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Department of Physics

The Cavendish Laboratory

"Dennis Moralee"

"The systematic teaching of practical physics is a modern development. Until the second half of the nineteenth century was well begun, no teaching laboratory and no regular course of instruction were known."

So used are we nowadays to the large, carefully organised and elaborately equipped University teaching laboratory that this statement (with which the original History of the Cavendish begins) seems somewhat startling. But in fact it understates the case, for, until that period just over a century ago, no central facilities of any kind existed for the practice of experimentally based physics. The Physics Faculty, with its essential components - the laboratories and workshops, the lecture rooms and libraries, the stores and offices - is, like all the other faculties, quite a modern innovation. All the immense amount of scientific knowledge built up before the 1870's was the result of individual work in essentially private labs. The wealthy amateur physicist, such as Joule or Cavendish, would have a laboratory at his home, while the academic scientist would work in his college rooms. The tremendous contributions to science produced by, for example, Newton at Trinity, Young at Emmanuel, and Stokes at Pembroke were all accomplished in their own accommodation and largely by themselves. Any assistance they might have would be relatively unskilled - for instance Newton's poor eyesight led him to employ others to describe the results of his optical work to him. But, astonishingly, helping an acknowledged master of experimentation was the only way open to a student physicist to receive any teaching in experimental techniques whatsoever. Indeed such knowledge was actively discouraged by some academics, such as the great Cambridge mathematician Dr. Isaac Todhunter, who said: "Experimentation is unnecessary for the student. The student should be prepared to accept whatever the master told him."

Around the middle of the nineteenth century a great deal of discussion arose about the practical training of scientists and engineers at all levels. The British Association, the Great Exhibition, and the Science Museum all came out of this enthusiasm for spreading scientific knowledge. So too came our own Natural Sciences Tripos in 1851, but teaching for the new Tripos was, in physics at least, entirely theoretical, based on the ancient mixture of public lectures and private reading. The only university to have anything like an organised laboratory was Glasgow, where, in the 1840's, William Thompson, later Lord Kelvin, "took over an old wine cellar in his predecessor's house.... threw out the bins, installed a water supply and a sink, and called the room a physical laboratory." Many students were taught in this laboratory and some remarkable work produced, but still the student worked only as the Professor's assistant, not on any organised course, and only a few students could be accommodated in this way.

Twenty-five years later pressure for the establishment of organised practical teaching was irresistible. Oxford and Cambridge reacted in their own fashions to it. Oxford began building the Clarendon, and in Cambridge the Senate formed a committee to look into the question. When, in 1869, the committee reported, it was clearly in favour of creating a Cambridge Physics Laboratory, recommending the "founding of a special Professorship, and of supplying the Professor with the means of making his teaching practical - in other words, of giving him a demonstrator, a lecture-room, a laboratory, and several class-rooms, with a sufficient stock of apparatus." However, at this time the University's finances were not very healthy, and the report had to be shelved. How long things would have remained in this state is not known, but after 18 months, the then Chancellor wrote to the University offering to meet the estimated cost which was the frightening sum of £6,300. The Chancellor was the seventh Duke of Devonshire, himself a Smith's prize winner and Senior Wrangler, and a distant relative of Henry Cavendish. Indeed 'Cavendish' was the family name, and so, finally, the new laboratory became known as the Cavendish.

