482 MEASUREMENT OF CAPACITY. DIELECTRICS. 



it is ascertained whether the potential of the Leyden jar has the 

 same value in successive experiments. If the movable ball is formed 

 alternately of a dielectric and of a conductor, the ratio of the de- 

 flections is equal to the ratio of the corresponding attractions. 

 There are, however, small corrections to be made which arise either 

 from the difference of volume of the balls or from the change of 

 distance produced by unequal attractions. 



As the actions observed are always attractive, whatever be the 

 electrical condition of the Leyden jar, the experiment may be 

 repeated several times by successively charging and discharging 

 by hand, or even by altering the signs by the action of a plate 

 which vibrates between the armatures of two batteries electrified 

 in contrary directions. In this way we determine the influence 

 of the time of charge on the specific inductive capacity. 



In experiments of attraction the phenomenon depends on the 

 entire mass of the body electrified by induction, and not merely 

 on the surface, as with conductors. This has been directly verified 

 by Romich and Fajdiga* with balls of sulphur covered with paraffine, 

 or of shellac. 



1072. The method has the particular advantage of only re- 

 quiring a very small quantity of the body under experiment, and 

 of being applicable to crystallised bodies. 



Electrification by induction follows the same laws as magnetisa- 

 tion by induction, the intensity of magnetisation being equivalent 

 to intensity of electrification that is to say, to the electrical moment 

 K(/> (178) of unit volume. In like manner for anisotropic bodies 

 (391), the electrical condition is the superposition of three con- 

 ditions which would be produced separately by the three components 

 of the electrical field parallel to the principal axis of elasticity. 



By measuring the attraction exerted between spheres of crystal- 

 lized sulphur, parallel to the three principal axes, Professor Boltzmannf 

 obtained three very different values for the specific inductive capacity 



'970 



MM. Romich and Nowak{ have applied the same method to several 



* ROMICH and FAJDIGA. Wiener Sitz. Berichte, Vol. LXX., Pt. ii., p. 367. 1874. 



f BOLTZMANN. Wiener Sitz. Berichte, Vol. LXX., Pt. ii., p. 342. 1874. 



I ROMICH and NOWAK. Wiener Sitz. Berichte, Vol. LXX., Pt. ii., p. 380. 1874. 



