Xl TROCEEDIXGS OF THE GEOLOGICAL SOCIETY. [JunC I9I2, 



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 following 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 

 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 crystallographers, 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 Presnel, Sir William Hamilton, MacCuUagh, 

 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 my 



