164 Rood — Electrical Resistance of Glass, Quartz, 



No. 1 



3,400,000 



O Feb. 19th 



Hyg. 18° 



" 2 



3,600,000 



" " 22d 



u 27° 



" 1 



3,700,000 



" March 3d 



" 32° 



" 2 



3,600,000 



(( u 



" 32° 



3,570,000 " 

 Calculating this for one surface of one square centimeter 

 between terminals gives 1,590,000 O. 



Surface resistance of cobalt glass. — From previous experi- 

 ments it was known that the surface resistance of cobalt glass 

 is considerably greater than that of the ordinary varieties of 

 window glass, and the results given below confirm this idea. 

 Four strips were used, with an average length between termi- 

 nals of 4^=™. The experiments were all made on the same day, 

 the hygrometer indicating 34 per cent of moisture. The 

 actual figures obtained are : 



Xo. 1 24,400,000 O Hyg. 34° 

 " 2 21,700,000 " " " 

 " 3 24,400,000 " " " 

 "4 



23,000,000 " 

 Calculating this for one surface of one square centimeter 

 between terminals gives 22,000,000 O. 



Surface resistance of mica. — Four slips of mica were used ; 

 the distance between terminals was 2*5^°' ; the actual figures 

 were : 



No. 1 29,900,000 O Hyg. 35° 

 " 2 25,600,000 " 

 " 3 39,400,000 " 

 '' 4 31,600,000 " 



<( 



il 



(( 



(( 



ff 



u 



31,600,000 " 



Calculating for one surface of one square centimeter, we 

 obtain 50,760,000 II. 



Surface resistance of gutta-percha. — Two slips of the mate- 

 rial were used, the distance between terminals being 1^"^. The 

 actual figures were : 



No. 



1 



17,500,000 



fl 



Feb. 20th 



Hyg. 



17 





2 



18,900,000 





u u 



<( 



u 





I 



13,000,000 





" 28th 



(( 



35 





2 



7,700,000 





(( a 



a 



u 





1 



18,800,000 





March 3d 



ii. 



32 





2 



19,500,000 





(( a 



a 



i( 



16,000,000 " 

 Calculating the mean for o?ie surface of one centimeter 

 between terminals, we have 432,000,000 12. 



