so far as he could, his father's unfinished work. He joined in partnership with his uncle, Mr. Charles Hopkinson, and his father's valued assistant, Mr. Talbot, and with them, was responsible for the design of electric tramnways at Crewe, Newcastle, and Leeds, as well as other works. To do this required courage, not to say daring: in that he was never wanting. It required, too, a rare adaptability, and perhaps was possible only because of the irregular and almost unconscious training in engineering which he had received from his father. An important element in his life at the time was his intercourse with Sir Benjamin Baker, who had been for many years a close friend of the family. Sir Benjamin appreciated Bertram, enjoyed scientific discussion with him, and remained, until his death in 1907, an intimate and most helpful friend. Hopkinson not only succeeded in the practical aspect of his new under- taking, but soon found in it material for scientific research. A paper by the three partners on "Electric Tramways," read before the Institution of Civil Engineers in 1902, gives particulars of his experiments on the electrolysis of pipes and other matters arising out of their engineering work. For this he was awarded a Watt Gold Medal by the Institution, of which later he became a full member. In 1903 the chair of Mechanism and Applied Mechanics in the University of Cambridge became vacant. Hopkinson was then only 29 years of age, and so far as teaching was concerned he was wholly untried. But already he had a considerable professional reputation, and lie gave a personal impression of brilliancy and promise which satisfied the electors. In electing him they certainly made a wise choice, and were entirely justified in the result. The professorship meant his assuming charge of the Cambridge Engineering School, which by that time had become an active and considerable section of the University. Its expansion had been rapid from about 1892, when the Mechanical Sciences Tripos was established. Successive extensions of the buildings had been made which barely kept pace with its growth in numbers. One of these extensions was the Hopkinson Wing, erected in memory of John Hopkinson and his son John by the surviving members of the family. There was a peculiar appropriateness in Bertram's appointment to be head of an establishment in whose creation his father had from the first taken a helpful interest, and whose development was in this way associated with his father's name. Under Bertram's leader- ship the prosperity of the Engineering School was more than maintained. It continued to grow in numbers and in academic and professional repute. Its attractiveness to students was in some sense a danger, but he was careful to fence the approach to the Tripos so effectively as to maintain a high standard. His own passion for research found in Cambridge a wider scope than had been open to it in the earlier part of his career. He entered there upon a period of remarkable productivity, stimulating selected students to attempt original work, and securing their co-operation in many important researches. He became a Fellow of the Royal Society in 1910, and was serving on the Council at the time of his death. His marriage, in 1903, almost coincided with the beginning of his pro- fessoriate. His wife, who was the eldest daughter of Mr. Alexander Siemens, survives him with seven daughters. In domestic life he found continuous quiet happiness, as well as freedom to pursue his scientific interests. There was no son who might have had from Bertram the same kind of nursing in scientific method that Bertram had from John. But if he had no son he had among his students not a few disciples who were fired by his teaching and example and were full of affection for their chief. Some of them will carry on the work he left undone. Others gave their lives, as he did, in the war. Of that band was his own brother Cecil, a man of rare promise, who passed out with First Class Honours in the Mechanical Sciences Tripos only a year before the war began. He had been his brother's assistant in more than one research. Cecil Hopkinson hastened to join the army in August, 1914, and received a fatal wound in Flanders near the end of the following year. Those who knew Cecil and his great potentialities felt the eclipse of that young life to be far more than a personal loss. To Bertram it was a grievous blow; but he did not let it disturb his absorption in war work, which by that time was complete. During his tenure of the Cambridge professorship, Hopkinson took no large part in the administrative work of the University outside of hisb own department, the claims of which were sufficiently exacting. He was, however, an energetic promoter of the Officers' Training Corps, and organised in it an engineering section, thereby maintaining a family tradition; for his father had been a pioneer in the foundation of the Corps of Electrical Engineers. In 1914 he accepted a professorial fellowship offered him by King's College. Outside the University he took a leading part in the work of more than one Research Committee. He served jointly with Sir Dugald Clerk as Secre- tary of the British Association Committee on Gaseous Explosions, whose Reports, spread over several years, contain records of many of his own experiments. He was an original member of the Advisory Committee