1884.] 



On the Electrical Qualities of Glass. 



489 



described in the second paper referred to, and the chemical analyses 

 of the specimens experimented on, that in the case of flint glass, the 

 electrical resistance increased with the density, and on the other hand 

 that for potash or soda-lime glass, the resistance increased as the 

 glass seemed to approach in composition to a definite chemical 

 compound. Density, chemical composition, and resistance appeared 

 all to be so related to one another in the case of the flint glasses 

 experimented on, that increase of density, as well as approach to 

 defmiteness of composition, gave increase of resistance. 



We offer the present paper as a contribution towards the further 

 elucidation of this question. The experiments which are here 

 described were carried out on glasses which differed considerably 

 from those previously used. They were all flint glasses of consider- 

 able density, and it will be seen that though they differ widely in 

 specific resistance, not one can be called a bad glass for electrical 

 purposes. No experiments were made on potash and soda-lime 

 glasses, as these are generally low in resistance, and our first object 

 was to obtain definite information regarding comparatively dense 

 glasses which former experiments show to be relatively much better 

 insulators. It is our intention, however, in a continuation of the 

 present research, to experiment both as to resistance and specific 

 inductive capacity on lime glasses of varying composition. 



Fig. 1. 



The density of each specimen was carefully determined, and a 

 complete chemical analysis made. The electrical experiments were 

 made in the physical laboratory of the University of Glasgow, and 

 the same general plan was followed as described in the paper 

 mentioned above (" Proe. Roy. Soc," vol. 34, p. 199). The 

 arrangement of apparatus, with the exception of reversing key, &c, 



