Читать книгу James Clerk Maxwell and Modern Physics - Richard Glazebrook - Страница 8

Table of Contents

From this time on Maxwell’s life becomes a record of his writings and discoveries. It will, however, probably be clearest to separate as far as possible biographical details from a detailed account of his scientific work, leaving this for consecutive treatment in later chapters, and only alluding to it so far as may prove necessary to explain references in his letters.

He continued in Cambridge till the Long Vacation of 1854, reading Mill’s “Logic.” “I am experiencing the effects of Mill,” he writes, March 25th, 1854, “but I take him slowly. I do not think him the last of his kind. I think more is wanted to bring the connexion of sensation with science to light, and to show what it is not.” He also read Berkeley on “The Theory of Vision” and “greatly admired it.”

About the same time he devised an ophthalmoscope.19

“I have made an instrument for seeing into the eye through the pupil. The difficulty is to throw the light in at that small hole and look in at the same time; but that difficulty is overcome, and I can see a large part of the back of the eye quite distinctly with the image of the candle on it. People find no inconvenience in being examined, and I have got dogs to sit quite still and keep their eyes steady. Dogs’ eyes are very beautiful behind—a copper-coloured ground, with glorious bright patches and networks of blue, yellow, and green, with blood-vessels great and small.”

After the vacation he returned to Cambridge, and the letters refer to the colour-top. Thus to Miss Cay, November 24th, 1854, p. 208:—

“I have been very busy of late with various things, and am just beginning to make papers for the examination at Cheltenham, which I have to conduct about the 11th of December. I have also to make papers to polish off my pups. with. I have been spinning colours a great deal, and have got most accurate results, proving that ordinary people’s eyes are all made alike, though some are better than others, and that other people see two colours instead of three; but all those who do so agree amongst themselves. I have made a triangle of colours by which you may make out everything.

“If you can find out any people in Edinburgh who do not see colours (I know the Dicksons don’t), pray drop a hint that I would like to see them. I have put one here up to a dodge by which he distinguishes colours without fail. I have also constructed a pair of squinting spectacles, and am beginning operations on a squinting man.”

A paper written for his own use originally some time in 1854, but communicated as a parting gift to his friend Farrar, who was about to become a master at Marlborough, gives us some insight into his view of life at the age of twenty-three.

“He that would enjoy life and act with freedom must have the work of the day continually before his eyes. Not yesterday’s work, lest he fall into despair; nor to-morrow’s, lest he become a visionary—not that which ends with the day, which is a worldly work; nor yet that only which remains to eternity, for by it he cannot shape his actions.

“Happy is the man who can recognise in the work of to-day a connected portion of the work of life and an embodiment of the work of Eternity. The foundations of his confidence are unchangeable, for he has been made a partaker of Infinity. He strenuously works out his daily enterprises because the present is given him for a possession.

“Thus ought Man to be an impersonation of the divine process of nature, and to show forth the union of the infinite with the finite, not slighting his temporal existence, remembering that in it only is individual action possible; nor yet shutting out from his view that which is eternal, knowing that Time is a mystery which man cannot endure to contemplate until eternal Truth enlighten it.”

His father was unwell in the Christmas vacation of that year, and he could not return to Cambridge at the beginning of the Lent term. “My steps,” he writes20 to C.J. Munro from Edinburgh, February 19th, 1855, “will be no more by the reedy and crooked till Easter term.... I should like to know how many kept bacalaurean weeks go to each of these terms, and when they begin and end. Overhaul the Calendar, and when found make note of.”

He was back in Cambridge for the May term, working at the motion of fluids and at his colour-top. A paper on “Experiments on Colour as Perceived by the Eye” was communicated to the Royal Society of Edinburgh on March 19th, 1855. The experiments were shown to the Cambridge Philosophical Society in May following, and the results are thus described in two letters21 to his father, Saturday, May 5th, 1855:

“The Royal Society have been very considerate in sending me my paper on ‘Colours’ just when I wanted it for the Philosophical here. I am to let them see the tricks on Monday evening, and I have been there preparing their experiments in the gaslight. There is to be a meeting in my rooms to-night to discuss Adam Smith’s ‘Theory of Moral Sentiments,’ so I must clear up my litter presently. I am working away at electricity again, and have been working my way into the views of heavy German writers. It takes a long time to reduce to order all the notions one gets from these men, but I hope to see my way through the subject and arrive at something intelligible in the way of a theory....

