Section III., 1913. [27] Trans. R.S.C. 



Measurements on the Earth's Penetrating Radiation with a Wulf 



Electrometer.'^ 



By Professor J. C. McLennan and Mr. A. R. McLeod, 

 University of Toronto. 



(1) Introduction. 



In a paper by one of us in the Phil. Mag., of Sept., 1912, the results 

 were given of a number of observations on the intensity of the earth's 

 penetrating radiation taken with a C.T.R. Wilson gold leaf compensating 

 electrometer, at a number of points on the sea and also at a number of 

 places on land on both sides of the Atlantic. These results shewed that 

 while at a number of places in England and in Scotland and in the open 

 at and near Toronto the number of ions generated per cc. per sec. in a 

 zinc vessel containing air and hermetically sealed was between eight 

 and nine, the number generated in the same vessel on a steamer on the 

 Atlantic was only about 6-03 ions per cc. per sec. 



The readings on the Atlantic were taken with difficulty on account 

 of the continued oscillation impressed upon the gold leaf system by the 

 swaying of the steamer. As a result these readings were not considered 

 to have the same reliability as those taken on land at the different points 

 of observation. 



With a view to obtaining more reliable observations on the sur- 

 face of the ocean a set of readings was taken when crossing the 

 Atlantic in September, 1912, and again a third one when crossing in 

 June of the present year. This time, however, a Wulf bifilar electro- 

 meter was used. The instrument behaved admirably and with it read- 

 ings were taken on board ship with the same ease as on land. 



II. Apparatus and theory of instrument. 



The form of the instrument used is shewn in Fig. I. It consists 

 of a cylindrical receiver of zinc provided with plane sides which had a 

 capacity of about two litres. The electrical system consisted of two 

 conducting fused quartz fibres attached at their upper ends to an insu- 

 lating support and at th'eir lower ends to a cross fibre also of fused quartz 

 under tension. This cross fibre was attached to an insulating support 

 as shewn in the figure. The instrument was provided with a metal 

 *Read before the Royal Society of Canada, May 28th, 1913. There are also 

 inserted in the paper some observations on the intensity of the penetration radia- 

 tion made during a voyage across the Atlantic in June, 1913, together with some 

 comments upon these observations. 



