4, Moreton Square, W.C.

6 July 1861.

My Dear Sir,

I am much gratified by your attention to the condition of the colloidal solutions described in my paper, and shall take an early opportunity to forward a few specimens, as you desire, for your more particular study.

After reflecting upon your remarks I am inclined to think that you will obtain some light from the observation of silicic acid, one of these solutions which has the advantage of being colourless. The liquid condition of all such bodies, it is to be remembered, is not permanent. Now in silicic acid the transition to the gelatinous (solid) form is visibly preceded by a faint opalescence of the liquid. This gradually increases during a few hours or even days, and is sometimes very beautiful. But it is sure to end, sooner or later, in the somewhat sudden solidification of the mass. The previous opalescence may very well be due to suspended solid matter, like Faraday's highly divided gold, as your theory supposes. It is however the effect of an incalculably minute amount of suspended matter, and does not touch the great mass of colloidal matter present. In short the opalescence may be due to suspended matter, although the colloid is truly liquid. Indeed one or two per cent, of such substances generally produce a firm jelly, on passing from the liquid condition, while the solutions operated upon were perfectly limpid with from 3 to 10 per cent, of substance in solution.

That colloids are really in solution appears also to follow from the fact that they are diffusive. They possess the property, and of several the rate has been accurately observed.

Soon after the death of Sir George Stokes, representations were made from various authoritative sources, including Lord Kelvin and Lord Rayleigh, that his papers should be carefully examined; as the experience of his friends and correspondents had shown that he was in possession of valuable improvements and advances in scientific subjects, which had not been adequately published to the world.

Fortunately it had been his custom to preserve all his papers; but for many years they had not been sorted, and their great bulk, as they appeared in the numerous packing cases to which they had been consigned from time to time, demanded an organised plan of attack.

They were in the first place sorted and arranged, after ephemeral printed matter had been rejected, by Mr S. Matthews, the Librarian of the Cambridge Philosophical Society, during the summer of 1902.

It then appeared that the bulk of formal manuscript material that was at all suitable for publication was small. What was found consisted largely of rough sheets containing jottings of arithmetical reductions and calculations, of which the net results had been either published by himself or communicated by letter to other workers. By far the greater part of the material was made up of scientific and official correspondence, amounting probably to more than ten thousand letters and memoranda, in many cases containing matter of high scientific value.

These papers, arranged according to dates and the names of his correspondents, were then further examined and a preliminary selection was made from them.

My father's descent can be traced back to Gabriel or Gaberill Stokes, son of John Stokes, born 1680, who appears to have inherited good brains. He was a well-known engineer of Dublin, where he lived in Essex Street. He suggested a plan for supplying that city with water without the use of pumps, wrote a Treatise on Hydrostatics, and designed the Pigeon-House Wall in the Harbour. He was Deputy Surveyor General for Ireland, and maps exist in the Record Office of Dublin which are countersigned by him.

The history of the Stokes family, previous to 1618, is involved in obscurity. There was a very ancient family of that name who lived in Gloucestershire and owned a good deal of land in that County. Two representatives of that family were living in 1876, Dr Thomas Stokes, of Mailsworth, and his nephew Adrian Stokes, of Southport, both advanced in life and both without issue. Dr T. Stokes possessed an old parchment pedigree, by which his descent could be traced back to the year 1312. It gives the name in different forms as de Stokke, afterwards Stokys. On the tomb of Adam de Stokke in the parish church of Great Bedwyn, Wilts., is the figure of a Crusader with the legs crossed. Dr T. Stokes expressed his belief that the family about whom this memoir is written was a younger branch of his own family. One of the grounds of his opinion was that the Irish branch possessed a seal bearing bezants and a crescent used by Dr John Stokes, Scholar and Fellow of Trinity College, Dublin, not a man likely to use a seal to which he was not entitled.

Lensfield Cottage, Cambridge,

Jan.16th, 1895.

Sir,

I can reply at once, and with much pleasure, to your enquiries.