set up in connection with the establishment of the Department of Scientific and Industrial Research. When the Royal Society appointed a committee of engineering experts to advise on problems of the war, Hopkinson became its secretary. The indirect effect of this was specially important; it brought him into close relations with the technical experts of the Army and Navy, and so did much to determine the direction which his energies took in the final years when his undivided efforts were given to national service. On the outbreak of the war he dropped all other interests. Obtaining a commission in the Royal Engineers he first undertook teaching duty at Chatham to relieve others for active service. Later he was engaged at the Admiralty in a department organised by the present writer, on work of a kind entirely new to him, which he took up with conspicuously good effect. It was mainly concerned with the collection of intelligence; but independently of that, he was at the same time occupied in conducting experi- ments in connection with an arrangement for the protection of warships from the effects of mines and torpedoes, by the addition to the hull of a "blister" or outer shell. His work showed, by experiments of gradually increasing scale, which were most ably carried out, that the law of comparison held good, subject to a certain modification in going to full size, and he suggested the insertion in the " blister" of a structure capable of absorbing the energy of an explosion in the act of becoming deformed, in lieu of a water-jacket. The value of his contribution was quickly recognised by the Admiralty; it at once received official acceptance and substantial acknow- ledgment. It has been applied in the design of some of the newest units of the Fleet, and is a feature of one of the most powerful of them, the battle cruiser " Hood." The origin of the suggestion is of interest, for it arose out of an earlier scientific research which Hopkinson had carried out with no idea at the time of putting it to this important use. For years before the war he had made a special study of explosions, their nature and the measure- ment of their effects. The events of 1914 gave this kind of knowledge a new significance. He applied himself to problems of attack as well as of defence, taking up not only the protection of ships, but the design of bombs for use by air-craft. From that he passed to the equipment of air-craft generally. He accepted a position under the Air Board, and in each succes- sive transformation of that branch of the Service the authority and responsi- bility of his office seemed to be enlarged. Some months before his death he had become a colonel and was awarded the C.M.G. Much of his work was done at an experimental station on the East Coast, but he had to visit many aerodromes, and he found that flying was his best means of locomotion. It was, moreover, an art he had to acquire in the interests of the work itself. He soon learnt to be his own pilot, and generally flew alone. It was in one of these flights that he fell, near London, in bad weather on August 26, and was instantly killed. The Air Council took the unusual step of recording " their deep sense of the high and permanent value of the work done for the Flying Forces by the late Colonel Hopkinson, and their recognition of the private self-abnegation with which he devoted his great abilities and scientific attainments to the public service "; and they communicated to the Vice-Chancellor of the University " an expression of profound regret at his untimely death and at the loss which has thereby fallen on the University of Cambridge." Of Hopkinson's work for the Air Force, the following notes have been furnished by one who served under him in it, Lieut.-Col. H. T. Tizard:- "His work in connection with flying began about March, 1915, when he was asked by the Department of Military Aeronautics to conduct experi- ments on bombs. These were carried out at Cambridge and elsewhere, and included the building of a model factory on a one-sixth linear scale on which the effect of model bombs was tested with the object of determining (a) the best proportion of bomb-case to weight of explosive, and (b) the best material of which to make the case. The experiments were continued until the end of May, 1915, when the model building was completed and the trials were witnessed by the Ordnance Board and representatives of other Govern- ment departments. While preparations for these trials were proceeding, he was consulted by the Superintendent of the iloyal Aircraft Establishment in connection with the design of bomb-sights. In July, 1915, he was appointed on the panel of Lord Fisher's Board of Invention and Research, and during the following months until November, his time was chiefly occupied in work for that Board, and in other experiments in connection with bombs and gyro bomb-sights both and at Cambridge and at Farnborough. " In November an official connection with the Royal Flying Corps was established by his appointment to the Department of Military Aeronautics, where he took charge of both the design and supply of bombs, bomb gears, guns, and ammunition. Most of the experimental work for the corps was at this time carried out either at manufacturers' works or at the Central Flying School, Upavon, and at Farnborough and Hythe. It was not long before Prof. Hopkinson