FROM this point onward the interest of Maxwell’s life (save things “wherewith the stranger intermeddles not”) is chiefly concentrated in his scientific career. As some account of his labours in science will be given in the second portion of this book, what remains of the present narrative is comparatively brief.
The work at King’s College was more exacting than that in Aberdeen. There were nine months of lecturing in the year, and evening lectures to artisans, etc., were recognised as a part of the Professor’s regular duties. Maxwell retained the post until the spring of 1865, when he was succeeded by Professor W. G. Adams, but continued lecturing to the working men during the following winter.
In June 1860 Maxwell attended the British Association’s meeting at Oxford, where he exhibited his box for mixing the colours of the spectrum. He also presented to Section A a most important paper on Bernoulli’s Theory of Gases; a theory which supposes that a gas consists of a number of independent particles moving about among one another without mutual interference, except when they come into collision. Maxwell showed that the apparent viscosity of gases, their low conductivity for heat, and Graham’s laws of diffusion, could be satisfactorily explained by this theory, and gave reasons for believing that in air at ordinary temperature each particle experiences on an average more than 8,000,000,000 collisions per second. It is probable that the contemplation of the “flight of brick-bats” (his own vivid phrase for the constitution of Saturn’s rings) led him on to his far-reaching investigations in this field of molecular physics.
On the 17th of May 1861 he delivered his first lecture before the Royal Institution. The subject was “On the Theory of the three Primary Colours.”
All this while Maxwell was quietly and securely laying the foundations, deep and wide, of his great work on Electricity and Magnetism, but he had not the leisure that was requisite for bringing it to completion.
The period of his King’s College Professorship was far, however, from being scientifically unfruitful. The colour-box was perfected, and many series of observations were made with it. Mrs. Maxwell’s observations were found to have a special value. Through a striking discrepancy between her readings and C. H. Cay’s, Maxwell discovered that the blindness of the Foramen Centrale to blue light, which was strongly marked in his own dark eyes, was either altogether absent from hers, or present in a very low degree. The comparison of J. C. M.’s (J.’s) eyes, and Mrs. M.’s (K.’s) is referred to in Part II.
The experimental measurements by which the present standard of electrical resistance (the Ohm) was first determined, were made at King’s College by a sub-committee of the B.A., consisting of Maxwell, Balfour Stewart, and Fleeming Jenkin, in 1862-63, in accordance with a method proposed by Sir Wm. Thomson. A further experimental measurement was made next year by Maxwell, Fleeming Jenkin, and Charles Hockin (Fellow of St. John’s). The importance of the work may be estimated by the fact that the system of units then determined by the B.A. Committee was, in the main, adopted by the Electrical Congress which met last year (1881) in Paris, and an International Commission has been appointed by the European Governments to make a redetermination of the standard of resistance first measured by the B.A. Committee. Maxwell’s papers on this subject, with those of his fellow-workers, were republished in 1873 in a volume edited by Fleeming Jenkin.[207] Many are the references to successful or fruitless “spins” in the home letters of this period. The following quotation will suffice:—
28th January 1864.
We are going to have a spin with Balfour Stewart to-morrow. I hope we shall have no accidents, for it puts off time so when anything works wrong, and we cannot at first find out the reason, or when a string breaks, and the whole spin has to begin again.... However, we hope to bring out our standards by September, and Becker[208] makes them up excellently.
A mass of correspondence, containing numerous suggestions made by Maxwell from day to day in 1863-4, has been preserved by Professor Jenkin. Two of the least technical passages will be found amongst the letters in this chapter (pp. 337, 340).
Another very important experimental investigation conducted by Maxwell about this period was the determination of the ratio of the electromagnetic and electrostatic units of electricity, for the purpose of comparing this quantity with the velocity of light. As this investigation will be again referred to in Part II., it is only necessary to say here that the experiment amounts to a comparison between the attractions of two electric currents flowing in coils of wire, and the attraction or repulsion between two metal plates which have each received a charge of electricity. Maxwell had pointed out that, in accordance with his theory, the ratio of the units should be equal to the velocity of light, and the value obtained by him was intermediate between the extreme values obtained for that velocity by previous observers. The experiment was the outcome of his theory of the constitution of the space in the neighbourhood of magnetic and electric currents, by which he accounted for all the then known phenomena of magnetism and electricity, and which he published in a semi-popular form in the Philosophical Magazine in 1861 and 1862.
