[WRIGHT] VARIATIONS IN THE CONDUCTIVITY OF AIR 



TABLE I. 



87 



II. — Apparatus. 



Measurements such as were contemplated on the ionization in metal 

 I'eceivers over the surface of the lake required the use of some instru- 

 ment which would be portable and at the same time not easily put 

 out of adjustment. The electroscope recently devised by C. T. B. 

 Wilson was found to fulfil all the requirements. 



The instrument, Fig. 1, consisted essentially of a gold leaf sys- 

 tem 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. 



In making a measurement on the conductivity of the air with this 

 instrument, the metal receiver was placed on top of the electroscope, as 



'Eve., Phil. Mag., Sept., 1906. 



^'H. L. Cooke, Phil. Mag, p. 403, 1903. 



"McLennan, Phil. Mag., Dec, 1907. 



