To C. H. Cay, Esq.

Glenlair, 5th January 1865.

We are sorry to hear you cannot come and see us, but you seem better by your letter, and I hope you will be able for your travels, and be better able for your work afterwards, and not take it too severely, and avoid merimnosity and taking over too much thought, which greatly diminishes the efficiency of young teachers. We have been here since 22d ult., and are in the process of dining the valley in appropriate batches. We have had very rough weather this week, which, combined with the dining, has prevented our usual airings. The ordinary outing is to the Brig of Urr, Katherine on Charlie and I on Darling. Charlie has got a fine band on his forehead, with his name in blue and white beads.

The Manse of Corsock is now finished; it is near the river, not far from the deep pool where we used to bathe.

I set Prof. W. Thomson a prop, which I had been working with for a long time. He sent me 18 pages of letter of suggestions about it, none of which would work; but on Jan 3, in the railway from Largs, he got the way to it, which is all right; so we are jolly, having stormed the citadel, when we only hoped to sap it by approximations.

The prop, was to draw a set of lines like this so that the ultimate reticulations shall all be squares.

The solution is exact, but rather stiff. Now I have a disc A hung by a wire D, between two discs B, C, the interval being occupied by air, hydrogen, carbonic acid, etc., the friction of which gradually brings A to rest. In order to calculate the thickdom or viscosity of the gas, I require to solve the problem above mentioned, which is now done, and I have the apparatus now ready to begin. We are also intent on electrical measurements, and are getting up apparatus, and have made sets of wires of alloy of platinum and silver, which are to be sent all abroad as standards of resistance. I have also a paper afloat, with an electro-magnetic theory of light, which, till I am convinced to the contrary, I hold to be great guns.

Spice[215] is becoming first-rate: she is the principal patient under the ophthalmoscope, and turns her eyes at command, so as to show the tapetum, the optic nerve, or any required part. Dr. Bowman, the great oculist, came to see the sight, and when we were out of town he came again and brought Donders of Utrecht with him to visit Spice.

To H. R Droop, Esq.

Glenlair, Dalbeattie, 19th July 1865.

There are so many different forms in which Societies may be cast, that I should like very much to hear something of what those who have been thinking about it propose as the plan of it.

There is the association for publishing each other’s productions; for delivering lectures for the good of the public and the support of the Society; for keeping a reading room or club, frequented by men of a particular turn; for dining together once a month, etc.

I suppose W——’s object is to increase the happiness of men in London who cultivate physical sciences, by their meeting together to read papers and discuss them, the publication of these papers being only one, and not the chief end of the Society, which fulfils its main purpose in the act of meeting and enjoying itself.

The Royal Society of Edinburgh used to be a very sociable body, but it had several advantages. Most of the fellows lived within a mile of the Society's rooms. They did not need to disturb their dinner arrangements in order to attend.

Many of them were good speakers as well as sensible men, whose mode of considering a subject was worth hearing, even if not correct.

The subjects were not limited to mathematics and physics, but included geology, physiology, and occasionally antiquities and even literary subjects. Biography of deceased fellows is still a subject of papers. Now those who cultivate the mathematical and physical sciences are sometimes unable to discuss a paper, because they would require to keep it some days by them to form an opinion on it, and physical men can get up a much better discussion about armour plates or the theory of glaciers than about the conduction of heat or capillary attraction.

The only man I know who can make everything the subject of discussion is Dr. Tyndall. Secure his attendance and that of somebody to differ from him, and you are all right for a meeting.

If we can take the field with a plan in our head, I dare say we could find a good many men who would co-operate.

We ride every day, sometimes both morning and evening, and so we consume the roads. I have made 68 problems, all stiff ones, not counting riders.

I am now getting the general equations for the motion of a gas considered as an assemblage of molecules flying about with great velocity. I find they must repel as inverse fifth power of distance.

To C. H. Cay, Esq.

Glenlair, 14th October 1865.

... I hope you keep your conscience in good order, and do not bestow more labour on erroneous papers than is useful to the youth who wrote it. Always set him to look for the mistake, if he prefers that to starting fresh, for to find your own mistake may sometimes be profitable, but to seek for another man’s mistake is weariness to the flesh.

There are three ways of learning props.—the heart, the head, and the fingers; of these the fingers is the thing for examinations, but it requires constant practice. Nevertheless the fingers have a fully better retention of methods than the heart has. The head method requires about a mustard seed of thought, which, of course, is expensive, but then it takes away all anxiety. The heart method is full of anxiety, but dispenses with the thought, and the finger method requires great labour and constant practice, but dispenses with thought and anxiety together.