During most of the King’s College time Maxwell resided at 8 Palace Gardens Terrace, Kensington, where he carried on many of his experiments in a large garret which ran the whole length of the house. When experimenting at the window with the colour-box (which was painted black, and nearly eight feet long), he excited the wonder of his neighbours, who thought him mad to spend so many hours in staring into a coffin. This was also the scene of his well-known experiments on the viscosity of gases at different pressures and temperatures. For some days a large fire was kept up in the room, though it was in the midst of very hot weather. Kettles were kept on the fire, and large quantities of steam allowed to flow into the room. Mrs. Maxwell acted as stoker, which was very exhausting work when maintained for several consecutive hours. After this the room was kept cool, for subsequent experiments, by the employment of a considerable amount of ice.
During Maxwell’s residence in London his brother-in-law, the Rev. Donald Dewar, came and stayed in his house in order to undergo a painful operation at the hands of Sir James Ferguson. Maxwell gave up the ground floor of his house to Mr. Dewar and his nurse. He himself, meanwhile, used to take his meals in a very small back room, where frequently he breakfasted (on porridge) on his knees, because there was no room for another chair at the table. Maxwell acted frequently in the capacity of nurse to Mr. Dewar, who would always look out anxiously for his return from college, and whose face would light up with a smile of pleasure and relief when he saw him coming, because he said he knew he should be comfortable when Maxwell returned.
One pleasant incident of his stay in London was the improvement of his acquaintance with Faraday, with whom he seems to have dined on the occasion of his lecture before the Royal Institution in 1861.
On one occasion he was wedged in a crowd attempting to escape from the lecture theatre of the Royal Institution, when he was perceived by Faraday, who, alluding to Maxwell’s work among the molecules, accosted him in this wise—“Ho, Maxwell, cannot you get out? If any man can find his way through a crowd it should be you.”
He also renewed his personal intercourse with Litchfield, Droop, and other Cambridge friends.
His habit at this time was to do his scientific work chiefly in the mornings, unless when entertaining friends, when he would give up his days to them and take hours for work out of the night. In the afternoons he would ride with Mrs. Maxwell. She had been recommended horse exercise in 1860, when the pony “Charlie,” called after Charles Hope Cay, was bought at the Rood fair. He was a high-bred, spirited, light bay Galloway, with arched neck and flowing tail. Maxwell himself broke him in, riding side-saddle, with a piece of carpet to take the place of a habit. This pony was a great favourite until the end in 1879.
About this time (between 1860 and 1865) the endowment of Corsock Church was completed, and the Manse built. Maxwell gave largely to both objects, which were promoted mainly by his zeal and energy.
At the beginning and at the close of the King’s College period Maxwell suffered from two severe illnesses, both of a dangerously infectious nature, and in both of them he was nursed by Mrs. Maxwell. In September 1860 he had an attack of smallpox at Glenlair, which he was supposed to have caught at the fair, where “Charlie” was bought. During this illness his wife was left quite alone with him—the servants only coming to the door of the sick-room. He has been heard to say that by her assiduous nursing on this occasion she saved his life.
The second illness was in September 1865, also at Glenlair. Maxwell had been riding a strange horse, and got a scratch on the head from a bough of a tree; this was followed by an attack of erysipelas, which brought him very low. Mrs. Maxwell was again his nurse, and to listen, as he insisted on doing, to her quiet reading of their usual portion of Scripture every evening, was the utmost mental effort which he could bear.
The years which followed the resignation of his post at King's College were spent, for the most part, at Glenlair, the house being at this time enlarged in general accordance with his father’s plan. And Maxwell took advantage of this retirement to embody some of the results of his investigations in substantive books. The great work on Electricity and Magnetism, although not published till 1873, was now taking definite shape, and the treatise on Heat, which appeared in 1870, had been undertaken as a by-work during the same period.
His scientific and other correspondence also took up a good deal of energy. Some measure of it is afforded by the fact that a “pillar”-box was let into the rough stone wall on the roadside, across the Urr, for the sole use of Glenlair House. Maxwell would himself carry the letters to and from this rustic post-office in all weathers, at the same time giving the dogs a run.
Both now and afterwards, his favourite exercise—as that in which his wife could most readily share—was riding, in which he showed great skill. Mr. Fergusson remembers him in 1874, on his new black horse, “Dizzy,” which had been the despair of previous owners, “riding the ring,” for the amusement of the children at Kilquhanity, throwing up his whip and catching it, leaping over bars, etc.
