UNIVERSITÉ DE PARIS.

L'Université de Paris est heureuse de vous apporter aujourd'hui ses félicitations et de saluer en vous un Maître éminent de la Physique mathématique et de la Philosophie expérimentale.

Dans votre longue et féconde carrière, si dignement parcourue, vous avez hardiment abordé les questions les plus difficiles de l'Optique, de l'Hydrodynamique, de la Physique solaire et terrestre, et vous les avez résolues avec un égal succès, donnant ainsi l'exemple si rare de la puissance mathématique alliée à l'habileté expérimentale.

L'Optique vous a très souvent attiré. Vous avez suivi dans leur marche les rayons lumineux réfractés dans les corps cristallisés ou réfléchis par les métaux.

Vous avez traité le problème fondamental de la Spectroscopie. Avant vous, les effets mystérieux de la fluorescence semblaient échapper à toute loi; vous nous avez appris la relation qui existe entre les vitesses des vibrations de la lumière émise et de la lumière génératrice. Vous avez appliqué votre analyse pénétrante au calcul de l'aberration de la lumière. Vous avez étudié les causes de la rotation du radiométre. Vous avez heureusement contribué à l'exploration du Soleil par la photographie de la couronne solaire et par la mesure du rayonnement solaire.

Les phénomènes compliquès de l'Hydrodynamique ont attiré votre attention: vous avez su définir l'effet retardateur du gaz ambiant sur le mouvement du pendule, et calculer le coefficient de correction dû à la résistance de l'air.

Récemment encore vous avez contribué à élucider les singulières propriétés des rayons de Rœntgen, en les assimilant à des séries d'impulsions isolées, bien différentes des vibrations périodiques qui constituent la lumière ordinaire.

4, Windsor Terrace, Malahide, Co. Dublin. 4 August, 1881.

Dear Sir John Lubbock,

I got your proof here, which was forwarded from Armagh. I expect to be going there tomorrow. I saw Miss Stokes the day before yesterday, and gave her your message.

I have read your proof, and have made some reference marks, in the margin, numbers enclosed in circles. I also corrected a few misprints which I happened to see. It is no trouble to correct them, and they might be overlooked, especially by the author, who is apt to read a proof as it was meant to be.

In what follows, the numbers refer to the reference marks.

1. A few of the more conspicuous of the fixed lines were discovered by Wollaston near the beginning of the century, by viewing a slit through a prism applied to the naked eye. This observation however remained but little noticed.

2. Long ago, but I have not got the date, and have not reference books here, Fox Talbot showed that the red given to a flame by strontium and the red due to a salt of lithium might be at once distinguished by the prism. I think too, but I am not sure, that he dwelt on the delicacy of this test for the detection of lithium. I do not recollect whether this was before or after 1835 [Wheatstone's experiments]. It is to Kirchhoff and Bunsen that we owe the great impetus that has been given to spectrum analysis, and perhaps it would be proper to mention their names in this connexion; it rather looks as if they had merely applied what had been done by their predecessors.

Trinity College,Oct. 3rd, 1853.

Dear Sir,

What I said about chlorophyll was merely a vague remembrance of one out of a number of facts in Chemistry which Professor Gregory mentioned to me last Winter during a visit to his laboratory. I am very sure that he told me of its isolation but less sure about its colour. He gave me no reference to any source of information and at that time I had no intention of asking for any.

I have written to him on the subject, but I have not yet received an answer.

With respect to my conjecture about Haidinger's brushes, your statement of it is quite accurate and expresses all that deserves the name even of conjecture†. In August 1850 I noted down some experiments and deductions from them, some of which are the same with those which I have since seen described in the fourth part of Moigno's Répertoire d'Optique, particularly the experiment with a plate of quartz.

I have published nothing on the subject. In fact I have had no opportunity of obtaining sufficient foundation for a theory, and a conjecture is best corroborated by the existence of identical or similar conjectures springing up independently.