(1) As to the statement that “recent scientific research has shown the Bible and religion to be untrue,” the answer I should give is simply that the statement is altogether untrue. I know of no sound conclusions of science that are opposed to the Christian religion. There may be wild scientific conjectures put forward by some, chiefly those whose science is only at secondhand, as if they were well-established scientific conclusions, and which may be of such a nature as to involve, on the assumption that they are true, certain religious difficulties; I would not go so far as to speak of opposition, as for the most part religion and science move on such different lines that there is hardly opportunity for opposition.

But if an appearance of opposition may sometimes arise from this cause, it far oftener, I think, arises from the errors of defenders of the faith once delivered to the saints, in putting forward propositions which are mere human accretions to it, and presenting the two as if they had equal claims to acceptance. When I speak of the errors of defenders of the faith I am not thinking of learned theologians of the present day, but rather of those of a bygone age, from whom these human accretions passed into the popular theology, and were supposed to be involved in the Christian faith. This mistaken belief afforded infidels a handle for attacking the faith through the error involved in some of the accretions to it.

69, Albert Street, Regent's Park,

London, N.W.

Jan. 5/57.

I had my first lecture to-day. I got on satisfactorily to myself and I hope interested the men. I shall like my lectures better now for I am coming to electricity which is a more interesting subject to lecture on than mechanics.

At Jermyn St. I got my quarter's salary and found a letter from the Abbé Moigno. It was written to induce me to interest myself in an improvement in printing from a photograph, due to a M. Poitevin (if I have read the name right). The Abbé said that they were endeavouring to place me on the list of candidates for the Corresponding Membership of the French Academy at the coming election. He also called my attention to a paper in Poggendorff by a M. Holtzmann, who had repeated with some variation my experiments on the polarisation of diffracted light, but had arrived at an opposite conclusion as to the direction, of vibration. I went to the Athenseum and looked over Holtzmann's paper. I had not time to read it carefully through as my lecture was coming on. I think I must repeat Holtzmann's experiments and my own, before I can come to a mature judgment on the matter.

…It looked funny to see mathematical formulae in a letter from you. Don't be too ambitious for you will not understand these things. They go much beyond Euclid and Algebra, which will be quite enough for you in the way of pure mathematics; but you may be interested by chemistry and physics.

In reply to a request, made some years ago, for information regarding his collaboration with Prof. Stokes, Sir William Crookes promptly sent a privately printed correspondence extending from Mar. 1876 to April 1879, relating mainly to the radiometer and the viscosity of ramified gases, and also various packets of letters relating to other subjects. His permission to make use of these documents has been fully taken advantage of, only such letters and passages as were of merely temporary interest having been omitted. In spite of the disclaimer in the letter next following, the reader will fully appreciate the value and the joint results of this combination of Sir W. Crookes’ unrivalled experimental skill and bold intuition, with the refined theoretical insight of Sir George Stokes.

Oct. 16, 1904.

My Dear Larmor,

In '76 to '79 I was corresponding with Sir G. Stokes frequently, and as I had the greatest difficulty in making out his writing I sent the letters to my printing office and got the head printer there (who could decipher almost anything) to set them in type. Then after collation and correction so as to get them correct I had a few copies printed off. No one but myself has ever seen them in this form, but now I send them to you—the second man of science who sees them.

These are only a selection; many of minor importance came between. But they serve to show the enormous indebtedness I, in common with most scientific men who corresponded with him, owe to Stokes.

Correspondence With Prof. H. E. ROSCOE.

Owens College, Manchester.

Feb. 24, 1860.

My Dear Mr Stokes,

I am sorry to find that you do not agree with the map of the spectrum I seat—I do not know how the difference can have arisen, for I certainly copied, as correctly as I could, the pencil map you lent me some time ago—which too I returned to you after I had copied it.

If you will allow me to keep your map for a day or two I will draw the map again—keeping the distances the same—so as to correspond with your last.

I found no difficulty in recognising the lines as I drew them. I do not know what became of those between N4 and Q, but I cannot help thinking that they were not contained in the copy you lent me formerly.

Have you seen in the last no. of the Annales de Chimie et de Physique a short note about Kirchhoff's discovery of the probable cause of the coincidence of the bands of light (produced for instance by a soda flame) and the dark lines of the spectrum?