“The colour trick came off on Monday, 7th. I had the proof-sheets of my paper, and was going to read; but I changed my mind and talked instead, which was more to the purpose. There were sundry men who thought that blue and yellow make green, so I had to undeceive them. I have got Hay’s book of colours out of the Univ. Library, and am working through the specimens, matching them with the top. I have a new trick of stretching the string horizontally above the top, so as to touch the upper part of the axis. The motion of the axis sets the string a-vibrating in the same time with the revolutions of the top, and the colours are seen in the haze produced by the vibration. Thomson has been spinning the top, and he finds my diagram of colours agrees with his experiments, but he doubts about browns, what is their composition. I have got colcothar brown, and can make white with it, and blue and green; also, by mixing red with a little blue and green and a great deal of black, I can match colcothar exactly.

“I have been perfecting my instrument for looking into the eye. Ware has a little beast like old Ask, which sits quite steady and seems to like being looked at, and I have got several men who have large pupils and do not wish to let me look in. I have seen the image of the candle distinctly in all the eyes I have tried, and the veins of the retina were visible in some; but the dogs’ eyes showed all the ramifications of veins, with glorious blue and green network, so that you might copy down everything. I have shown lots of men the image in my own eye by shutting off the light till the pupil dilated and then letting it on.

“I am reading Electricity and working at Fluid Motion, and have got out the condition of a fluid being able to flow the same way for a length of time and not wriggle about.”

The British Association met at Glasgow in September, 1855, and Maxwell was present, and showed his colour-top at Professor Ramsay’s house to some of those interested. Letters22 to his father about this time describe some of the events of the meeting and his own plans for the term.

“We had a paper from Brewster on ‘The theory of three colours in the spectrum,’ in which he treated Whewell with philosophic pity, commending him to the care of Prof. Wartman of Geneva, who was considered the greatest authority in cases of his kind—cases, in fact, of colour-blindness. Whewell was in the room, but went out and avoided the quarrel; and Stokes made a few remarks, stating the case not only clearly but courteously. However, Brewster did not seem to see that Stokes admitted his experiments to be correct, and the newspapers represented Stokes as calling in question the accuracy of the experiments.

“I am getting my electrical mathematics into shape, and I see through some parts which were rather hazy before; but I do not find very much time for it at present, because I am reading about heat and fluids, so as not to tell lies in my lectures. I got a note from the Society of Arts about the platometer, awarding thanks and offering to defray the expenses to the extent of £10, on the machine being produced in working order. When I have arranged it in my head, I intend to write to James Bryson about it.

“I got a long letter from Thomson about colours and electricity. He is beginning to believe in my theory about all colours being capable of reference to three standard ones, and he is very glad that I should poach on his electrical preserves.

“... It is difficult to keep up one’s interest in intellectual matters when friends of the intellectual kind are scarce. However, there are plenty friends not intellectual who serve to bring out the active and practical habits of mind, which overly-intellectual people seldom do. Wherefore, if I am to be up this term, I intend to addict myself rather to the working men who are getting up classes than to pups., who are in the main a vexation. Meanwhile, there is the examination to consider.

“You say Dr. Wilson has sent his book. I will write and thank him. I suppose it is about colour-blindness. I intend to begin Poisson’s papers on electricity and magnetism to-morrow. I have got them out of the library. My reading hitherto has been of novels—‘Shirley’ and ‘The Newcomes,’ and now ‘Westward Ho.’

“Macmillan proposes to get up a book of optics with my assistance, and I feel inclined for the job. There is great bother in making a mathematical book, especially on a subject with which you are familiar, for in correcting it you do as you would to pups.—look if the principle and result is right, and forget to look out for small errors in the course of the work. However, I expect the work will be salutary, as involving hard work, and in the end much abuse from coaches and students, and certainly no vain fame, except in Macmillan’s puffs. But, if I have rightly conceived the plan of an educational book on optics, it will be very different in manner, though not in matter, from those now used.”

The examination referred to was that for a Fellowship at Trinity, and Maxwell was elected on October 10th, 1855.