A considerable portion of the evening would often be devoted to Chaucer, Spenser, Milton, or a play of Shakespeare, which he would read aloud to Mrs. Maxwell.
On Sundays, after returning from the kirk, he would bury himself in the works of the old divines. For in theology, as in literature, while reckoning frankly with all phases, his sympathies went largely with the past. Not that he would have checked the real progress of thought on the subject of religion, but he did not share the sanguine hopes of some who have sought to hasten these “slow-paced” changes; nor did he believe in progress by ignoring differences, or by merging the sharp outlines of traditional systems in the haze of a “common Christianity.” He was one of those in whom physical studies seem to have the effect of leading the mind to dwell on the permanent aspects of thought as well as of things, thus reinforcing the instincts of conservatism. No mind ever delighted more in speculation, and yet none was ever more jealous of the practical application or the popular dissemination of what appeared to him as crude and half-baked theories about the highest subjects. He preferred resting on the great thoughts of other ages, though no man knew better wherein they (and scientific theories likewise) fell short of certainty; and while he was anything rather than a formalist or a dogmatist, and still clung to the belief that love remains while knowledge vanishes away, he was the enemy of indefiniteness and indifferentism, as well as of a style of preaching which, as he used to say, “dings ye wi mere morality.” His theological attitude, which it would be rash to develop further here, is indicated to some extent in his letter to Bishop Ellicott, and in his reply to the Secretary of the Victoria Institute, both of which will be found in Chapter XII (pp. 393, 404).
But he was far, indeed, from judging men by their opinions. “I have no nose for heresy,” he used to say. His sympathy pierced beneath the outer shell of circumstance and association, and he hardly ever failed to discover what was best and strongest in those with whom he had to do.
His kindly relations with his neighbours and with their children may be passed without further notice after what has been said above. But it may be mentioned that he used occasionally to visit any sick person in the village, and read and pray with them in cases where such ministrations were welcomed.
One who visited at Glenlair between 1865 and 1869 was particularly struck with the manner in which the daily prayers were conducted by the master of the household. The prayer, which seemed extempore, was most impressive and full of meaning.[209]
It is right also to record briefly his continued intercourse with his cousins of the Cay family. Mr. William Dyce Cay, who had now entered on his profession as a civil engineer, was employed by him to build the bridge over the Urr, and has a vivid recollection of their intercourse, both then (1861-2) and in former years. In particular he remembers how, on one occasion, Maxwell spent the whole time during a walk of several miles over the hill from Glenlair to Parton, “giving one example after another to explain by illustration the principle of virtual velocities.” ... “The feeling I had,” says Mr. Cay, “was that before I got to the bottom of one example he had rushed off to another.”
And the reader will find in the correspondence two of Maxwell’s letters to my friend Charles Hope Cay, and in another letter a few words of bright description of him. He died in 1869, at the early age of twenty-eight, the most devoted of teachers, one of the purest-hearted and most amiable of men. If he could have listened to his cousin’s gentle warnings against excessive zeal, perhaps his services to Clifton College, if less vividly remembered, might have been continued longer. But who knows? “They whom the gods love die young.”
Maxwell’s retirement was not by any means unbroken. There was a visit to London in the spring of every year. And in the spring and early summer of 1867 he made a tour in Italy with Mrs. Maxwell. They had the misfortune to be stopped for quarantine at Marseilles, and his remarkable power of physical endurance and of ministration were felt by all who shared in the mishap. True to the associations of his early days (see above, pp. 28, 121), he became the general water-carrier, and in other ways contributed greatly to the alleviation of discomforts that were by no means light.
We met accidentally at Florence, and I remember his mentioning two things as having particularly struck him amongst the innumerable objects of interest at Rome. He had looked at the dome of St. Peter's with an eye of sympathetic genius,[210] and his ear for melody had been satisfied by “the Pope's band.” He acquired Italian with great rapidity, and amused himself with noticing the different phonetic values of the letters in Italian and English.[211] One of his chief objects in learning the language was to be able to converse with Professor Matteucci, whose bust now stands in the Campo Santo at Pisa. During the same tour he took special pains to improve his acquaintance with French and German. The only language he had any difficulty in mastering was Dutch.
In the years 1866, 1867, 1869, and 1870, he was either Moderator or Examiner in the Mathematical Tripos at Cambridge, where his influence was more and more felt. His work on these occasions was, indeed, a principal factor in the movement, to be hereafter described, which led ultimately to important changes in the Examination system; to the creation of the Cavendish Laboratory; and to the foundation of the Chair of Experimental Physics.