All this created, of course, a great deal of interest in Cambridge, particularly among the group of young mathematicians, mostly recent graduates, who were likely to be the first students at the new lab. It might at first seem surprising that the prospective students should nearly all be mathematicians, and in addition mostly graduates, but maths had, at that time, a very firm hold on Cambridge life. Introduced in 1747, the Mathematical Tripos eventually became the course for all serious students. Indeed, until 1850 no student could obtain an honours degree without first qualifying in the Maths Tripos, and those of a non-mathematical disposition either "ploughed it", like Macaulay, or entirely refused to graduate, like Gray. Mathematics was described as the vampire of the Cambridge schools, and had absorbed not only philosophy, but also the arts and natural sciences. The nineteenth century finally saw the breaking of this monopoly with the establishment of several Triposes for Classics (1822), Moral Sciences (1851), and, as we have seen, Natural Sciences, also in 1851. But the development of these Triposes was relatively slow, and even in 1874 the N.S.T. could boast only 19 students, compared with some 1500 a century later. The Mathematical Tripos itself, with its rigid order of merit, was an extremely competitive one and undergraduates in it could not fairly be expected to do practical work as well. So the first students at the projected Cavendish Laboratory were bound to be Mathematics graduates.

There was, naturally, much speculation about the choice of the new Professor of Experimental Physics. Kelvin was the most likely candidate, but on being approached in private, refused in order to stay in Glasgow. Another likely candidate was Lord Rayleigh, a brilliant mathematician and physicist who had left Cambridge to work in his private laboratory at his country seat in Essex. When the appointment was eventually announced, the reaction was, if anything, one of disappointment. The new Professor, James Clerk Maxwell, was relatively unknown. He had, it was true, been Senior Wrangler in 1854, joint Smith's prizeman and a much respected mathematician, but he had not since made any great name for himself - his major and astounding books on Electricity and Kinetic Theory had yet to be published. Moreover, the six years before his appointment had been spent in isolation at his Scottish home. Actually during this time he had, as an examiner for the Mathematical Tripos, done much to change the emphasis of the examination to more physical topics. His appointment was announced on March 8th 1871, and in spite of the initial disappointment, his inaugural lecture was looked forward to by his likely students as much as by the rest of the Cambridge scientists.

Maxwell's Cavendish

An inaugural lecture was then, even more than now, a special occasion to be attended by all the leading personalities of the University. However, Maxwell made only a casual announcement of his inaugural lecture which was not to be in the Senate House, as expected, but in an out-of-the-way lecture room. Consequently only his students got to hear of it and it was to them, rather than a general gathering, that he delivered an exciting and interesting lecture, mapping out his plans for the future of Cambridge physics. "The familiar apparatus of pen, ink and paper will no longer be sufficient for us, and we shall require more room than that afforded by a seat and desk, and a wider area than that of a blackboard", he said, emphasising the revolution in learning that the new laboratory was about to initiate. "We should begin, in the lecture room, with a course of lectures on some branch of physics, aided by experiments of illustration, and conclude, in the laboratory, with a course of experiments of research." This was perhaps the first positive statement that the new laboratory was to be a place of original research as well as of teaching.

When, a few days later, Maxwell began his first course with a lecture on Heat, his students had the delight of seeing the lecture room packed with their tutors, lecturers, professors and all the important personages of the University. Thinking that this was his first public appearance they sat, in their formal academic dress, while Maxwell, "with a perceptible twinkle in his eye", gravely expounded the difference between Fahrenheit and Centigrade, and the principle of the air thermometer.

It was felt afterwards that Maxwell had done it on purpose, perhaps out of modesty, perhaps out of his later well-known sense of humour, or perhaps because he knew of the still considerable opposition his new laboratory had to face. As he had written to his friend Lord Rayleigh, "if we succeed too well, and corrupt the minds of youth till they observe vibrations and deflections and become Senior Ops. instead of Wranglers, we may bring the whole University and all the parents about our ears."