saw the drawbacks of combining experimental and training work at one station, and he urged the formation of a separate station for the former. This recommendation was adopted, and an armament experimental station was started at Orfordness in the spring of 1916. The work of this station was entirely under the control of Prof. Hopkinson, and he threw his whole energies into its development. Most of the personnel was selected by him from existing R.F.C. stations. By the middle of 1916, in spite of the difficulties of working in temporary buildings, the station was in full swing. Shortly afterwards a large amount of the supply which had hitherto been done by Prof. Hopkinson's section at head- quarters, was transferred to a special supply section, which left him more time to devote to purely experimental work. The work at Orfordness had great influence on the development. of armament in the R.F.C. and subse- quently in the Air Force, and was very varied in character. It included the development of bombs, bomb-sights and methods of bombing; guns, gun-sights, and ammunition; self-sealing tanks and other accessories; and not least the systematic development of night flying, and of navigation in clouds and in bad weather, the influence of which work was beginning to be felt strongly at the time of his death, and will increase as time goes on. In all this work Major Hopkinson was at his best. He possessed the great capacity of understanding human limitations and knowing where, for war purposes, it was uneconomical to proceed further with the development of any particular scientific work. His judgment was well shown in the great pains he took to keep training and experiment in the closest possible contact. " The success of the work at Orfordness was such that it was soon decided to put the testing of aeroplanes, which up to this time had been done at the Central Flying School, also under his direction. Towards the end of 1916 this work was removed to Martlesham Heath. Major Hopkinson selected the site and made all preliminary preparations for clearing it and putting buildings in hand. The station soon developed in importance, and the work, which consisted of the testing of complete aeroplanes, of engines and other accessories as well as a certain amount of experimental photography, expanded considerably under his direction. " At the end of 1917 Lord Rothermere's reorganisation of the Air Force still further increased the scope of Major Hopkinson's duties. The experi- mental work at"the R.A.E. and the Naval Aircraft Experimental Stations at Grain, came under his control, and from this time until his death his influence on the general development of aeronautics steadily increased. He was appointed Deputy Controller of the Technical Department in June, 1918. "He found time, in spite of the pressure of his work, to learn to fly at Orfordness. There can be no doubt of the wisdom of this step, although many of his friends thought that it was an unnecessary risk. It increased both his judgment and his influence, especially his influence over the officers at the experimental stations. He took an intense pleasure in flying. He learned remarkably quickly for a man of his age, and was soon at home on many types of machines. At the time of his death he was flying a Bristol Fighter, and had started from Martlesham Heath on his way to London. The weather was threatening at the start, although the sky was only partly clouded, but in the neighbourhood of London the conditions were much worse and the sky was completely covered with low clouds. It seems clear that he flew above the clouds for some way, and then finding no gap descended through them. He probably lost control of the machine in the clouds (which would be quite easy for even a very experienced pilot to do on the type of machine he was flying), and on going through the clouds did not have sufficient time to regain control before the machine crashed, and he was instantaneously killed." It may be added that immediately before his death plans were being matured for the establishment of a great national school of Aeronautical Engineering, of which Hopkinson was to have been the head. Hopkinson's published work included a memoir of his father, written as a preface to the reprint of John Hopkinson's collected papers, as well as many accounts of his own researches. No attempt need be made here to analyse these, but a rough notion may be conveyed of the scope of the more important of them. For this purpose they may be grouped under three or four general heads. Two papers, written in conjunction with Sir Robert Hadfield, describe researches on the magnetic properties of alloys. The molecular theory of magnetism which ascribes the process of magnetisation to the turning into alignment of molecular magnets whose moment is constant, implies that there is a finite " saturation " limit to the magnetisation that can be reached under the influence of any magnetising, however great. According to the present writer's molecular theory, this limit is easily reached, for the mole- cular magnets are free to turn save for the control they exert on one another through their mutual magnetic forces. Experiments made as early as 1887 by the " isthmus " method had shown that this is the case in iron, and had determined the saturation limit. Hopkinson, adopting the "isthmus" method, confirmed