SPECIFIC INDUCTIVE CAPACITY 



125 



on the sulphur sphere gave the following values of K parallel to 

 the three axes. The values of p 2 along the axes as assigned by 

 Boltzmann are also given. 



I 



k-778 

 3-970 

 3-811 



4-596 

 3-886 

 3-591 



Hopkinson's experiments. Hopkinson * made an exten- 

 sive sen* arches on the specific inductive capacities of solids 

 and liquid*. u>ing for exact measurement a parallel plate con- 

 dcn>er in which the distance between the plates could be varied till 

 the capacity was equal to that of another condenser. The principle 

 of the method may be gathered from the diagrammatic repre- 

 sentation in Fig. 85. 



Let B be a battery of cells earthed at its middle point, so that 

 the potential of one terminal is as far above that of the earth as the 



K 



f/i 



Fio. 85. 



potential of the other terminal is below it. Let C be the variable 



condenser with parallel adjustable plates, and let S be the con- 



-er with which it mu*t be equalised, in practice a sliding 



of two co-axial cylinders. Q is a quadrant 



electrometer. Ix-t the lower plate of C and the outer cylinder 



of S be I the upper plate of C and the 



inner cylinder of S r -pectively with the -f and terminals of 



tin li.-itt. iv hy means of the k( -\N K, K t . Then move K x and K 2 



he tuo condenser! are connected together and to the 



met r. If the capacities are equal the two charges 



are equal and opposite, and will neutralise each other, but if 



.-in excess of one kind of charge indicated by the electro- 



Original Papert, vol. ii. p. 54. 



