+ THE ROYAL SOCIETY OF CANADA 
(4). That in some localities marked daily variations occur in the 
intensity of the penetrating radiation while in others no indications of 
such variations have been found. 
(5). That the ionisation produced in the air in metallic receivers 
by the penetrating radiation together with the rays from the walls of 
the vessel and by other unknown contributory agents varies according 
to different observers from 3-5 to over 30 ions per cc. per second. 
From this summary it will be seen that there is a marked lack of 
agreement on two very important points; eg. Is there a diminution 
in the intensity of the penetrating radiation with increasing altitude or 
not? And are the periodic variations in the ionisation noted by some 
observers due to variations in the intensity of the penetrating radiation 
or are they due to other influences which have not been eliminated in 
the conditions of measurement? 
One of the best ways of answering these questions would be for 
the same observer with the same instrument to make measurements 
at points for which we have results which do not agree and measure- 
ments such as those recently made by Simpson and Wright! on the 
Terra Nova and at points of call on their voyage to the South Pole, 
which are of that character, will do much to clear up some of the obscure 
outstanding points in connection with the anomalous results on record 
from measurements on this type of radiation. 
II.—Observations on the Penetrating Radiation in Different Localities. 
Some measurements made by the writer during a recent stay in 
Great Britain and during the voyage following to Canada, also throw 
some light on the questions raised above. 
In these measurements the arrangement of apparatus used was the 
one adopted by the writer and by Wright? and Cline® on different oc- 
casions at Toronto. It is shown in Fig. 1. The measuring apparatus 
was the well known C. T. R. Wilson compensating condenser gold leaf 
electrometer. The receiver R which had a capacity of about 30 litres 
was made of a sample of zinc about -5 mm. in thickness which on com- 
parison with a number of different samples was found to contain the 
least amount of radioactive impurities. The electrode E was provided 
with an earthed guard tube at I where it entered the receiver. 
Extreme care was taken before commencing the measurements 
to have the receiver R hermetically sealed so that there could be no 
——— 


! Simpson and Wright. Proc. Roy. Soc. Ser. A, Vol, 85, p. 175, 1911. 
? Wright Phil. Mag. 17, 1909. 
3 Cline Phys. Rev. 30, 1910. 
