Mr. R. Appleyard on Dielectrics. 155 



have been advisable to connect the eight mica condensers in 



parallel ; the deflexions to be observed would then have been 



greater, but the number of tests would have been fewer, and 



there would have been less chance of comparison one with 



another. 



Electrification. — In Table I. the " Elec. p.c." is given for 



paraffin- paper and mica, at the various temperatures. This 



is derived from the galvanometer deflexions taken respectively 



at one minute and two minutes after the application of the 



testing current, thus : — 



toi nil , -i™ i ^rv, l m reading — 2 m reading HrifX 



Elec.% between l m and 2 m = — ^ — r . ^ -s-100. 



l m reading 



Paraffin-paper seems to acquire a minimum Elec. p.c. at 

 about 20° C. ; the reason is not very apparent. 



Charge and Discharge. 



The following figures (Table III.) may be useful as indi- 

 cating the difference between the deflexions obtained in ca- 

 pacity tests, using " charge " and " discharge " deflexions, 

 respectively, for paraffin-paper, mica, gutta-percha, and india- 

 rubber. The deflexions represented by u charge " are not so 

 uniform as the " discharge " readings, that is to say, a repe- 

 tition generally gives a different reading, owing in part per- 

 haps to some of the last charge having remained. This, 

 however, is scarcely to be observed with mica. " Discharge '* 

 readings can generally be reproduced accurately. 



Table III. 





Charge. 



Discharge. 



Charge 

 (repeated). 



Paraffin- paper 



196 

 223 



208 

 198 



196 

 223 



214 

 200-5 



195-5 



223 



[207 1 

 1 210 L 



Mica 



Gutta-percha 



India-rubber 





.210 J 



r 201 i 



197 I 

 198-5 J 



