460 Proceedings of the Royal Society of Edinburgh. [Sess. 
XXXII. — Observations of the Earth-air Electric Current and the 
Atmospheric Potential Gradient at Edinburgh. By G. A. 
Carse, D.Sc., and D. MacOwan. 
(Read January 10, 1910. MS. received May 31, 1910.) 
The portable gold-leaf electrometer designed by C. T. R. Wilson * gives a 
means of measuring the charge upon and current through a conductor 
exposed to the earth’s field and maintained at zero potential. Further, 
Wilson j* has shown (1) that the dissipation factor (the ratio of current per 
minute to the corresponding charge) is approximately the same for a 
surface of turf and the metal test-plate ; and (2) how to deduce the corre- 
sponding charge and current per square centimetre on the neighbouring 
ground-level. Wilson’s measurements were made chiefly in a country 
atmosphere (near Peebles), and we have made observations with a similar 
instrument in town air, in and near Edinburgh, to find out whether the 
dissipation factor is notably affected by the purity of the atmosphere as 
regards smoke, etc. 
Apparatus and Method. 
For a full description of the electrometer and the method of using it, 
the reader is referred to Wilson’s papers ( loc . cit.). The gold leaf, which 
hangs within an inner case, kept at a constant potential by means of a 
quartz Leyden jar, has connected with it, by a vertical metal rod, a hori- 
zontal circular brass plate, the test-plate, 6*95 cms. in diameter, and this 
* Proc. Garnb. Phil Soc., xiii., 4, 184, 1905 ; ibid., xiii., 6, 363, 1906. 
+ Proc. Roy. Soc., A, Ixxx., 537, 1908. 