Glasthule Lodge, Kingstown, Ireland,

August 16, 1886.

A happy thought occurred to me to-night as to a mode of adapting the Greenwich Refractor that is to be put to photography. I hope it may solve the difficulty. It is to make the crown-glass, lens of the objective extremely nearly, but not quite, equi-convex, and to mount it in a cell which could be put either way in, the difference of radii of the two surfaces being made to accord with a calculated difference.

For vision, the flatter surface would be turned outwards, and the lenses placed nearly in contact. For photography, the lens would be reversed, and its distance from the flint-glass would be greater than before by a known quantity which would reduce the chromatic correcting power of the flint to what is required for photography.

The separation alone would make the spherical aberration positive, and the reversion alone would make it negative, and if the small difference of radii has the right value these two will compensate each other. Thus the spherical aberration will remain at zero while the chromatic compensation is altered from that suited for vision to that suited for photography.

The focal length of the objective will of course be shortened a little by the separation, but not I think to an inconvenient degree.

38 George Square, Edinburgh,

10/7/86.

My Dear Stokes,

Is Andrews’ paper in type yet? I ask because Mrs Andrews is desirous of getting private copies.

Can you tell me what was the process, finally determined on between you and Andrews, for finding the absolute compressibility of mercury? I am stopped in my pressure work by this very question or, at least, by a question which can be reduced to this. I will gladly make the experiments. Andrews told me some 13 years ago that you and he had decided on a plan,

Yours truly,

P. G. TAIT.

P.S. Might I send you proofs of a paper on “ Kinetic Theory of Gases”? Cayley was kind enough to look at it in MS., but of course I cannot inflict it on him now.

Sylvester spent the day with me, on his way to seek seclusion, for work, at St Andrews.

38 George Square, Edinburgh,

26/12/89.

I had to get De la Rive's book out of the Library to read the passage you referred to. But it seems to me that you have misapprehended my difficulty. Long ago (1880?) you told me about gravity as the cause of the large separation of the electricities :—and, in my lecture of that year, I spoke of you as holding that opinion. I can find a copy for you without trouble.

What I want, and have been seeking for thirty years at least, is the initial cause of the electrification.

Cambridge, Dec.16th, 1850.

Dear Col. Sabine,

Perhaps you may recollect speaking to me once at Prof. Miller's about pendulum experiments. In your paper “On the Reduction to a Vacuum of the Vibrations of an Invariable Pendulum,” Phil. Trans. 1829, in speaking of the results to which you had arrived by a comparison of the vibrations in an exhausted receiver, in air at the atmospheric pressure, and in hydrogen, you add (p. 232) “Should the existence of such a distinct property of resistance, varying in the different elastic fluids, be confirmed by experiments now in progress with other gases, &c.” I have not met with any further notice of these experiments, but you told me on the occasion I have mentioned that the experiments showed that the retardation could not at all be inferred from the density, in passing from one elastic fluid to another.

Now I wish to know (supposing, as I believe is the case, that the experiments have not been published) whether you would have any objection to my stating in a paper read before the Cambridge Philosophical Society that I had been informed by you that the experiments here alluded to fully established the existence of a specific action in elastic fluids quite distinct from mere variations of density.

The paper I allude to was read at the last meeting of the Camb. Phil. Soc. It contains the calculation of the resistance to a pendulum in the two cases of a sphere and of a long cylindrical rod, when the internal friction, as it may be called, of the fluid is taken into account. The agreement of theory with Baily's experiments is very striking.

(From Obituary Notice of Rev. W. V. V. Harcourt, Roy. Soc, Proc, Vol. 20, 1872. By Prof. Phillips?)

Accustomed to the use of the gas-furnace, Mr Harcourt turned it to experiments on transparent compounds of fusion, which might be made to have refractive indices beyond the ordinary ranges, combined with scales of dispersion more favourable to achromaticity. In this he was guided by the trials of Faraday to prepare glass for optical purposes. Many years since, the writer, who was often helpful in this way, ground one of the earliest of the Harcourt glasses into a lens, and found it indeed a highly refractive clear substance, but too much traversed by striæ to be of practical use.