His paper on the Viscosity of Gases, printed in the Phil. Trans. for 1866, had been delivered by him as the Bakerian Lecture for that year.
He also attended several meetings of the British Association, and, in 1870, at the Liverpool meeting, was President of Section A (Mathematics and Physics). His Presidential Address was on the relation of Mathematics and Physics to each other—a theme suggested by Professor Sylvester, who had been president of the same section in the previous year. The opening passage, in which he alludes to other recent scientific addresses, is characteristic; and may be quoted here:—
I have endeavoured to follow Mr. Spottiswoode, as with far-reaching vision he distinguishes the systems of science into which phenomena, our knowledge of which is still in the nebulous stage, are growing. I have been carried, by the penetrating insight and forcible expression of Dr. Tyndall, into that sanctuary of minuteness and of power, where molecules obey the laws of their existence, clash together in fierce collision, or grapple in yet more fierce embrace, building up in secret the forms of visible things. I have been guided by Professor Sylvester towards those serene heights
But who will lead me into that still more hidden and dimmer region where Thought weds Fact,—where the mental operation of the mathematician and the physical action of the molecules are seen in their true relation? Does not the way to it pass through the very den of the metaphysician, strewed with the remains of former explorers and abhorred by every man of science? ...
Two important papers read by Maxwell at the same meeting were that “On Hills and Dales,” to which reference will be found in the correspondence (pp. 382, 383), and that “On Colour Vision at different Points of the Retina.”
The Cambridge examinations were the only cause which separated him for more than a day or two from Mrs. Maxwell. When most pressed with the load of papers to be read, he would write to her daily—sometimes twice a day—in letters full of “enfantillages,” as in his boyish endeavours to amuse his father, telling her of everything, however minute, which, if she had seen it, would have detained her eye, small social phenomena, grotesque or graceful (including the dress of lady friends), together with the lighter aspects of the examinations; College customs, such as the “grace-cup;” his dealings with his co-examiners, and marks of honour to himself which he knew would please her, though they were indifferent to him. And sometimes he falls into the deeper vein, which was never long absent from his communion with her, commenting on the portion of Scripture which he knew that she was reading, and passing on to general meditations on life and duty.
In November 1868 his old teacher, James D. Forbes, had resigned the principalship of the United College in the University of St. Andrew's, and an effort was made by several of the professors[212] to induce Maxwell to stand for the vacant post, which was in the gift of the Crown, and had been held by Brewster and Forbes successively. He was touched by the kindness, and travelled a whole day from Galloway to confer with us, but, on mature consideration, relinquished the idea.
Letters, 1860 to 1870.
To Rev. Lewis Campbell.
Marischal College,
Aberdeen, 5th January 1860.
... I have been publishing my views about Elastic Spheres in the Phil. Mag. for Jany., and am going to go on with it as I get the p r o p Superscript n s, written out. I have also sent my experiments on Colours to the Royal Society of London, so I have two sets of irons in the fire, besides class work. I hope you get on with Plato, and that your pupils are all Theætetuses, and that wisdom soaks like oil into their inwards. There is a man here who is striving after a general theory of things, but he has great difficulty in so churning his thoughts as to coagulate and solidify the vague and nebulous notions which wander in his head. He has been applying to me very steadily whenever he can pounce on me, and I have prescribed for him as I best could, and I hope his abstract of his general theory of things will be palatable to the readers of the British Ass. Reports for 1859.
To his Wife.
Edinburgh, 13th April 1860.
How let us read (2 Cor.) chapter XII., about the organisation of the Church, and the different gifts of different Christians, and the reason of these differences that Christ’s body may be more complete in all its parts. If we felt more distinctly our union to Christ, we would know our position as members of His body, and work more willingly and intelligently along with all the rest in promoting the health and growth of the body, by the use of every power which the spirit has distributed to us.
Let us read about charity,—that love which is so perfect that it remains when that which is in part shall be done away. May God purify our love, and make it fit for eternity, by grafting upon it the love of Himself, that so both the human root and the engrafted branches and the divine fruit may be holy to Him!
From C. J. Monro, Esq.
Hadley, Barnet, N.
23d October 1861.
