﻿Mr. Rollo Appleyard on Dielectrics. 397 



to quality, if the general history of the material and the 

 peculiarities of manufacture are understood. But, apart from 

 its merely commercial bearing, " electrification '' presents a 

 wide field for scientific research. The use of the term " elec- 

 trification" for this rate of change of the apparent resistance 

 of a dielectric with the time of application of the charging 

 current, may be called into question by those who prefer the 

 words u polarization," or "absorption;" but, in the present 

 stage of our knowledge of the action which determines this 

 change, it has been thought better to adopt a term which is 

 never mistaken in practice than to use an ambiguous ex- 

 pression, founded upon an equally uncertain hypothesis. 

 " Electrification w seems to be the net result of many simul- 

 taneous actions, some of which are very obscure ; the physical 

 mechanism implied in the process is subtle and mysterious, 

 the experimental observations are difficult to reconcile among 

 themselves, and there is no theory to adequately account for 

 the phenomena. It is not proposed, here, to make any attempt 

 at solving the difficulties, but rather to present them in the 

 form of experimental results. 



Celluloid. 



The first substance to be dealt with, in this regard, is 

 u celluloid." As far as can be judged by inspection it 

 appears to be a compound of guncotton and camphor, with a 

 trace of lime — possibly in the form of sulphate. When seen 

 through the microscope, small white spots become visible in 

 a translucent yellowish substance. In texture " celluloid " 

 resembles " cordite/' but it is of lighter colour, inflammable 

 but not explosive. The insulation of this substance was, at 

 first, measured in the following way : — A thin circular sheet 

 of celluloid was placed between two plane surfaces of brass 

 11 inches in diameter. A margin of celluloid was allowed, to 

 prevent leakage over the edges ; and a heavy weight was put 

 upon the top plate. When this sheet was submitted to the 

 action of a current, there was no such apparent increase of 

 resistance as is usually to be observed with dielectrics. The 

 galvanometer, in fact, indicated the reverse effect — the de- 

 flexion gradually increasing with time. No actual fault could 

 be detected in any of the samples, and yet the a electrification " 

 was negative. This curious effect was the more to be noticed 

 as the voltage of the testing-battery was increased. The 

 actual insulation resistance, calculated for the same sample, 

 with this apparatus, under various currents, showed that the 

 resistance changed enormously with the testing voltage. 

 In this case, and in all experiments here mentioned, the 



