Section III., 1911. [23] Trans. R. S. C. 
Measurements of Precision on the Penetrating Radiation from the Earth*. 
By ARTHUR Tromson, M.A. 
Presented by Pro‘essor J. C. MeLennan. 
Read May 16, 1911. 
(Abstract.) 
In this paper an account was given of an installation of apparatus 
designed to make measurements of precision on the intensity of the pene- 
trating radiation from the earth. The ionizing chamber consisted of a 
galvanized ion receiver of about 300 litres capacity. It was installed 
on the roof of the Physical Laboratory at Toronto and was well exposed 
to the penetrating radiation in free space. 
The arrangement is shewn in Fig. I. The Electrode B was of 
special form as shewn in the diagram. The rod C attached to the re- 
ceiver gave such a configuration to the applied electric field as to in- 
sure the collection of ions from the space enclosed by the bars of the 
electrode as well as from the space between these bars and the walls 
of the receiver. 
Before being placed in position the receiver was carefully tested 
and found to be absolutely air-tight. The measuring instrument was 
a quadrant electrometer installed in a room in the laboratory directly 
below the receiver. All electrical connections between the receiver 
and the measuring apparatus were carefully protected by well earthed 
metallic screens. 
In making the readings a potential of 160 volts was maintained on 
the receiver, and as the ionization curve in Fig. II. shews this was ample 
to insure saturation. 
A self recording piece of apparatus has been constructed which 
will take readings every 10 minutes over a period of eight days. With 
this arrangement it is proposed to take consecutive readings without 
interruption over long continued periods of time. In this way it is 
expected that very exact information will be obtained on possible 
variations in the intensity of the radiation. Such variations Wright* 
and Clinef have shewn must be small at Toronto. 
After installing the apparatus and before proceeding with the self- 
recording observations a series of sets of measurements was made visu- 
* Wright, Phil. Mag. Feb. 1909. 
7 Cline, Bulletin Roy. Soc. of Canada, Oct. 1909. 