Thank you much for the papers. That about vortices I had skimmed already in the magazine. I shall now be able to do more than skim it. The coincidence between the observed velocity of light and your calculated velocity of a transverse vibration in your medium seems a brilliant result. But I must say I think a few such results are wanted before you can get people to think that, every time an electric current is produced, a little file of particles is squeezed along between rows of wheels. But the instances of bodily transfer of matter in the phenomena of galvanism look like it already, and I admit that the possibility of convincing the public is not the question.
To H. B. Droop, Esq. (of the Equity Bar).
Glenlair, Dalbeattie, N.B., 28th December 1861.
I enclose a short statement of the scheme of endowing the chapel which was built near us in 1838 for this district, which is very far from any parish church. If we can raise £1000, there is a fund already raised which will contribute £2000, so as to give a salary of £120 to the minister permanently, and as the people are too poor to support the minister themselves, we hope to make the chapel independent of chance contributions in this way. Great part of the funds for building the church were subscribed in London by all kinds of people who were friends of an English gentleman who then had property here; but we have no longer any such means of drawing on the metropolis.
If you can put us in the way of diminishing the deficit we shall be grateful, and I will see that the money goes to the fund, and that the names are duly entered, however small the contributions.
... I have nothing to do in King’s College till Jany. 20, so we came here to rusticate. We have clear hard frost without snow, and all the people are having curling matches on the ice, so that all day you hear the curling-stones on the lochs in every direction for miles, for the large expanse of ice vibrating in a regular manner makes a noise which, though not particularly loud on the spot, is very little diminished by distance. I am trying to form an exact mathematical expression for all that is known about electro-magnetism without the aid of hypothesis, and also what variations of Ampère’s formula are possible, without contradicting his expressions. All that we know is about the action of closed currents—that is, currents through closed curves. Now, if you make a hypothesis (1) about the mutual action of the elements of two currents, and find it agree with experiment on closed circuits, it is not proved, for—
If you make another hypothesis (2) which would give no action between an element and a closed circuit, you may make a combination of (1) and (2) which will give the same result as (1). So I am investigating the most general hypothesis about the mutual action of elements, which fulfils the condition that the action between an element and a closed circuit is null. This is the case if the action between two elements can be reduced to forces between the extremities of those elements depending only on the distance and + or — according as they act between similar or opposite ends of the elements. If the force is an attraction equals phi left parenthesis r right parenthesis s s prime left parenthesis cosine omega plus 2 cosine theta cosine theta prime right parenthesis where omega is the angle between s and s prime, r the distance of s and s prime and theta and theta prime the angles s and s prime, the elements, make with r, then the condition of no action will be fulfilled.
To the Same.
8 Palace Gardens Terrace, W.,
24th January 1862.
... When I wrote to you about closed currents, it was partly to arrange my own thoughts by imagining myself speaking to you. Ampère’s formula containing n and k is the most general expression for an attractive or repulsive force in the line joining the elements; and I now find that if you take the most general expression consistent with symmetry for an action transverse to that line, the resulting expression for the action of a closed current on an element gives a force not perpendicular to that element. Now, experiment 3d (Ampère) shows that the force on a movable element is perp. to the directions of the current, so that I see Ampère is right.
But the best way of stating the effects is with reference to “lines of magnetic force.” Calculate the magnetic force in any plane, arising from every element of the circuit, and from every other magnetising agent, then the force on an element is in the line perp. to the plane of the element and of the lines of force.
But I shall look up Cellerier and Plann, and the long article in Karsten’s Cyclopœdia. I want to see if there is any evidence from the mathematical expressions as to whether element acts on element, or whether a current first produces a certain effect in the surrounding field, which afterwards acts on any other current.
Perhaps there may be no mathematical reasons in favour of one hypothesis rather than the another.
As a fact, the effect on a current at a given place depends solely on the direction and magnitude of the magnetic force at that point, whether the magnetic force arises from currents or from magnets. So that the theory of the effect taking place through the intervention of a medium is consistent with fact, and (to me) appears the simplest in expression; but I must prove either that the direct action theory is completely identical in its results, or that in some conceivable case they may be different. My theory of the rotation of the plane of polarised light by magnetism is coming out in the Phil. Mag. I shall send you a copy.
To the Same.
8 Palace Gardens Terrace,
Kensington, London, W. 28th January 1862.
Some time ago, when investigating Bernoulli’s theory of gases, I was surprised to find that the internal friction of a gas (if it depends on the collision of particles) should be independent of the density.
