respecting Electrical Influence. 457 



the following rule can be laid down : — Those bodies which 

 during both charges are either in conducting communication 

 with the earth, or insulated and initially unelectric, and in 

 being charged receive no electricity, may be left out of consi- 

 deration in constructing equation (I.). 



It may now, as a special case, be assumed that with all the 

 given bodies, with the exception of C^ and C2, one of the two 

 conditions mentioned occurs. The equation then reduces to 



YiOi + y2 02=iSiOi + 552Q2 (5) 



If this equation be still further simplified by making special 

 assumptions respecting the behaviour of the bodies Ci and C2, 

 we arrive at the reciprocity-theorems mentioned at the com- 

 mencement. 



We will first suppose the two bodies insulated and initially 

 unelectric, and assume that in the first charging the body Ci 

 only acquires the quantity of electricity E, by the influence 

 of w^hich the potential-level y2 is produced in C2, and that in 

 the second charging only the body C2 receives the quantity of 

 electricity E, through the influence of which the potential- 

 level ^1 arises in Ci- In this case we have to put 



Q2 = Oi = 0, Qi = 02 = E, 



by which (5) is changed into 



V2E=35iE, 

 or 



V2=S5i (6) 



Consequently the potential-level which arises in C2 through 

 Ci being charged with a certain amount of electricity, and 

 that which arises in Ci through C2 being charged with the 

 same amount, are equal to one another. 



We will make the further assumption, that in the first 

 charging Ci is charged up to the potential-level K, while C2 

 is connected to earth and through influence receives from the 

 earth, the amount of electricity Q2, and that in the second 

 charging C2 is charged up to the potential-level K, while Cj is 

 connected to earth and through influence receives the amount 

 Oj of electricity. We have then to put 



whereby (5) is changed into 



KDi=KQ2, 

 or 



Oi=Q2. ....... (7) 



Consequently the amount of electricity which through influ- 



