182 Reports and Proceedwfj^ — Geological Sociehj — 



accept the Medal this year the Council has desired to place you in company 

 with Bischof, Naumann, Dana, von Hauer, Des Cloiseaux, Story Maskelyne, 

 and von Groth. Succeeding in the Keepership of the Mineralogical Department 

 of the British Museum to the real founder of that Department, and the one who 

 made it an expression of the best side of mineralogical science, you impressed 

 your own personality upon it, and left it more valuable, more useful, more 

 representative, more simple. The last was no light task, and it required, in 

 a mathematician of such high culture and ability, an extraordinary and very 

 unusual type of intellect to write an introduction to the study of minerals, and 

 to arrange a collection to illustrate it, without the use of a single mathematical 

 expression ; and yet to produce a book which is at once intelligible to the 

 museum visitor, a scientitie guide to the student, and a joy to the professed 

 mineralogist. If this were all it would be a great achievement, but you have 

 done as much for the study of rocks and even of meteorites. And all the time 

 you have been engaged in research of a most painstaking and minutely accurate 

 character on the constitution of meteorites and of certain obscure and rare 

 minerals, leaving, with characteristic unselfishness, the more attractive problems 

 to your colleagues. If we add to this your theoretic work on the effect of heat 

 on crystals, your elegant treatment of crystallographic optics, culminating in 

 the conception of the optical indicatrix, your fastidious and dainty choice of 

 expression in order to eliminate the slightest trace of ambiguity from your 

 descriptive work, and, finally, your steadfast devotion to the well-being of the 

 Mineralogical Society, with which you have been so closely identified, we have 

 a record of devotion to your science and duty which has, to the delight of your 

 friends, been worthily crowned by your appointment to the Directorship of our 

 great National Museum of Natural History. 



I ask you to accept the Wollaston Medal, not for the sake of yourself and your 

 work alone, but as a token of acknowledgment by the Science of Geology of 

 part of her debt to the science which you so worthily represent in our country. 



Dr. Fletcher replied in the followiDg words : — 



Mr. President, — I thank the Council very heartily for the distinction that 

 has been conferred upon me by the award of this medal, given more especially, 

 I am told, for my researches in connexion with the crystalline forms and 

 crystal optics. 



Each recipient of the Wollaston Medal must have heard with a thrill of 

 pleasure the news that such a compliment had been paid to him by his fellow- 

 workers ; but doubtless the pleasure has been especially great to the crystallo- 

 graphers, for they cannot but have felt that crystallographic researches deemed 

 worthy of such recognition must have brought some additional honour, however 

 slight, to the memory of the many-sided Wollaston, who, by his invention of the 

 reflective goniometer, had first made possible the measurement of crystalline 

 forms with astronomical precision. 



As regards crystal optics, the subject is too abstruse to appeal to the popular 

 imagination. But, for the mathematician at least, there is wonderful beauty 

 in the thought that, for every biaxal crystal, notwithstanding all our uncertainties 

 relative to the luminiferous ether, to each point on an ellipsoid there corresponds 

 a single ray of light, with three physical characters — namely, the direction and 

 velocity of transmission and the plane of polarization — all definitely and simply 

 related to the geometrical characters of the ellipsoid at that point. I may 

 mention that it was some time after the perception of this relationship before 

 I could convince myself of its truth ; for it seemed that, after the harvest that 

 had been gathered from the wave-surface by Fresnel, Sir William Hamilton, 

 MacCullagh, Sylvester, and others, nothing was left for the gleaner, and that 

 the relationship, if true, would have been discovered long ago. 



It may be not without interest if I add that the direction of iny work in life 

 has been much influenced by two Wollaston Medallists, Professor P. von Groth 

 and the late Professor Maskelyne. In the year 1876, when I was Demonstrator 

 in Physics for Professor Clifton at Oxford, I saw a new book lying on his study 

 table : it was Groth's Pliysikalische Kristallographie , then just published. 