In the three year period between his inauguration and the opening of the Cavendish, Maxwell was busy not only on planning and supervising the construction of the Laboratory, but also in giving his scheduled courses of lectures on Heat, and on Electricity and Magnetism. Before the Cavendish was ready he had to hop from one lecture room to another, depositing his notions, as he said, like a cuckoo depositing its eggs. Maxwell had a reputation for being a bad lecturer - it was rumoured that his earlier departure from King's College, London stemmed from this cause - but those attending his lectures seem to have been very impressed. Apart from the graduates who were hoping to start work in the new laboratory, among them (Sir) Horace Lamb, his lectures were attended by undergraduates who had to take the Heat, Electricity and Magnetism paper which had been re-introduced into the Mathematical Tripos that year (1872-73). Lamb leaves a record of his impressions of Maxwell's lectures. Although he, as a graduate, found their subject matter elementary, he was struck by the "illuminating glimpses we got of the lecturer's own way of looking at things, his constant recourse to fundamentals, and even his expedients when in difficulty, the humorous and unpremeditated digressions, the occasional satirical remarks, and often a literary or poetical allusion." Apparently he had his "full share of misfortunes with the blackboard and one gathered the impression, which is confirmed I (Lamb) think, by a study of his writings, that, though he had a firm grasp of essentials, and could formulate great mathematical conceptions, he was not very expert in the details of minute calculations. His physical instincts saved him from really vital errors."

In 1873 Maxwell's work on Electricity and Magnetism appeared in the Cambridge bookshops, where there was "a great rush for copies". The effect of this facet of Maxwell's work on the history of physics has been, of course, enormous, but in Cambridge in particular it formed the starting point for a long series of theoretical and experimental investigations. Its publication must have dispelled any lingering doubts as to Maxwell's scientific abilities.

Meanwhile work had continued on the Cavendish Laboratory. Maxwell had put into the planning of the building an amazing amount of detailed work, making it the first specially designed physics laboratory in the world. Probably the best contemporary description of the laboratory appeared in Nature, (then a young publication), reprinted with this article. The actual final cost of the building was £8,450, but the Duke paid up without a murmur and indeed went further to equip the laboratory at his own expense. The lecture room (now appropriately called the "Maxwell") and the students' laboratory came into use in the Michaelmas Term of 1873, but the opening ceremony did not take place until June 16th 1874.

As soon as the new laboratory was open, research work was begun by the small band of graduates who were waiting to begin practical studies. "A goodly company of Dons", they have been called, and indeed it must be remembered that they all were Dons in the well understood if difficult to define sense of the word - all Fellows of colleges, and many, like Lamb, junior lecturers. The research degree was not incorporated into the Cambridge system for another twenty years, and when it was it did, of course, greatly change the face of the University. However, long before the foundation of the Ph.D. course, graduates of other universities wanted to come and join in the research work. When they did, they could have no official status, for officially they did not exist. At least one of them, (Sir) Arthur Schuster, later professor at Manchester, managed to be appointed a fellow commoner at St. John's - only, however, after a very long argument over which gown he should wear. It was finally settled by the Master himself who allowed him the indulgence of wearing a B.A. gown, but emphasised Schuster's unworthiness by first carefully cutting the strings off.

Maxwell's idea was that each graduate should go straight into a piece of research after a short course of training in measurement. It is hard for us, who since the age of eleven or so have had practical training in measurements of one sort or another, to realise that these men, all of them highly successful Mathematics fellows, would have little or no experience in scientific measurement. Various experiments were designed by Maxwell to train them in these, to us automatic, techniques, but his favourite one was the "Kew" Magnetometer, a large device abundantly covered in scales, things requiring delicate adjustment, and with a swinging magnet to time. Everyone was 'invited' to measure the earth's field with this device, which played an extremely long-lived role in Cambridge Physics, being still in use half a century later.