this conclusion, and went on to examine the limit in a series of iron alloys prepared by Hadfield. These were steels containing various percentages of carbon, and the results confirmed Hopkinson's antici- pation that the magnetism of saturation might be predicted from the composition, treating each steel as a mixture of iron and of non-magnetisable carbide of iron. This deduction should follow from the principle (deduced from the molecular theory) that the saturation magnetism of an alloy is the sum of that of the constituents, when due account is taken of the propor- tions in which they are present, provided they behave simply as a mixture and do not interfere with one another's magnetic properties. It was found that this principle held good in carbon steels with sufficient exactness to suggest that measurements of magnetism might be used as a means of deter- mining the proportion of carbon present in the form of carbide of iron. It was similarly found that silicon and aluminium act mainly (in the magnetic sense) as inactive diluents. With manganese no such simple relation was discovered, and the anomalies which that metal presents in association with iron are suggestive in connection with the Heussler alloys, where it acts as one of three constituents, each non-magnetic when tested alone, to produce an alloy that has a strongly marked magnetic quality. Another joint paper, published by the Iron and Steel Institute in 1914, describes an interesting investigation of the very complicated magnetic properties of Hadfield's manganese steel, which can be toughened by sudden cooling from a high temperature, in which state it is non-magnetic, but can be made to assume various degrees of magnetic susceptibility by prolonged exposure to moderate heat. Another group of papers deals with the elastic properties of steel and other metals and the departure from perfect elasticity which is known as elastic hysteresis (' Roy. Soc. Proc.,' A, vols. 76, 86, and 87). In the course of the investigation Hopkinson devised a high-speed fatigue-tester for examining the endurance of metals under alternating stresses of great frequency. With this machine he could reverse the stress in the specimen with perfect regu- larity as often as 7000 times per minute, measure the amount of energy dissipated internally through elastic hysteresis, and determine the number of repetitions that were required to produce fracture for various ranges of stress, as well as the range that could (apparently) be endured without fracture, no matter how often the reversal of stress might be repeated. Apart from the interest of the results, the methods of observation described in these papers have much individuality, and may be expected to open the way to further discovery in the same field. The development of the gas engine and other internal combustion motors appealed strongly to Hopkinson as a practical matter on which scientific consideration could usefully be brought to bear. He invented a method of internal cooling, of which great things were hoped, but the results were disappointing. He also invented an optical indicator, which proved itself to be a most effective instrument for revealing what happens in the cylinder. He investigated problems of heat flow and temperature distribution, and he gave much time to the study of gaseous explosions by means of experiments in which a mixture of gas and air was ignited in a closed vessel furnished with appliances for exhibiting and recording the action at various points in the interior, from which the true nature of the action and the manner in which the explosion was communicated from point to point could be inferred. The devices used in this research were of great ingenuity, and the experiments were prosecuted with conspicuous thoroughness. They cleared up matters that had been obscure, and removed a number of current misconceptions. Sir Dugald Clerk has been good enough to furnish the following notes regarding Hopkinson's labours in this field:- "The science of flame and explosion has suffered a great loss by the death of Bertram Hopkinson. He was one of the most brilliant and enthusiastic experimenters in that field, and carried out very important investigations into the phenomena of gaseous explosion by which he arrived at valuable and interesting conclusions. He demonstrated that in gaseous explosions the maximum temperature is attained in the space surrounding the ignition point. This is due to the adiabatic compression of the flame first formed at the sparking position, by the compression due to the rise in pressure produced by the inflammation of the outer layers, and the temperature there may be raised as much as 300? C. above the average of the explosion from that cause alone. " He also proved by the use of platinum wire resistance thermometers that in such explosions within closed vessels, the expanding flame fills the whole vessel considerably before the termination of the rise in pressure. This had been inferred in early explosion experiments by other experimenters, but the inference depended on a study of the changes occurring in the rate of rise of the explosion curve; it remained for Hopkinson to prove definitely by resistance thermometer observations that the flame reached the sides of the vessel in advance of the point of'maximum explosion pressure. " Hopkinson also determined the effect of