We have had very fine weather since you went away, but I was laid up for more than three weeks with erysipelas all over my head, and got very shaky on my pins. But I have been out for a fortnight, and riding regularly as of old, which is good for Katherine after the nursing, and I eat about double what any man in Galloway does, and know nothing of it in half an hour; but my legs are absorbing the beef as fast as it is administered.

To the Rev. C. B. Tayler.

8 Palace Gardens Terrace, W.,
2d February 1866.

I was very glad to get your kind letter, and to be assured that you still remembered me. I thought of you when I was in Cambridge, and made up my mind to write to you and hear of you and Mrs. Tayler, and your nephew George. A nephew of yours was for a short time in my class in King’s Coll., and I asked him about you, but he had not seen you lately. Is George still in Hull?

You ask for my history since I wrote to you before my marriage. We remained in Aberdeen till 1860, when the union or fusion of the Colleges took place, and I went to King’s Coll., London, where I taught till last Easter, when I was succeeded by W. G. Adams, brother of the astronomer. I have now my time fully occupied with experiments and speculations of a physical kind, which I could not undertake as long as I had public duties. These are the chronological data. It is 13 years nearly since I was with you, and you carried me about when I could not move myself, but I remember everything about you and Otley much better than most things before and after that time. I got advantage from your nursing when my father was ill, and many other things have since brought you and Mrs. Tayler to mind. If you and Mrs. Tayler are to be in London during the spring, we shall be exceedingly glad to see you here, or if you ever go to Scotland in summer or autumn, we hope you will try and stay with us some time. My wife knows you quite well,—that is, as well as I do,—all but what can only be got by seeing and hearing directly, and it would do us both great good to see you, and open up our minds a little.

Many people’s minds seem to be shut up with solemn charms, so that though they seem Christians, and know what they mean to speak about, they can say nothing. At Cambridge I heard several sermons from excellent texts, but all either on other subjects or else right against the text. There is a Mr. Offord in this street, a Baptist[216] who knows his Bible, and preaches as near it as he can, and does what he can to let the statements in the Bible be understood by his hearers. We generally go to him when in London, though we believe ourselves baptized already.

Pray let me hear from you occasionally. We shall be here till the end of March, and after that address Glenlair, Dalbeattie, N.B., which is my permanent address, and is sure at all times to find me.

Mrs. Maxwell joins me in kind regards to you and Mrs. Tayler, and I remain your afft. friend,

J. Clerk Maxwell.

To Professor Lewis Campbell.

Glenlair, Dalbeattie, 3d November 1868.

I have given considerable thought to the subject of the candidature, and have come to the decision not to stand. The warm interest which you and other professors have taken in the matter has gratified me very much, and the idea of following Principal Forbes had also a great effect on my feelings, as well as the prospect of residing among friends; but I still feel that my proper path does not lie in that direction.—Your afft. friend,

J. Clerk Maxwell.

To C. J. Monro, Esq.

Glenlair, Dalbeattie, 6th July 1870.

My question to the Mathematical Society bore fruit in various forms.... It would give my mind too great a wrench just now to go into elliptic integrals, but I will do so when I come to revise about circular conductors. ... I can cut the subject short with an easy conscience, for I have no scruple about steering clear of tables of double entry, especially when, in all really useful cases, convergent series may be used with less trouble, and without any knowledge of elliptic integrals. On this subject see a short paper on Fluid Displacement in next part of the Math. Soc. Trans., where I give a picture of the stream lines, and the distortion of a transverse line as water flows past a cylinder.

Mr. W. Benson, architect, 147 Albany Street, Regent Park, N.W., told me that you had been writing to Nature, and that yours was the only rational statement in a multitudinous correspondence on colours. Mr. Benson considers that Aristotle and I have correct views about primary colours. He has written a book, with coloured pictures, on the science of colour, and he shows how to mix colours by means of a prism. He wants to publish an elementary book with easy experiments, but gets small encouragement, being supposed an heretic. No other architect in the Architect’s Society believes him. This is interesting to me, as showing the chromatic condition of architects. I made a great colour-box in 1862, and worked it in London in ’62 and ’64. I have about 200 equations each year, which are reduced but not published. I have set it up here this year, and have just got it in working order. I expect to get some more material, and work up the whole together. In particular, I want to find any change or evidence of constancy in the eyes of myself and wife during eight years. I can exhibit the yellow spot to all who have it,—and all have it except Col. Strange, F.R.S., my late father-in-law, and my wife,—whether they be Negroes, Jews, Parsees, Armenians, Russians, Italians, Germans, Frenchmen, Poles, etc. Professor Pole, for instance, has it as strong as me, though he is colour-blind; Mathison, also colour-blind, being fair, had it less strongly marked.

One J. J. Müller in Pogg. Ann. for March and April 1870, examines compound colours, and finds the violet without any tendency to red, or the red to blue. He also selects a typical green out of the spectrum.