the Eartlis Penetrating Radiation on Land and Sea. 521 



localities by different observers using a variety of measuring 

 instruments. 



In these measurements the intensity of the radiation was 

 generally found by determining the ionization produced by 

 it in the air confined in a metallic receiver. In some of 

 these determinations care was taken to have the metallic 

 receiver air-tight, but in a number of them this precaution 

 was not taken, either through its being considered un- 

 necessary or for other reasons. 



From the results of these measurements it would appear : — 



(1) That the soil and recks of the earth contribute by far 

 the greater proportion of the radiation. 



(2) That the intensity of the radiation is less over such 

 bodies of water as Lake Ontario, the Swiss Lakes, the 

 Southern Atlantic, and the Indian Ocean, than it is 

 over land lying contiguous to these waters. 



(3) That the intensity of the radiation when measured at 

 different levels above the ground in the neighbourhood 

 of Braunschweig *, and on such structures as the 

 Eiffel Tower f and the City Hall Tower % at Toronto, 

 decreases with the altitude of the point of observation, 

 but when measured from the basket of a gas-balloon 

 at a height of over 1000 metres above Vienna §, is 

 practically the same as it is at the surface of the earth 

 in that locality. 



(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 ionization 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 c.c. 

 per second. 



From this summary it will be seen that there is a marked 

 lack of agreement in regard to (i.) the diminution of intensity 

 with altitude, and (ii.) the daily variations in intensity. Two 

 questions still open are : — Is there a diminution in the 

 intensity of the penetrating radiation with increasing altitude 

 or not, and are the periodic variations in the ionization noted 

 by some observers due to variations in the iu tensity of 



* Bergwitz, Habilit-Sclirift Braunschiueig, 1910. 

 t Wulf, Phys. Zeit. xi. p. 811 (1910). 

 X McLennan & Macallum, Phil. Mag., Oct. 1911. 

 § Hess, Phys. Zeit. xii. p. 998 (1911). 