radiation from the flame in checking the rise of pressure and in altering the rate of cooling. His first experiments were made with cylindrical vessels silver-plated internally and highly polished. In these vessels the maximum pressure increased about 4 lbs. per square inch, equivalent to a temperature rise of 70? C., in the polished vessels as compared with experiments with the same mixtures in the same vessels with the polished surface blackened over. "To study further the radiation from high temperature explosion, Hopkinson designed an ingenious apparatus by which the flame radiation passed through a fluorite window in the explosion vessel, and was measured by means of a platinum strip bolometer. By this he determined that the loss of heat during the explosion period of 0'05 second amounted to nearly 5 per cent. of the whole heat of combustion. Hopkinson continued this investigation with his pupil David, and added greatly to our knowledge of the behaviour of flame as to loss by radiation at about 2000? C. His experiments also on the residual turbulence within the cylinder of internal combustion engines assisted materially in clearing up our ideas on the effect of the inlet velocity of the gaseous charge upon the economy and action of working engines. "Colonel Hopkinson was most able and resourceful in all his experimental work, which threw much light on the phenomena of gas and petrol engines. He applied his great knowledge to the service of the Admiralty and the War Office while he was Secretary of the Engineering War Committee of the Royal Society, and later in his official position as Deputy Controller of the Technical Department in charge of aeroplane and aero-engine design and construction. His loss is keenly felt by his scientific colleagues and his associates of the Army and Navy." In still another group of researches Hopkinson dealt with the dynamics of explosions from a different point of view. His paper on ' A Mlethod of Measuring the Pressure produced in the Detonation of High Explosives, or by the Impact of Bullets," read before the Royal Society in November, 1913, and published in the 'Philosophical Transactions,' describes an investigation remarkable for its completeness no less than its originality. Taking the familiar method of the ballistic pendulum, which serves to measure the momentum of a blow, Hopkinson shows how to analyse this into its two factors, force and time, by means of a novel and ingenious variant. He used for the pendulum a steel rod divided by a transverse joint into a long and a short portion. The rod takes the blow longitudinally and transmits it as a wave of elastic compression which proceeds from the long piece to the short one. At the extreme end of the short piece the wave of com- pression is reflected back along the rod as a wave of tension, and when the reflected wave reaches the joint the short piece flies off, carrying with it a fraction of the whole momentum which depends upon its length. By adjusting the length of the short piece it may be made to absorb the whole of the momentum of the blow, leaving the main portion of the rod at rest. This enables the length of the pressure wave to be determined, and from that the duration of the blow is readily inferred. Moreover, by using a very short length for the detachable piece the maximum pressure is also measured. The detachable piece is at first maintained in contact with the main portion of the rod by magnetic attraction, which keeps them together while the compression wave passes, but allows them to separate easily as soon as the stress at the joint changes into tension. Applying this method to examine the blow given by a leaden bullet when fired so as to strike normally the end of the rod in the direction of the length, Hopkinson found that the results confirmed the view that the bullet behaved on impact like a fluid, producing at high speeds nearly the same pressure as could be produced by a fluid jet of corresponding velocity, density, and form. The duration of the blow was only slightly greater than that of such a jet. He discusses fully the causes of the small discrepancy, which is due in part to rigidity in the bullet and in part to the fact that the strain transmitted along the rod is not a simple wave of compression, uniform over the whole cross-section. But the discrepancy is so snfall as not to interfere with the value of the method as a means of measuring the force and duration of any blow. From the blows of bullets he passed to those caused by the detona- tion of gun-cotton near or close to one end of the rod, determined approxi- mate limits of maximum pressure, and showed that at least 80 per cent. of the impulse of the blow had been delivered in one fifty-thousandth part of a second. The results detailed in the paper throw much light on the process of detonation and on the manner in which it produces its destructive effects. Notably here, and scarcely less in some of his other papers, Hopkinson's scientific writing recalls that of his father. In saying this, one pays it a high tribute. There is the same absence of excrescence and verbiage and vagueness, the same avoidance of side issues, the same direct approach to the very core of the subject; there is the same impression of mastery and ease. Perhaps it is too terse; certainly it is so terse as to need very careful reading. But the careful