The very first student was W.M. Hicks, later professor at Sheffield. After his battles with the Kew Magnetometer he constructed an electrometer from a newly published design. Then, embarking on what was presumably the first research project done in the Cavendish, he attempted to measure the velocity of the electromagnetic waves which had been predicted in Maxwell's book of the previous year. He designed the apparatus which depended on "the action of two coils, a large one and a very small one, on the same circuit, acting on a light magnetic needle at a point where their combined force was zero. As the large coil was much further away, I supposed that when the current was suddenly started, or suddenly stopped, the effect of one on the needle would disappear before the other, and the needle would give a kick. Of course nothing came of it." Now this is very reminiscent of the people of the early Eighteenth Century trying to measure the speed of light by flashing lanterns at each other from hilltops. Since Maxwell had in his book proved the equivalence (or, because of the inaccuracy of the then available data, very near equivalence) of the velocity of 'his' waves and that of light, it should have been obvious that any such experiment on a laboratory scale would not work. Perhaps this was the very first example of a general rule Maxwell later explained to Schuster, "I never try to dissuade a man from trying an experiment; if he does not find out what he is looking for he may find something else."

One of Maxwell's first acts as professor was to appoint a demonstrator for the laboratory. This was William Garnett, who had impressed Maxwell in his Tripos answers the previous year, when he was Fourth Wrangler. He held the position until Maxwell's death. One of his major innovations was the Cavendish workshop which has steadily expanded and can, with complete accuracy, be said to be the starting-point of both the University Engineering Laboratory (who took over all the more important work) and of the well known Cambridge firm of Pye, W.G. Pye, its founder, having been in charge of the workshop later in its existence.

Soon undergraduates began to use the laboratory in increasing numbers, and three years after the opening, elementary lectures in practical topics were begun by Garnett. There was not, however, an organised practical course, but students followed their own needs and ideas. This system may have been admirable from some points of view, but Schuster says "the advantage was not always appreciated by the student, who was nervously apprehensive of the coming examinations." For the days of the practical examination had arrived. In the first paper students were "given an opportunity to show that they could find the focal length of a lens, the time of vibration of a magnet, or the electrical resistance of a wire." What students made of this paper is not known, but the results of a paper set some years later are, and they deserve to be famous. The examination was in the form of a viva, with the student, who had taken the same elementary course as the N.S.T. men but who was in fact trying for the 1st M.B., being asked to identify a piece of apparatus and then make a measurement with it. Firstly there was "the man who said that a compass needle mounted on a graduated circle was an instrument for determining the latitude and longitude." He was eventually followed by "the man who recognised in a thermometer a machine for determining the specific gravity of water." The examiner was cruel enough to go and fetch a bowl of water and a bit of string, to help him in the task. It is not known how long he kept him in his suffering until he finally dismissed him and noted that "he failed to achieve any numerical result".

One notable characteristic of the Cavendish under Maxwell's leadership was the absence of women students, whom Maxwell would not allow into the laboratory. Finally he allowed women to use the laboratory, but only during the long vacation, when he himself was safely in Scotland. One group of women physicists, always more earnest in studies than their male counterparts, rushed through a whole year's course in a few weeks. Only in 1882 did Rayleigh end sexual discrimination in the Cavendish.

Maxwell's health began to fail after only a few years at the Cavendish. He still made his rounds of the Laboratory, however, and still lectured. After his first year, though, attendances had fallen, and in 1879 (Sir) Ambrose Fleming was to note that only he and "an American gentleman from St. John's" went to lectures. Fleming was astonished, for he considered that in any Scottish or German university, Maxwell would have crowded out the lecture theatres, but in Cambridge lectures were never as a rule well attended. But in spite of carrying on lecturing for just the two of them until the very end of the year, his health deteriorated. He died in November of 1879.

It would be difficult to pick out Maxwell's greatest achievement in the Cavendish. Firstly his planning and ideas for its operation were essential to its success. Secondly he was behind all the very important research projects started in his day. Perhaps one could choose just one chain of experimentation he started. Although it was Hertz in Germany who first did what Hicks had tried to do and demonstrated the existence of "Maxwell's" e.m. waves, work was carried on in the Cavendish for many years. Sir Oliver Lodge performed much research which finally bore fruit in practical use, but most remarkable of all was Rutherford's work in the mid-1890's. He gradually succeeded in establishing wireless communication over first a hundred yards, then half a mile, finally as far as the Observatory. He reckoned that if he could attain a range of ten miles he could make a fortune out of it. However he was told that the commercial prospects were negligible, and Kelvin could not get the £100,000 he thought he would need to develop the idea. Consequently Rutherford decided to try his hand at what is now known as Atomic Physics. But, admittedly through a broken chain, radio propagation and reception stayed as a Cambridge project, and perhaps it's not being too fanciful to trace a connection between Hicks' original experiment and the aerials over at Lord's Bridge.

