298 



Mr. C. S. Wright on Variations in the 



2. Apparatus. 



Measurements such as were contemplated on the ionization 

 in metal receivers over the surface of the lake required the 

 use of some instrument which would be portable, and at the 

 same time not easily put out of adjustment. The electro- 

 scope recently devised by 0. T. R. Wilson was found to 

 fulfil all the requirements. 



The instrument, fig. 1 and fig. la (PL IV.), consisted essen- 

 tially of a golf-leaf system G, insulated from the outer case by 

 a quartz ring and suspended inside a similarly insulated inner 

 case connected with a quartz leyden-jar of about 100 cms. 

 capacity charged to a potential of + 50 volts. 



Fig. 1. 



L 



In making a measurement on the conductivity of the air 

 with this instrument, the metal receiver was placed on top 

 of the electroscope as shown in fig. 1, and supported on 

 ebonite blocks so as not to be in electrical connexion with 

 the instrument proper. The receiver was then charged to 

 any desired voltage, and the current through the air observed 

 by the charge which was communicated in a given time to 

 the electrode carried by the gold-leaf system. 



The function of the compensator C, which consisted of a 

 sliding tube-condenser, was to annul by its motion any charge 