Stokes has been examining Graham’s experiments on the rate of flow of gases through fine tubes, and he finds that the friction, if independent of density, accounts for Graham’s results, but, if taken proportional to density, differs from those results very much. This seems rather a curious result, and an additional phenomenon, explained by the “collision of particles” theory of gases. Still one phenomenon goes against that theory—the relation between specific heat at constant pressure and at constant volume, which is in air = 1·408, while it ought to be 1·333.
My brother-in-law, who is still with us, is getting better, and had his first walk on crutches to-day across the room.
To C. J. Monro, Esq.
8 Palace Gardens Terrace,
London W., 18th February 1862.
(Recd. 3d March)
I got your letter in Scotland, whither we had gone for the Christmas holidays. I have been brewing Platonic suds, but failed, owing I suppose to a too low temperature. I had not read Plateau’s recipe then. Some of the bubbles on the surface lasted a fortnight in the air, but they were scummy and scaly and inelastic. I shall take more care next time. Elliot of the Strand (30) is going to produce colour-tops, with papers from De La Rue, and directions for use by me; and so I shall be put in competition with the brass Blondin and the Top on the top of the Top.
... With regard to Britomart’s nurse—I have not Spenser here, but I think Spenser was not a magician himself, and got all his black art out of romances and not out of the professional treatises,—the notions to be brought out were:—1st, The unweaving any web in which B. had been caught; 2d, Doing so in witch-like fashion; 3d, Not like a wicked witch, but like a well-intentioned nurse, unused to the art, and therefore blunderingly. She believes in the number three and in contrariety, and therefore says everything thrice and does everything thrice, saying inversions of sentences, and doing reversions of her revolutions, which are described in similar language. The revolutions begin by + 3 (2p i) against the visible motion of the sun, then by a revolution - (6p i) she returns all contrary and unweaves the first. Then she goes round + (6p i), to make the final result contrary to the natural revolution, and to make a complete triad. Withershins is, I believe, equivalent to wider die Sonne in High Dutch, which I am not aware is a modern or ancient idiom in that language, but it may be one in a cognate language. If the “phamplets” have not turned up in Madeira yet, let me know, that I may “replace” them.
I suppose in your equations, when the numbers do not amount to unity, Black has been present. dot 841 Brunsw period normal upper G plus dot 159 normal upper W equals dot 200 normal upper V plus dot 423 normal upper U plus dot 377 Black period
That is, green a little palish and dark mauve, your last equation by the young eyes. It is something like a colour-blind e q Superscript normal n, but all those I know say 100 Brunswick G = 100 Vermillion, so that this person sees the green darker than the Vermillion, or in other words sees much more of the second side of the equation than a colour-blind person would. But in twilight normal upper U comes out strong, while normal upper G does not; so that I think the apparent equality arises from suppression of all colours but blue (in normal upper U and normal upper U) in the twilight, so that you may write— dot 841 Black plus dot 159 normal upper W equals dot 577 Black plus dot 423 normal upper U
There is no use going to the 3 Superscript rd period place of decimals, unless you spend a good while on each observation, and have first-rate eyes. But if you can get observations to be consistent to the 3 Superscript rd period place of decimals, glory therein, and let me know what the human eye can do.
Donkin gave me tea in Oxford, July 1, 1860.
I find that my belief in the reality of State affairs is no greater in London than in Aberdeen, though I can see the clock at Westminster on a clear day. If I went and saw the parks of artillery at Woolwich, and the Consols going up and down in the city, and the Tuscarora and Mr. Mason, I would know what like they were, but otherwise a printed statement is more easily appropriated than experience is acquired by being near where things are being transacted.
I am getting a large box made for mixture of colours. A beam of sunlight is to be divided into colours by a prism, certain colours selected by a screen with slits. These gathered by a lens, and restored to the form of a beam by another prism, and then viewed by the eye directly. I expect great difficulties in getting everything right adjusted, but when that is done I shall be able to vary the intensity of the colours to a great extent, and to have them far purer than by any arrangement in which white light is allowed to fall on the final prism.
I am also planning an instrument for measuring electrical effects through different media, and comparing those media with air. A and B are two equal metal discs, capable of motion towards each other by fine screws; D is a metal disc suspended between them by a spring, C; E is a piece of glass, sulphur, vulcanite, gutta-percha, etc. A and B are then connected with a source of + electricity, and D with - electricity. If everything was symmetrical, D would be attracted both ways, and would be in unstable equilibrium, but this is rendered stable by the elasticity of the spring G. To find the effect of the plate E, you work A further or nearer till there is no motion of D consequent on electrification. Then the plate of air between A and D is electrically equivalent to the two plates of air and one of glass (say) between D and B, whence we deduce the c o e f f Superscript normal t period for E.