He was immediately asked to lecture for the College, on hydrostatics and optics, to the upper division of the third year, and to set papers for the questionists. In consequence, he declined to take pupils, in order to have time for reading and doing private mathematics, and for seeing the men who attended his lectures.

In November he writes: “I have been lecturing two weeks now, and the class seems improving; and they come and ask questions, which is a good sign. I have been making curves to show the relations of pressure and volume in gases, and they make the subject easier.”

Still, he found time to attend Professor Willis’s lectures on mechanism and to continue his reading. “I have been reading,” he writes, “old books on optics, and find many things in them far better than what is new. The foreign mathematicians are discovering for themselves methods which were well known at Cambridge in 1720, but are now forgotten.”

The “Poisson” was read to help him with his own views on electricity, which were rapidly maturing, and the first of that great series of works which has revolutionised the science was published on December 10th, 1855, when his paper on “Faraday’s Lines of Force” was read to the Cambridge Philosophical Society.

The next term found him back in Cambridge at work on his lectures, full of plans for a new colour top and other matters. Early in February he received a letter from Professor Forbes, telling him that the Professorship of Natural Philosophy in Marischal College, Aberdeen, was vacant, and suggesting that he should apply.

He decided to be a candidate if his father approved. “For my own part,” he writes, “I think the sooner I get into regular work the better, and that the best way of getting into such work is to profess one’s readiness by applying for it.” On the 20th of February he writes: “However, wisdom is of many kinds, and I do not know which dwells with wise counsellors most, whether scientific, practical, political, or ecclesiastical. I hear there are candidates of all kinds relying on the predominance of one or other of these kinds of wisdom in the constitution of the Government.”

The second part of the paper on “Faraday’s Lines of Force” was read during the term. Writing on the 4th of March, he expresses the hope soon to be able to write out fully the paper. “I have done nothing in that way this term,” he says, “but am just beginning to feel the electrical state come on again.”

His father was working at Edinburgh in support of his candidature for Aberdeen, and when, in the middle of March, he returned North, he found everything well prepared. The two returned to Glenlair together after a few days in Edinburgh, and Maxwell was preparing to go back to Cambridge, when, on the 2nd of April, his father died suddenly.

Writing to Mrs. Blackburn, he says: “My father died suddenly to-day at twelve o’clock. He had been giving directions about the garden, and he said he would sit down and rest a little, as usual. After a few minutes I asked him to lie down on the sofa, and he did not seem inclined to do so; and then I got him some ether, which had helped him before. Before he could take any he had a slight struggle, and all was over. He hardly breathed afterwards.”

Almost immediately after this, Maxwell was appointed to Aberdeen. His father’s death had frustrated some at least of the intentions with which he had applied for the post. He knew the old man would be glad to see him the occupant of a Scotch chair. He hoped, too, to be able to live with his father at Glenlair for one half the year; but this was not to be. No doubt the laboratory and the freedom of the post, when compared with the routine work of preparing men for the Tripos, had their inducements; still, it may be doubted if the choice was a wise one for him. The work of drilling classes, composed, for the most part, of raw untrained lads, in the elements of physics and mechanics was, as Niven says in his preface to the collected works, not that for which he was best fitted; while at Cambridge, had he stayed, he must always have had among his pupils some of the best mathematicians of the time; and he might have founded some ten or fifteen years before he did that Cambridge School of Physicists which looks back with so much pride to him as their master.

Leave-taking at Trinity was a sad task. He writes23 thus, June 4th, to Mr. R.B. Litchfield:—

“On Thursday evening I take the North-Western route to the North. I am busy looking over immense rubbish of papers, etc., for some things not to be burnt lie among much combustible matter, and some is soft and good for packing.

“It is not pleasant to go down to live solitary, but it would not be pleasant to stay up either, when all one had to do lay elsewhere. The transition state from a man into a Don must come at last, and it must be painful, like gradual outrooting of nerves. When it is done there is no more pain, but occasional reminders from some suckers, tap-roots, or other remnants of the old nerves, just to show what was there and what might have been.”

The summer of 1856 was spent at Glenlair, where various friends were his guests—Lushington, MacLennan, the two cousins Cay, and others. He continued to work at optics, electricity, and magnetism, and in October was busy with “a solemn address or manifesto to the Natural Philosophers of the North, which needed coffee and anchovies and a roaring hot fire and spread coat-tails to make it natural.” This was his inaugural lecture.

