430 



Mr. F. Rutley. 



[May 27, 



References to Dr. Kerr's papers on electro- optics : — 



" Philosophical Magazine," Ser. 4, vol. 50, 1875 ; pp. 337 and 446. 



Ser. 5, vol. 8, 1879; pp. 85 and 229. 



13, 1882 ; pp. 153 and 248. 



Faraday gives a list of bodies with the sign of the electrification 

 they acquired by friction, which is here reproduced for comparison 

 with my results. 



Name of dielectric. 



Sign of the electro - 

 optical effect. 



Sign of electrification 

 by friction. 





+ 



.+ 





+ 



-U 





+ 



+ 





+ 







+ 







+ 







+ 





Resin (dissolved in alcohol) . . 



+ 



































III. " Notes on Alteration induced by Heat in certain Vitreous 

 Rocks ; based on the Experiments of Douglas Herman, 

 F.I.C., F.C.S., and G. F. Rodwell, late Science Master in 

 Marlborough College." By Frank Rutley, F.G.S., 

 Lecturer on Mineralogy in the Royal School of Mines. 

 Communicated by Professor T. G. Bonnet, D.Sc, F.R.S., 

 &c. Received May 18, 1886. 



[Plates 3—5.] 



In this paper an endeavour is made to show the nature of the 

 changes which have resulted from the action of heat upon certain 

 vitreous rocks. The changes which take place in such rocks through 

 natural processes may sometimes be effected by heat alone, at others 

 by heat in presence of moisture. Of these actions the latter is 

 probably the more frequent, but, at the outset, it seems important to 

 ascertain the action simply of dry heat before studying the more 

 complicated conditions engendered by the presence of water and the 

 pressure of superincumbent rock masses. 



