160 Mr Cooke, Experiments on Penetrating Radiation. 



Experiments on Penetrating Radiation. By H. L. Cooke, 

 1851 Exhibition Scholar of McGill University: Emmanuel 

 College. 



[Received May 1905.] 



In a previous paper* the author has shown by experiments 

 carried out at the McGill University, that the natural ionization 

 in a closed vessel is to be partly ascribed to a penetrating radia- 

 tion. Large masses of lead were used as screens to shield a brass 

 electroscope from this radiation, and a diminution in the ionization 

 of between 30 °/o an d 35 % was observed, the radiation inside the 

 laboratory being shown to come from all directions with equal 

 intensity. Experiments were also made to test the ionization 

 outside the laboratory, on the surface of the frozen ground, and 

 on the roof. The experiments showed the existence of a pene- 

 trating radiation under these altered conditions, but gave no indi- 

 cation as to its source or direction. The experimental arrangements 

 consisted of taking alternate runs, first with the vessel exposed, 

 and then surrounded on all sides by a lead cage, one inch in thick- 

 ness. A diminution in ionization was always observed, but the 

 amount of this reduction was not accurately determined, owing 

 to the difficulties of experimenting under the conditions en- 

 countered, and on account of the fact that the apparatus was not 

 well adapted for experiments involving great changes of tempera- 

 ture, which were sometimes as great as 30° C 



The primary object of the present research was to detect and 

 measure, if possible, any penetrating radiation coming from the 

 atmosphere. The existence of such a radiation is important from 

 the point of view of atmospheric ionization at high altitudes. 

 The radiation measured in the experiments at Montreal was such 

 that about one-third of an inch of lead screen reduced it to half 

 value, and its effect was not observable after passing through a 

 thickness of 2 inches of lead. This would mean that the effect 

 of this radiation from the earth would be inappreciable at a height 

 of 500 yards, and any ionization above this height would have to 

 be ascribed to radiations arising from the air itself or to radio- 

 active impurities mixed with it. 



In these experiments a small portable ionization vessel was 

 used, being designed to work independently of changes in tem- 

 perature and weather conditions, and capable of withstanding 

 comparatively rough handling, and being turned on its side and 

 inverted. The difficulties of designing such a vessel were con- 

 siderable, and the form of apparatus shown in the accompanying 



* Phil. Mag., Oct. 1903. 



