428 Royal Society. 



The fact that water acquires greater power of electrolytic induc- 

 tion by the addition of sulphuric acid, which not being itself decom- 

 posed, can act only by giving increased facihty of conduction, is ad- 

 duced as confirming the views of the author. 



The phenomena of the disruptive electric discharge are next ex- 

 amined with reference to this theory : the series of inductive actions 

 which invariably precede it are minutely investigated : and reference 

 is made to the accurate results obtained by Mr. Harris, as to the law 

 of relation between the intensity of a charge, and the distance at 

 which a discharge takes place through the air. 



The theory of Biot and others, which ascribes the retention of a 

 charge of electricity in an insulated body to the pressure of the sur- 

 rounding atmosphere, is shown to be inconsistent with various phe- 

 nomena, which are readily explained by the theory adopted by the 

 author. 



The author then enters into an inquiry relative to the specific con- 

 ducting capacities of different dielectrics. 



With a view of determining the degrees of resistance to the transit 

 of electricity excited by different kinds of gases, he constructed an 

 apparatus, in which an electric discharge could be made along either 

 of two separate channels ; the one passing through a receiver filled 

 with the gas, which was to be the subject of experiment, and the 

 other having atmospheric air interposed. By varying the length of 

 the passage through the latter, until it was found that the discharge 

 occurred with equal facility through either channel, a measure was 

 afforded of the relative resistances in those two lines of transit, and 

 a determination consequently obtained of the specific insulating 

 power of the gas employed. 



The circumstances attending the diversified forms of the disruptive 

 discharge, such as the vivid flash or spark, the brush or pencil of 

 light, and the lucid point or star, which severally represent different 

 conditions of the sudden transit of electrical forces through an inter- 

 vening dielectric, are minutely investigated in their various modifi- 

 cations. The spark is the discharge, or reduction of the polarized 

 inductive state of many dielectric particles, by the particular action 

 of a few of those particles occupying but a small and limited space, 

 leaving the others to return to their original or normal condition in 

 the inverse order in which they had become polarized : and its path 

 is determined by the superior tension which certain particles have ac- 

 quired, compared with others, and along which the action is accord- 

 ingly conducted in preference to other lines of transit. The variety 

 in the appearance of the electric spark taken in different gases may 

 be ascribed partly to different degrees of heat evolved, but chiefly to 

 specific properties of the gas itself with relation to the electric forces. 

 These properties appear also to give occasion to diversities in the 

 form of the pencU or brush, which takes place when the discharge 

 is incomplete, and is repeated at short intervals, according to the 

 shape of the conductor on either side, and according to the species 

 of electricity conveyed. The diverging, converging, bent and rami- 

 fied lines presented in these different forms of electric discharge. 



