h>i tlw Mot 



(Oil of 



l\miiri' 1 



oiis ni (C 



Ga.^ 



603 



served to connect the aj)[)aratiis with ii Toe|»ler-j)inn|) and a 

 MacLeod gaiioe. For the jjurpose of adjiistin*;- the pressure 

 (which can he done only roughly hy means of the i-uunp) the 

 apparatus was connected to the top of a glass bulb provided 

 with a barometric tube leading to a mercury reservoir by 

 tlexible tul)ing in the ordinary manner. It was then possible 

 to adjust the pressure of the gas in the apparatus to any 

 required value b}^ altering the height of the reservoir. 



In order to tind the conductivities betw^een the plates it 

 was found very convenient to use an induction-balance. 

 The currents cannot be measured conveniently by the ordi- 

 nary method of electrometer deflexions since the quantities 

 vary over such a large range, and when this method is used 

 it is necessary to make a correction for the capacity of the 

 j)late B, which varies with the distance between the plates. 



The arrangement of the apparatus which was used for 

 measuring the quantities of electricity acquired by the 

 plate B is shown in fig. 2. A parallel plate condenser 



Fie 



having seven plates was set up in a brass case which was 

 maintained at zero potential. The plates Ci, Co, c^ were care- 

 fully insulated from the other plates, and a short connector 

 from each plate terminated in an insulated mercury cup out- 

 side the case. The four other plates d were connected 

 together and insulated from the case. When the plates d 



