ANIMAL AND VEGETABLE 98 



of overground wires, underground wires and cables ; and 

 one of the principal functions of a condenser, or of a series 

 of condensers, is in telegraphy to compensate for and 

 regulate this inequality of distribution. In the human 

 body, whose circuits are infinitely more com- 

 plex than the most complicated telegraph 

 system, they are not only designed for the 

 performance of this function, but for the 

 equally important one of changing the sign of Fig. 4. 

 current from efferent to afferent, or vice versa. 



" A simple condenser is, as we have seen, shown in Fig. 4. 

 If we connect that to a galvanic cell (Fig. 5) the charge 

 communicated to plate A will (if the plates 

 -^T I I ^ are of the same area) induce a charge of 

 p^v equal tension but of opposite sign upon 

 I I J plate B. 



j ,/ "The capacity varies directly as the 

 i surfaces of the opposing plates. If, now, 



three condensers F lf F 2 , F 3 , be joined up 

 as shown by Fig. 6, the effect is clearly to connect 

 all the A plates together, so that, practically, they become 



one plate of large area, and so also with the B plates ; 

 hence, by such an arrangement, the total capacity (F) 

 becomes 



F = F! + F 2 + F 3 



and the condensers are said to be connected in parallel. 



" Again, the capacity varies inversely as the distance 

 between the plates. Assume the distances in the following 