To Rev. Lewis Campbell.
8 Palace Gardens Terrace,
Kensington, W, 21st April 1862.
It is now a long time since I wrote half a letter to you, but I have never since had time to write or to find the scrap. I suppose, as it was more than a good intention, but less than a perfect act, it may be regarded as destined to paper purgatory. This is the season of work to you, when folks visit shrines in April and May, but I get holiday this week. I have been putting together a large optical box, 10 feet long, containing two prisms of bisulphuret of carbon, the largest yet made in London, five lenses and two mirrors, and a set of movable slits. Everything requires to be adjusted over and over again if one thing is not quite right placed, so I have plenty of trial work to do before it is perfect, but the colours are most splendid.
I think you asked me once about Helmholtz and his philosophy. He is not a philosopher in the exclusive sense, as Kant, Hegel, Mansel are philosophers, but one who prosecutes physics and physiology, and acquires therein not only skill in discovering any desideratum, but wisdom to know what are the desiderata, e.g., he was one of the first, and is one of the most active, preachers of the doctrine that since all kinds of energy are convertible, the first aim of science at this time should be to ascertain in what way particular forms of energy can be converted into each other, and what are the equivalent quantities of the two forms of energy.
The notion is as old as Descartes (if not Solomon), and one statement of it was familiar to Leibniz. It was wholly unknown to Comte, but all sorts of people have worked at it of late,—Joule and Thomson for heat and electricals, Andrews for chemical combinations, Dr. E. Smith for human food and labour. We can now assert that the power of our bodies is generated in the muscles, and is not conveyed to them by the nerves, but produced during the transformation of substances in the muscle, which are supplied fresh by the blood.
We can also form a rough estimate of the efficiency of a man as a mere machine, and find that neither a perfect heat engine nor an electric engine could produce so much work and waste so little in heat. We therefore save our pains in investigating any theories of animal power based on heat and electricity. We see also that the soul is not the direct moving force of the body. If it were, it would only last till it had done a certain amount of work, like the spring of a watch, which works till it is run down. The soul is not the mere mover. Food is the mover, and perishes in the using, which the soul does not. There is action and reaction between body and soul, but it is not of a kind in which energy passes from the one to the other,—as when a man pulls a trigger it is the gunpowder that projects the bullet, or when a pointsman shunts a train it is the rails that bear the thrust. But the constitution of our nature is not explained by finding out what it is not. It is well that it will go, and that we remain in possession, though we do not understand it.
Hr. Clausius of Zurich, one of the heat philosophers, has been working at the theory of gases being little bodies flying about, and has found some cases in which he and I don’t tally, so I am working it out again. Several experimental results have turned up lately, rather confirmatory than otherwise of that theory.
I hope you enjoy the absence of pupils. I find that the division of them into smaller classes is a great help to me and to them; but the total oblivion of them for definite intervals is a necessary condition of doing them justice at the proper time.
To Fleeming Jenkin, Esq.[213]
27th Aug. 1863.
... To compare electromagnetic with electrostatic units:—
1st, Weber’s method.—Find the capacity of a condenser in electrostatic measure (meters).
Determine its potential when charged, and measure the charge of discharge through a galvanometer.
2d, Thomson’s.—Find the electromotive force of a battery by electromagnetic methods, and then weigh the attraction of two surfaces connected with the two poles.
3d, (Not tried, but talked of by Jenkin).—Find the resistance of a very bad conductor in both systems—
(1) By comparison with (4th June),
(2) By the log. decrement of charge per second.
All the methods require a properly graduated series of steps. The 1st and 2d determine V, a velocity = 310,740,000 meters per second.
The 3d method determines normal upper V squared.
The first method requires a condenser of large capacity, and the measurement of this capacity and that of the discharge by a galvanometer.
I think this method looks the best; but I would use a much larger condenser than Weber, and determine its capacity by more steps.
The chief difficulty of Thomson’s method is the measurement of a very small force and a very small distance. I think these difficulties may be overcome by making the force act on a comparatively stiff spring and magnifying optically the deflection.
On the third method we require a very large condenser indeed, also a series of resistances in steps between 4th June and that of the insulating substance of the condenser, and a galvanometer (or electrometer) to measure discharge (or tension)....
To C. H. Cay, Esq.
8 Palace Gardens Terrace,
18th November 1863.