Rayleigh's Term of Office

The regulations for the Cavendish chair clearly said it was to terminate at Maxwell's death unless the Senate decided otherwise. The Senate must have been convinced of the value of the Cavendish, for it immediately offered the chair to Lord Rayleigh, who was universally agreed to be the only successor to Maxwell.

Of the eight Cavendish Professors who have so far headed Cambridge physics, Rayleigh is perhaps the least known, and his period of occupancy of the chair is certainly the most difficult to write about. Firstly because his researches, although covering a wide field, were completely classical, and one tends to jump straight from the Maxwell era to the atomic physics of J.J. Thomson's tenancy. Secondly because his most important work in Cambridge was concerned with the re-determination of the absolute values of various electrical quantities, notably the ohm. Such work is always vital, and was particularly so then, but definitely not as glamorous as original research. Thirdly, all the major discoveries of Rayleigh's, particularly those for which he is famous (for example, the noble gases), were made at his private laboratory at Terling, to which he returned after his time at the Cavendish.

Perhaps Rayleigh would not have accepted the chair at all had there not been an agricultural depression at the time. Rayleigh's estate depended on his dairy herds, and in particular on the chain of dairy shops and milk-rounds that he operated in London, cutting out the middleman. "Lord Rayleigh's Dairies" were a well known and profitable business, but it so happened that in 1879 profits were falling. Consequently Cambridge gained one of the greatest classical physicists.

On arriving at the Cavendish, Rayleigh discovered that the lab was severely under-equipped. In spite of Maxwell having continuously added apparatus of his own, the growth in the number of students had left a real shortage. Rayleigh modestly asked for a fund of £1,500. The Duke gave £500, Rayleigh himself contributed £500, and the rest was soon raised. It was generally thought odd that more equipment was necessary, for Maxwell in a report of 1877 had stated that "the Chancellor has completed his gift of apparatus." Somehow this was changed by word of mouth into the statement that the Chancellor had completely equipped the Cavendish. In fact the Chancellor's gift was quite insufficient. The type of equipment used at the Cavendish in those early days can be seen from the part of Maxwell's report reprinted (page 19).

In addition to the gift of new equipment, Rayleigh also expanded the workshops, but his most important step was the setting up of an organised practical course. Garnett left after Maxwell's death, and in his place were appointed jointly (Sir) R.T. Glazebrook and W.N. Shaw. Together they perfected the new type of practical teaching that is now standard - a series of set experiments are laid out and allotted in rota to the students. Handouts are available and the demonstrator wanders round solving any problems that arise. Trivial as this step forward may seem, it completely revolutionised practical instruction. Rayleigh himself did a lot of preparatory work, and Glazebrook and Shaw's book on Practical Physics became the standard (and only) practical textbook for many years.

The division of the N.S.T. into two parts had enabled advanced as well as elementary classes to be operated. The complete lecture list for 1880 is reproduced below. The practical classes were for two hours, three days per week. Attendances were still fairly small - 16 at Rayleigh's lectures, 18 doing Heat, 14 doing Advanced Electricity. However the numbers soon grew and some demonstrations had to be duplicated.

The organisation of this expanded laboratory was a major task and Rayleigh was responsible for a great deal of it. Still, in his five years at the Cavendish, he managed to publish fifty papers - a Nobel Prize was founded in 1904 on this tremendous body of work. It was the first such recognition of the scientific work of the Cavendish, and forms a fitting conclusion for a review of the first decade of Cambridge physics.