ANIMAL AND VEGETABLE 81 



force and differences in the nature or chemical compo- 

 sition of the insulating substance. 



Even when in two condensers the conducting plates 

 are of equal surface- area, are equidistant, and E.M.F. is 

 constant, it does not follow that their capacity will be the 

 same. Suppose the dielectric of one to be paraffin and of 

 the other gutta-percha. The specific inductive capacity of 

 air being taken as 1, paraffin is 1-99 and gutta-percha 4-2. 

 It will, therefore, be seen that upon charging these two 

 condensers to the same potential difference the condenser 

 with the gutta-percha dielectric will receive a charge about 

 2-1 times greater than the condenser with the paraffin. 

 Moreover, capacity depends also upon the thickness of the 

 dielectric, in the inverse ratio. 



As regards a comparison of the capacity of the human 

 body with that of a submarine cable, the average capacity 

 of the latter ranges at about 0-3 microfarad per knot, 

 while I have found the former, using the same battery- 

 power, to be nearly 4 micros. Its absolute insulation 

 resistance is, however, comparatively low, and charge is not, 

 therefore, retained. 



I extract the following from one of my old note-books : 



" When the body was charged for fifteen seconds with 

 fifteen cells the immediate discharge (with 30 ohm shunt) 

 was 220 mm. Again charged for fifteen seconds and 

 insulated for sixty seconds, the discharge was 36 mm., and 

 upon this being repeated many times it became evident 

 that by reason of the low absolute insulation resistance of 

 the body the charge was given off to air in a short period 

 of time. As a result of this and another series of tests with 

 earth connections, I find that the body, when insulated, 

 does not act as a plate of a condenser as regards the earth, 

 but that the body itself acts in every respect as a condenser 

 of low insulation." But there is this to be said : the quan- 

 tity of the charge communicated to the plates depends directly 



G 