We hope to hear how you are. A little literature helps to chase away mathematics from the mind. I have read Paracelsus in parts, but concluded that there was a great deal of poetry in it; but Mr. Browning has written much better poems with half the quantity of poetry at his disposal. Have you seen Pessimus, a Prose Poem in Paradox, from Oxford, and Sketch from Cambridge by a Don who imagines that mathematical men are safer not to talk shop than classical. I know several men who see all nature in symbols, and express themselves conformably whether in Quintics or Quantics, Invariants or Congruents. I send you the electric scheme.
To his Wife.
22d June 1864.
May the Lord preserve you from all evil, and cause all the evil that assaults you to work out His own purposes, that the life of Jesus may be made manifest in you, and may you see the eternal weight of glory behind the momentary lightness of affliction, and so get your eyes off things seen and temporal, and be refreshed with the things eternal! How love is an eternal thing, and love between father and son or husband and wife is not temporal if it be the right sort, for if the love of Christ and the Church be a reason for loving one another, and if the one be taken as an image of the other, then, if the mind of Christ be in us, it will produce this love as part of its complete nature, and it cannot be that the love which is first made holy, as being a reflection of part of the glory of Christ, can be any way lessened or taken away by a more complete transformation into the image of the Lord.
I have been back at 1 Cor. XIII. I think the description of charity or divine love is another loadstone for our life—to show us that this is one thing which is not in parts, but perfect in its own nature, and so it shall never be done away. It is nothing negative, but a well-defined, living, almost acting picture of goodness; that kind of it which is human, but also divine. Read along with it 1 John IV., from verse 7 to end; or, if you like, the whole epistle of John and Mark XII. 28.
To the Same.
23d June 1864.
Think what God has determined to do to all those who submit themselves to His righteousness and are willing to receive His gift. They are to be conformed to the image of His Son, and when that is fulfilled, and God sees that they are conformed to the image of Christ, there can be no more condemnation, for this is the praise which God Himself gives, whose judgment is just. So we ought always to hope in Christ, for as sure as we receive Him now, so sure will we be made conformable to His image. Let us begin by taking no thought about worldly cares, and setting our minds on the righteousness of God and His kingdom, and then we shall have far clearer views about the worldly cares themselves, and we shall be continually enabled to fight them under Him who has overcome the world.
To the Same.
26th June 1864.
Note in (2 Cor.) ver. 10 that the judgment is according to what we have done, so that if we are to be counted righteous, we must really get righteousness and do it. Note also that we are to receive the things done in the body, not rewards or punishments merely, but the things themselves are to be brought back to us, and we must meet them in the spirit of Christ, who bore our sins and abolished them, or else we must be overwhelmed altogether.
... I have come from Mr. Baptist Noel. The church was full to standing, and the whole service was as plain as large print. The exposition was the Parable of Talents, and the sermon was on John III. 16. The sermon was the text writ large, nothing ingenious or amusing, and hardly any attempt at instruction, but plain and very serious exhortation from a man who evidently believes neither more nor less than what he says.
To the Same.
28th June 1864.
I can always have you with me in my mind—why should we not have our Lord always before us in our minds, for we have His life and character and mind far more clearly described than we can know any one here? If we had seen Him in the flesh we should not have known Him any better, perhaps not so well. Pray to Him for a constant sight of Him, for He is man that we may be able to look to Him, and God, so that He can create us anew in His own image.
To C. Hockin, Esq.
Glenlair, Dalbeattie, September 7th 1864.
... I have been doing several electrical problems. I have got a theory of “electric absorption,” i.e. residual charge, etc., and I very much want determinations of the specific induction, electric resistance, and absorption of good dielectrics, such as glass, shell-lac, gutta-percha, ebonite, sulphur, etc.
I have also cleared the electromagnetic theory of light from all unwarrantable assumption, so that we may safely determine the velocity of light by measuring the attraction between bodies kept at a given difference of potential, the value of which is known in electromagnetic measure.
I hope there will be resistance coils at the British Association.
To Professor Lewis Campbell.[214]
8 Palace Gardens Terrace,
London, W., 22d November 1864.
It was very kind of you to think of me at this time, and write to me. I shall always remember your mother’s kindness to me, beginning more than twenty-three years ago, and how she made me the same as you two when I came to see you. To you her memory is what you can share with none, so I can say no more except that you will continue to find that to have had a mother so devoted to her duty gives you a consciousness of your own obligations which will be strengthened whenever you think of her.