reader is satisfied as well as convinced. What was said in this place* twenty years ago of the father's writings is no less true of the son's. His writings, indeed, reflect the sincerity of the man. It was apparent to all with whom he came in contact; he quickly won their liking and respect. His nature was strong and self-reliant, singularly free from. egotism or self-seeking. An obviously forceful personality, impressive in figure, in manner, in voice, he was conscious of his power, though not in. the least vain of it. No doubt this contributed to another notable characteristic, that his good-humour was imperturbable. His temper kept sunny under the most trying conditions. Always a cheerful comrade, willing to take a full share of any duty, to respond to any demand, buoyant, frank, open, careless of self, he was a delightful associate in office or committee-room. One felt he lacked something, especially in his earlier years, of that conm- prehension of other men's idiosyncracies and weaknesses which is essential to perfect sympathy; but as time went on his experience, first as a teacher and later as an administrator, mellowed him. Among the men with whom he worked he was, it seemed, a universal favourite. On the scientific side Hopkinson's strength lay, just as his father's did, in his combining a comprehensive grasp of principles with a just appreciation of practical requirements and possibilities. It was this combination that made him a successful head of the Engineering School at Cambridge, and determined the character of his researches; it was this again that made the value of his war work almost unique. The experiments of the Cambridge laboratory were of high interest in themselves and in their bearing on engineering practice. But to Hopkinson they were more; one may say they constituted an apprenticeship for the culminating work of his life, the work of the last four years, The war gave him an opportunity such as he did not have before. Into it he threw all his inventiveness, all his initiative, his untiring energy, his power of organisation, his unrivalled capacity for getting the best out of himself and out of others. No worker rejoiced more in his work nor accepted its call with more absolute self-renunciation. He was amazingly aloof from any consideration of private advantage or personal convenience. The strain was immense: the pressure of claims on his attention was continuous, but it never seemed to ruffle his serenity nor impair the soundness of his judgment. Many will mourn him as a trusted friend, but only those who knew something of what he did in the war can have a right idea of the magnitude of the nation's loss. The President of the Royal Society, speaking as Master of Trinity in a Commemorative Sermon at the College, said of him: " Our Roll of Honour contains the name of no one who has rendered greater services to his country."

J. A. E.

Major Bertram Hopkinson, C.M.G., F.R.S., was killed on August 26th in a flying accident near London. He had been Professor of Mechanism and Applied Mechanics at Cambridge since 1909, and was a Professorial Fellow of King's. He was the eldest and last surviving son of the late Dr. J. Hopkinson, F.R.S., the engineer and physicist, who was a nephew of the late Mr. J.B. Dewhurst, and cousin of Mr. Algernon Dewhurst J.P., of Aireville, Skipton. A brother of Major Bertram Hopkinson (Lieut. Cecil Hopkinson) died of wounds recently.

The death of Major Hopkinson recalls the tragic Alpine accident of twenty years ago, when. on August 27th, 1898, Dr. John Hopkinson, father of the deceased officer, with another son, Jack, and two daughters, Alice and Lina, were killed, and the new wing of the Engineering School at Cambridge University was erected to their memory. There is now only one daughter left of the family, namely Lady Ewing, wife of Prof. Ewing.

Major Bertram Hopkinson was born in January, 1874. He was educated at St. Paul's School and Trinity, Cambridge, where, owing to illness, he was forced to take an acgrotat degree in the Mathematical Tripos, Part I., 1895; but in 1896 he was placed in the first class, Division I., of the Second Part. He was called to the Bar in 1897. On his father's death, however, in the following year, in the Alpine accident already referred to, Major Hopkinson started in business as a consulting engineer in partnership with Mr. Charles Hopkinson and Mr. Ernest Talbot, and jointly with them he was responsible for the design of the electric tramways at Leeds and Newcastle-on-Tyne and many other public works. He was a member of the Institution of Civil Engineers was elected a Fellow of the Royal Society in 1910, and was created a C.M.G. in 1917. He edited Original Papers by his father, with a memoir, and was the author of several scientific and technical papers read before the Royal Society, the Institution of Civil Engineers, and other scientific bodies. He carried out a good deal of experimental work on the phenomena of explosion, measuring, for example, the duration of the pressures produced by the detonation of gun-cotton, and investigating the precise course of events which happen when a mixture of gas and air is burnt in conditions such as obtain in the cylinder of a gas-engine. In 1903 he married the eldest daughter of Mr. Alexander Siemens. The funeral will be a military one, and will take place at Cambridge today (Friday).