In November he was at Aberdeen. Letters24 to Miss Cay, Professor Campbell, and C.J. Munro tell of the work of the session. The last is from Glenlair, dated May 20th, 1857, after work was over.

“The session went off smoothly enough. I had Sun, all the beginning of optics, and worked off all the experimental part up to Fraunhofer’s lines, which were glorious to see with a water-prism I have set up in the form of a cubical box, five inch side....

“I succeeded very well with heat. The experiments on latent heat came out very accurate. That was my part, and the class could explain and work out the results better than I expected. Next year I intend to mix experimental physics with mechanics, devoting Tuesday and THURSDAY (what would Stokes say?) to the science of experimenting accurately....

“Last week I brewed chlorophyll (as the chemists word it), a green liquor, which turns the invisible light red....

“My last grind was the reduction of equations of colour which I made last year. The result was eminently satisfactory.”

Another letter,25 June 5th, 1857, also to Munro, refers to the work of the University Commission and the new statutes.

“I have not seen Article 7, but I agree with your dissent from it entirely. On the vested interest principle, I think the men who intended to keep their fellowships by celibacy and ordination, and got them on that footing, should not be allowed to desert the virgin choir or neglect the priestly office, but on those principles should be allowed to live out their days, provided the whole amount of souls cured annually does not amount to £20 in the King’s Book. But my doctrine is that the various grades of College officers should be set on such a basis that, although chance lecturers might be sometimes chosen from among fresh fellows who are going away soon, the reliable assistant tutors, and those that have a plain calling that way, should, after a few years, be elected permanent officers of the College, and be tutors and deans in their time, and seniors also, with leave to marry, or, rather, never prohibited or asked any questions on that head, and with leave to retire after so many years’ service as seniors. As for the men of the world, we should have a limited term of existence, and that independent of marriage or ‘parsonage.’”

It was more than twenty years before the scheme outlined in the above letter came to anything; but, at the time of Maxwell’s death in 1879, another Commission was sitting, and the plan suggested by Maxwell became the basis of the statutes of nearly all the colleges.

For the winter session of 1857–58 he was again at Aberdeen.

The Adams Prize had been established in 1848 by some members of St. John’s College, and connected by them with the name of Adams “in testimony of their sense of the honour he had conferred upon his College and the University by having been the first among the mathematicians of Europe to determine from perturbations the unknown place of a disturbing planet exterior to Uranus.” Professor Challis, Dr. Parkinson, and Sir William Thomson, the examiners, had selected as the subject for the prize to be awarded in 1857 the “Motions of Saturn’s Rings.” For this Maxwell had decided to compete, and his letters at the end of 1857 tell of the progress of the task. Thus, writing26 to Lewis Campbell from Glenlair on August 28th, he says:—

“I have been battering away at Saturn, returning to the charge every now and then. I have effected several breaches in the solid ring, and now I am splash into the fluid one, amid a clash of symbols truly astounding. When I reappear it will be in the dusky ring, which is something like the state of the air supposing the siege of Sebastopol conducted from a forest of guns 100 miles one way, and 30,000 miles the other, and the shot never to stop, but go spinning away round a circle, radius 170,000 miles.”

And again27 to Miss Cay on the 28th of November:—

“I have been pretty steady at work since I came. The class is small and not bright, but I am going to give them plenty to do from the first, and I find it a good plan. I have a large attendance of my old pupils, who go on with the higher subjects. This is not part of the College course, so they come merely from choice, and I have begun with the least amusing part of what I intend to give them. Many had been reading in summer, for they did very good papers for me on the old subjects at the beginning of the month. Most of my spare time I have been doing Saturn’s rings, which is getting on now, but lately I have had a great many long letters to write—some to Glenlair, some to private friends, and some all about science.... I have had letters from Thomson and Challis about Saturn—from Hayward, of Durham University, about the brass top, of which he wants one. He says that the earth has been really found to change its axis regularly in the way I supposed. Faraday has also been writing about his own subjects. I have had also to write Forbes a long report on colours; so that for every note I have got I have had to write a couple of sheets in reply, and reporting progress takes a deal of writing and spelling.”