When, some years since, Mr Harcourt removed his residence to the family seat at Nuneham, near Oxford, he constructed furnaces of a different kind for the carrying on of these experiments, and followed them with the zeal, resolution, and patience which had always characterized his firm and well-regulated mind. At an age when most men cease from continuous literary and scientific work, he with failing sight, but perfect memory, was indefatigable in training an assistant and superintending his work; making many new combinations with substances untried before, and now selected for quality of fusion, resistance to atmospheric vicissitudes, range of refraction and specific action on different rays of the spectrum. Thus it was hoped finally to acquire glasses of definite and mutually compensative dispersions, so as to make perfectly achromatic combinations.

§ 1. The object of this communication is to partially realise the hope expressed at the end of my paper of July 1 and July 15, 1889, on the Molecular Constitution of Matter:—“The mathematical investigation must be deferred for a future communication, when I hope to give it with some further developments.” The italics are of present date.

Following the ideas and principles suggested in §§ 14—20 of that paper (referred to henceforth for brevity as “M. C. M.”), let us first find the work required to separate all the atoms of a homogeneous assemblage of a great number n of molecules to infinite distances from one another. Each molecule may be a single atom, or it may be a group of i atoms (similar to one another or dissimilar, as the case may be) which makes the whole assemblage a group of i assemblages, each of n single atoms.

§ 2. Remove now one molecule from its place in the assemblage to an infinite distance, keeping unchanged the configuration of its constituent atoms, and keeping unmoved every atom remaining in the assemblage. Let W be the work required to do so. This is the same for all the molecules within the assemblage, except the negligible number of those (§ 30 below) which are within influential distance of the surface. Hence ½nW is the total work required to separate all the n molecules of the assemblage to infinite distances from one another.

§ 1. My subject this evening is not the physical properties of crystals, not even their dynamics; it is merely the geometry of the structure—the arrangement of the molecules in the constitution of a crystal. Every crystal is a homogeneous assemblage of small bodies or molecules. The converse proposition is scarcely true, unless in a very extended sense of the term crystal (§ 20 below). I can best explain a homogeneous assemblage of molecules by asking you to think of a homogeneous assemblage of people. To be homogeneous every person of the assemblage must be equal and similar to every other: they must be seated in rows or standing in rows in a perfectly similar manner. Each person, except those on the borders of the assemblage, must have a neighbour on one side and an equi-distant neighbour on the other: a neighbour on the left front and an equi-distant neighbour behind on the right, a neighbour on the right front and an equi-distant neighbour behind on the left. His two neighbours in front and his two neighbours behind are members of two rows equal and similar to the rows consisting of himself and his right-hand and left-hand neighbours, and their neighbours' neighbours indefinitely to right and left. In particular cases the nearest of the front and rear neighbours may be right in front and right in rear; but we must not confine our attention to the rectangularly grouped assemblages thus constituted.

In the month of October, 1884, Sir William Thomson of Glasgow, at the request of the Trustees of the Johns Hopkins University in Baltimore, delivered a course of twenty lectures before a company of physicists, many of whom were teachers of this subject in other institutions. As the lectures were not written out in advance and as there was no immediate prospect that they would be published in the ordinary form of a book, arrangements were made, with the concurrence of the lecturer, for taking down what he said by short-hand.

Sir William Thomson returned to Glasgow as soon as these lectures were concluded, and has since sent from time to time additional notes which have been added to those which were taken when he spoke. It is to be regretted that under these circumstances he has had no opportunity to revise the reports. In fact, he will see for the first time simultaneously with the public this repetition of thoughts and opinions which were freely expressed in familiar conference with his class. The “papyrograph” process which for the sake of economy has been employed in the reproduction of the lectures does not readily admit of corrections, and some obvious slips, such as Canchy for Cauchy, have been allowed to pass without emendation; but the stenographer has given particular attention to mathematical formulas, and he believes that the work now submitted to the public may be accepted, on the whole, as an accurate report of what the lecturer said.