695 



capacity (i.e. injurious) tliere will be wanted near the unstable state 

 of charge a very slight increase of charge for the variation in the 

 course of the lines of force between a and b considered by them- 

 selves; consequenlly for the motion of the needle; yet at the same 

 time the needle d will yet require much chai-ge for itself ; or : though 

 the useful capacity strongly increases in the unstable state, yet the 

 injurious capacity must be sei'iously taken into account. This diaw- 

 back makes itself felt especially when that injurious capacity in the 

 system undergoes the influence of the unstability as well as the 

 useful capacity. If it is supposed e.g. that a consists of a horizontal 

 disc, then part of the capacity of b will relate to lines of 

 force going from h to the horizontal plane of a (i.e. injurious 

 capacity). Also these Hues of force will then undergo a change 

 in consequence of the movemenf : that is to say, that also this 

 injurious capacity vvill constantly increase while passing to 

 higher states of charge, which in itself is disadvantageous. From 

 this consideration it follows that the advantage of unstability is still 

 bound up with another condition ; the optimum is implied in the 

 following, rule : the greatest sensibilit}' of charge in a system will be 

 obtained by a maximal approximation to the unstable state; at the 

 same time the amount of the injurious capacity will have to be as small 

 as possible and by no means to undergo the influence of unstability. 



As regards fui-ther the capacity of the whole system together, 

 peculiar relations may crop u[) in the case of change of the latter. 

 We have noticed already that with a positive increase of charge the 

 induced charge, which is dis|tlaced by the movement of the needle 

 arrests the increase of potential in the system. Thus it may occur 

 that the increase of potential is compensated by that very influence, 

 i.e. the system would then possess an infinitely great capacity ; this 

 will occur among others when the injurious capacity of the system 

 possesses a small amount of capacity. If one passes on to higher 

 states of charge then a positive increase of charge will even bring 

 about a decrease of potential i.e. a negative capacity for the system. 



As to the electrometer described here, I think I have obtained 

 favourable results in relation to the consideration given here. Ex- 

 periments are arranged for in order to become more acquainted 

 yet with the ratio of useful to injurious capacity in the various 

 states of charge in this system, which cannot yet however, be con- 

 sidered as being put an end to ; also about the influence of the 

 thickness of the suspension wire and modification in the shape of 

 the needle a closer investigation is still in preparation. 



Physical Laboratory of the University of Groningen {Holland), 



50* 



