B93 



pai't which inflnences the motion of a; by injurious capacity that par^ that 

 lacks this influence and therefore means only disadvantage here. As 

 to the measurements, the sensibility will rise together with the increased 

 states of charge. In order to bring this out, we have to compare e.g. the 

 measurements of the two following states : State 1 : (-|- 8, 0, — 4) Volt 

 and state II : (-)- 14, 0, — 6) Volt, and suppose h to be insulated, so that a 

 supposed ionisation current gives a positive charge to the lower needle 

 b -\- d {/ at -{- 80 Volt e.q.). What then will be the effect with in both 

 cases a definite equal increase of charge? The potential value of b 

 will rise, the number of lines of force between a and b decrease 

 at the same time so that the upper needle recedes from the lower. 

 In consequence of the fact that a, which is positively charged, recedes 

 from b, part of the negative charge induced on b by a in the state 

 of equilibrium, will be set free and therefore will be spread over 

 the now insulated system b -j- d- The influence of this will, first of 

 all, consist in a decrease of potential of 6, causing the potential 

 value of /; to increase less than would follow from the addition of 

 charge considered by itself (ionisationcuri-ent). This influence is felt 

 strongest in the case of II, where in consequence of greater potential 

 difference between a and 6, a greater quantity of induced charge is 

 set free, so that the potential decrease, caused by this will be greater. 

 But from yet another point of view we shall have to look at the 

 part played by the induced charge: as soon as the latter spreads 

 from b over b -\- d, this in itself means again a decrease of lines of 

 force between a and b, i.e. a cause of motion on the needle. The 

 result of this consideration therefore is that the displacement of the 

 upper needle a will only partly be the consequence of a direct 

 addition of cliaige from the ionisation current, but at the same time 

 must be partly considered as the consequence of/ the displacement of 

 induced charge in the system. 



Where, therefore, this displacement is greatest i.e. in case II, the 

 motion on the needle will be strongest and consequently the sensi- 

 bility of charge greatest. 



In communication 1 the above mentioned explanation has been 

 worded somewhat differently ; it was namely said there, that the 

 greater sensibility in II would be the consequence of the fact that 

 the increase of the capacity of b -\- d would especially mean increase 

 of useful capacity in the system, by which the sensibility of charge 

 will increase. In order to elucidate this more clearly, 1 shall return 

 to what was communicated above; that, )iamely, by displacement 

 of induced charge, owing to the motion of a, the rise in potential 

 of b turns out smaller than might follow from the addition of charge 



50 



Proceedings Royal Acad. Amsterdam. Vol. XX. 