He devised a model (now at the Cavendish Laboratory) to exhibit the motions of the satellites in a disturbed ring, “for the edification of sensible image-worshippers.”

The essay was awarded the prize, and secured for its author great credit among scientific men.

In another letter, written during the same session, he says: “I find my principal work here is teaching my men to avoid vague expressions, as ‘a certain force,’ meaning uncertain; may instead of must; will be instead of is; proportional instead of equal.”

The death, during the autumn, of his College friend Pomeroy, from fever in India, was a great blow to him; his letters at the time show the depth of his feelings and his beliefs.

The question of the fusion of the two Colleges at Aberdeen, King’s College and the Marischal College, was coming to the fore. “Know all men,” he says, in a letter to Professor Campbell, “that I am a Fusionist.”

In February, 1858, he was still engaged on Saturn’s rings, while hard at work during the same time with his classes. He had established a voluntary class for his students of the previous year, and was reading with them Newton’s “Lunar Theory and Astronomy.” This was followed by “Electricity and Magnetism,” Faraday’s book being the backbone of everything, “as he himself is the nucleus of everything electric since 1830.”

In February, 1858, he announced his engagement to Katherine Mary Dewar, the daughter of the Principal of Marischal College.

“Dear Aunt” (he says,28 February 18th, 1858), “this comes to tell you that I am going to have a wife....

“Don’t be afraid; she is not mathematical, but there are other things besides that, and she certainly won’t stop mathematics. The only one that can speak as an eye-witness is Johnnie, and he only saw her when we were both trying to act the indifferent. We have been trying it since, but it would not do, and it was not good for either.”

The wedding took place early in June. Professor Campbell has preserved some of the letters written by Maxwell to Miss Dewar, and these contain “the record of feelings which in the years that followed were transfused in action and embodied in a married life which can only be spoken of as one of unexampled devotion.”

The project for the fusion of the two Colleges, to which reference has been made, went on, and the scheme was completed in 1860.

The two Colleges were united to form the University of Aberdeen, and the new chair of Natural Philosophy thus created was filled by the appointment of David Thomson, Professor of Natural Philosophy in King’s College, and Maxwell’s senior. Mr. W.D. Niven, in his preface to Maxwell’s works, when dealing with this appointment, writes:—

“Professor Thomson, though not comparable to Maxwell as a physicist, was nevertheless a remarkable man. He was distinguished by singular force of character and great administrative faculty, and he had been prominent in bringing about the fusion of the Colleges. He was also an admirable lecturer and teacher, and had done much to raise the standard of scientific education in the north of Scotland. Thus the choice made by the Commissioners, though almost inevitable, had the effect of making it appear that Maxwell failed as a teacher. There seems, however, to be no evidence to support such an inference. On the contrary, if we may judge from the number of voluntary students attending his classes in his last College session, he would seem to have been as popular as a professor as he was personally estimable.”

The question whether Maxwell was a great teacher has sometimes been discussed. I trust that the following pages will give an answer to it. He was not a prominent lecturer. As Professor Campbell says,29 “Between his students’ ignorance and his vast knowledge it was difficult to find a common measure. The advice which he once gave to a friend whose duty it was to preach to a country congregation, ‘Why don’t you give it them thinner?’ must often have been applicable to himself.... Illustrations of ignotum per ignotius, or of the abstruse by some unobserved property of the familiar, were multiplied with dazzling rapidity. Then the spirit of indirectness and paradox, though he was aware of its dangers, would often take possession of him against his will, and, either from shyness or momentary excitement, or the despair of making himself understood, would land him in ‘chaotic statements,’ breaking off with some quirk of ironical humour.”

But teaching is not all done by lecturing. His books and papers are vast storehouses of suggestions and ideas which the ablest minds of the past twenty years have been since developing. To talk with him for an hour was to gain inspiration for a year’s work; to see his enthusiasm and to win his praise or commendation were enough to compensate for many weary struggles over some stubborn piece of apparatus which would not go right, or some small source of error which threatened to prove intractable and declined to submit itself to calculation. The sure judgment of posterity will confirm the verdict that Clerk Maxwell was a great teacher, though lecturing to a crowd of untrained undergraduates was a task for which others were better fitted than he.