It has been thought that but slight advantage would arise from attempting any connected description of Sir George Stokes’ scientific work. The published collection of his Mathematical and Physical Papers in five volumes, taken in connexion with the historical analyses by Lord Rayleigh, Lord Kelvin, and others, forms ample material for the mathematician or physicist; while an account, to be interesting to the general reader, would have to be too long. Moreover in his Burnett Lectures on Light, and the other scientific addresses mentioned in the Preface to Vol. v. of his Papers, he has himself gone over much of the ground of his researches, in a manner which forms a model for popular and at the same time accurate exposition.

His scientific relation to the times in which he lived comes out most clearly in his correspondence. It has been felt to be inadvisable to break up the longer series of scientific letters; but some of the shorter groups, and those illustrating the events of his life, are here set forth in order of time, without any attempt at making up a continuous narrative.

A main impression derived from a general survey of his public activity, as revealed by the many thousands of letters that exist, is the state of dependence upon him which was the normal condition, as regards scientific investigations, of most of the numerous Committees of which he was a member.

Vienna, 14 Nov. 1852.

Dear Sir,

I beg leave to introduce myself, and to address you directly. I have read a notice on the interesting crystals with a, metallic surface, you described at the Belfast meeting. I enclose a small portion of crystals I examined some years ago, which I trust will be very interesting to you, as they almost exactly agree with those you examined, except in the point of transparency. The crystals I send are also allied to chinine. They were discovered by Prof. Wöhler, and named Grünes Hydrochinon. To him I have been indebted also for the small portion wrapt up here. The present crystals have evidently the same metallic aspect as those which you described, but they have a deep and beautiful violet blue colour by transmitted light. They are, however, but very faintly translucent, and in no direction they appear colourless or transparent, as it is said in the notice contained in Abbé Moigno's Cosmos 24 Octobre 1852, page 574.—There is also a mode of chemical preparation given there, but I failed in succeeding. Then I believe I can do nothing better, than asking you the favour yourself, in exchange for the small portion of hydrochinon, to send me also a very little quantity of the crystals you examined. Beside the one here included, I have examined a number of other crystals and substances shewing similar phenomena, and I lately drew up a catalogue of them, and presented it to our Academy. I sent a separate copy, inscribed to you, together with a number of others, to our mutual friend, Professor Miller, begging him to forward them to you.

I made acquaintance with Stokes in 1850 at the meetings of the Ray Club. That was a society at Cambridge for the cultivation of Natural Science by friendly intercourse, which had been formed in 1837 in order to fill, so far as that could be done without Henslow's inspiration, the gap left by the cessation of Henslow's weekly receptions of members of the University interested in Natural History. Natural History was still, when I joined the Club, most frequently the subject of conversation at its gatherings, and it may seem surprising that Stokes, who at that time (1850) was best known as a great mathematician, and had just been elected Lucasian professor, should have been a very regular attendant at the weekly meetings of such a Club. Really, however, his bent was to Natural Philosophy, as his work showed, where his great mathematical ability was employed in handling the problems of Nature. His elder brother, William, a fellow of Caius, had been one of the original promoters of the Club, and was a mineralogist and a chemist with whom I fraternised at once; but I very soon found that George Stokes was equally interested in the same subjects, and quite as ready to discuss, with a beginner, questions connected with them on which probably his own conclusions had been reached by a much shorter induction.

The following statement was made by General Sabine, President of the Royal Society, at the Anniversary Meeting, Nov. 30, 1866, in transmitting the Copley Medal to Professor Plücker.

To an audience not exclusively mathematical it is obviously impossible to enter into details of researches which deal with geometrical questions of no ordinary difficulty. Amongst these, however, may be indicated, as especially appreciated by those who are interested in the progress of analytical geometry, his theory of the singularities of plane curves as developed in the “Algebräische Curven,” with its six equations connecting them with the order of the curves: the papers on point and line coordinates, and on the general use of symbols, may also be noticed as establishing his claim to a position in the department of abstract science which is attained by few even of those who give to it their undivided attention. But Professor Plücker has high merits in two other widely different fields of research, viz. in Magnetism and Spectrology: and to these I may more freely invite your attention.

Shortly after Faraday's discovery of the sensibility of bodies generally to the action of a magnet, and of diamagnetism, Professor Plücker, in repeating some of Faraday's experiments, was led to the discovery of magnecrystallic action,—that is, that a crystallized body behaves differently in the magnetic field according to the orientation of certain directions in the crystal.

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.