665 



lo tliG value of tfie capacity, it does by no means follow froni this 

 that the sensibility of charge will be greatest for a capacity as small as 

 possible, and a potential sensibility as great as possible ; for the latter 

 quantities are not independent of each other, as appears clearly among 

 others in what was said under 2. therefore I cannot entirely concur 

 with Labordk's statement, in his : "Methodes de mesure, employees 

 en radioactivité, page 66", where he says : "I'appareil le plus sensible 

 aura une grande sensibililé aux Volts et nne faible capacité" ; in 

 this statement the above mentioned relation is namely not taken 

 into account. 



Thus in consequence of the existing mutual dependence of capacity 

 and potential sensibility it will be possible — and it will be shown 

 here that this really applies to the discussed electrometer — that 

 it will be favourable for the sensibility of charge, to take the capacity 

 not as slight as possible, when namely an accompanying increasing 

 potential sensibility more than compensates the disadvantage of 

 this procedure. 



That this case presents itself in the described apparatus may be 

 shown by first examining of what the capacity of the apparatus, i.e. 

 of the needle h-\-d really consists. This capacity consists of : capacity 

 of the part h, which refers to arising or vanishing lines of force 

 leading to a or c, and capacity of d. 



Now 1 would distinguish in this capacity between : 



a. useful capacity, by which I mean capacity which has an influence 

 on the motion of a\ 



b. injurious capacity which lacks this influence, and which is really 

 a disadvantage here, because it binds charge of the ionisation 

 current without making it demonstrable* Of the above mentioned 

 capacity only that corresponding to the lines of force between a and b 

 is certainly almost entirely useful capacity (see below); the rest is 

 injurious. 



And in this lies the cause why the state with greater potential 

 difference between a and b, though attended with greater capacity, 

 can yet mean greater sensibility of charge; for this increase of capacity 

 concerns here the capacity of b with respect to a; this is increased, 

 (according to 2) hence the useful capacity of b is increased; the 

 greater now the ratio of useful to injurious capacity is, the greater 

 the sensibility of charge. 



For the rest, as regards the value of the injurious capacity in the 

 apparatus, the following remarks may be made: 



1. The injurious capacity of d with resj)ect to ƒ will not be of 

 great influence, since the distance to / is great. 



44* 



