M. B. W. Feddersen on the Electric Spark. 515 



by both. Concerning the value of a single partial discharge, 

 that is, the relation between the electricity eliminated by it to 

 the original charge, it is clear that such relation depends wholly 

 upon the quantity of electricity concentrated upon the polar 

 spheres (or upon one of them when the othjer is connected with 

 the earth), if the statical electricity upon the thin connector of 

 the great-resistance column may be neglected. Let us therefore 

 consider the polar substance in connexion with the internal 

 jar-coating. The irregular form of the body forbids the employ- 

 ment of calculation here; but by a simple course of reasoning, 

 we may explain the nature of the changes ; i. e. whether at the 

 moment before the discharge, the quantity of electricity con- 

 centrated upon the polar substance increases proportionally to 

 the charge, or more quickly, or more slowly; and the solution 

 of this question is for the present sufficient. 



It is, namely, evident that, without the induced action of the 

 polar body in connexion with the earth, the second pole, which, 

 with the internal coating, forms a continuous, invariable whole, 

 always has upon its surface a definite aliquot part of the entire 

 charge. This is also evidently approximately true if the first- 

 named connected polar body be considered as present, but at a 

 sufficient distance (at a great distance of discharge). If, now, 

 the distant pole be brought nearer, on the one hand the free 

 electricity upon the pole in connexion with the internal coating 

 would remain the same with respect to the entire charge, on the 

 other hand a certain quantity of fixed electricity* would be 

 withdrawn from the reservoir, in consequence of the inducing 

 action of the earth-connected pole. Such abstraction would 

 always increase as the distance diminished. The entire elec- 

 tricity upon the pole (whose unit of quantity is always given 

 by the corresponding charge) is therefore the sum of a con- 

 stant and a variable, the latter of which increases as the distance 

 of discharge increases. Hence, on increasing the total charge, 

 the value of a partial discharge is not increased to the same 

 extentf. 



Accordingly, if -j- were conditioned wholly or principally by 



the value of the partial discharge, its change could only take 

 place in the opposite direction to that which is shown by ex- 



* The capacity of the reservoir is always assumed to be so great that 

 the loss of this electricity alters the density of the free electricity in the jar 

 inai)j)reciably. 



+ Perha])s the explanation gains in perspicuity by remembering that 

 not only the jar, l)ut also the system of the two polar bodies may be re- 

 ceived as an electrical condenser, witii the exception that in this case the 

 thickness of the isolating coating is variable. 

 2 I. ^ 



