from a Plate exposed to Rays from Radium. 

 Table II. 



181 



Thickness 



of screen S 



in mm. 



0-000 

 0-020 

 0-225 

 1-00 

 1-80 

 110 



Thickness of plate A. 



o-oo 



15-4 mm. 



Differ- 

 ence. 



Giving the leak when air is 

 exposed to 



fi + y rays. 



y rays. 



(3 rays. 



12-50 



1-89 



10-6 



3-94 



1-91 



2-03 



2-00 



1-94 



•06 



1-97 



1-96 



•01 



1-95 



1-95 



•00 



1-93 



1-92 



•01 



Thickness of plate A. j*.™ 



o-oo 



15-4 



Giving the leak when plate 

 R 1*8 mm. thick is exposed to 



/3 + y rays. 



y rays. 



104-2 



2-85 



51-4 



2-38 



5-59 



2-02 



2-15 



1-98 



2*02 



1-96 



2-00 



1-94 



/3 rays. 



101-3 

 520 

 3-57 

 •17 

 •06 



In these observations both @ and y rays were present to 

 affect the air, and in order to determine whether both soft 

 and penetrating rays were produced by both j3 and y rays, 

 another set of observations was taken with the y rays only 

 failing upon the air. To be perfectly certain that no /3 rays 

 would be present the cone C of 11*8 mm. of lead was put in 

 the opening, and for fear the chance of its not fitting exactly 

 might allow some stray /3 rays to emerge, a plate of 3*6 mm. 

 of lead was put at A. The total, 15'4 mm., is more than 

 enough to ensure the passage of nothing but y rays. The 

 results are given in the third column, and the differences of 

 the second and third columns will show the leaks due only to 

 the/3 rays ; these are found in the fourth column. It will be 

 seen that the radiations set up in air by /3 rays are practically 

 all of the soft kind and are absorbed by 1 mm. of lead. 



To return to the observations on the effects of the y rays, 

 as given in column 3, which are of considerable interest. 

 The numbers are at first sight rather surprising and anomalous. 

 With no screen the rate of leak is 1*89 ; when a screen S is 

 put in the path of the rays we expect a reduction of the leak 

 due to absorption of the radiation by the screen; but we 

 find that a layer of ^mm. thickness increases the leak to 

 1*91, and that the leak increases with increasing thickness of 

 screen, until for 1 mm. the leak is 1*96, nearly 4 per cent, 

 greater than with no screen. For still greater thickness of 

 screen the leak decreases again, but even after a plate 



