296 Cooksey — Corpuscular Rays produced in 



velocity, and leads us to believe, as mentioned above, that we 

 are dealing with corpuscular secondary rays of velocities com- 

 parable with those measured by Seitz. 



In subtracting the secondary Rontgen rays, where the points 

 lie badly off the curve, the curve was taken in preference to 

 the point. Attention should be called to the points for zinc 

 and copper corresponding to the intensity of the rays after pass- 

 ing through four sheets of aluminium. These points lie as 

 high or higher than the corresponding ones for three sheets, 

 and it is due in all probability to an error in measuring the 

 thickness of the fourth sheet of aluminium. A different sheet 

 was used for the other metals, but I have not had time to repeat 

 the two curves in question. 



An attempt was made to see if the absorption of the corpuscular 

 rays followed an exponential law. To this end the common 

 logarithms of the points (given in columns III and III' of the 

 tables) were plotted. The origin was taken at the point on the 

 axis of ordinates corresponding to unit intensity of the second- 

 ary rays, and the logarithms of the intensity plotted down, 

 each tenth division for the intensity being equal to two tenths 

 for the logarithms. The values of the logarithms are given 

 in columns IV and IV of the tables. 



For the more penetrating primary rays the points all lie 

 pretty well on the straight line passing through the origin. 

 This would seem to show that the corpuscular secondary rays 

 produced by hard primary rays were very homogeneous in regard 

 to velocities and were absorbed according to an exponential 

 law. When we come to consider the soft rays we find that if 

 we neglect the origin, the points lie fairly well on a straight 

 line which cuts the axis of ordinates below the origin. This in 

 connection with the absorption curves for the corpuscular rays 

 leads us to the conclusion that the soft primary rays give rise 

 to corpuscular rays between 70 per cent and 80 per cent of 

 which are slow moving corpuscles which are almost all absorbed 

 in the first -001 mm of aluminium, and the rest faster moving 

 corpuscles which are absorbed according to an exponential law ; 

 but in all cases, except nickel and copper, these corpuscles are 

 slower moving than those produced by the hard primary rays. 

 These exceptions, I am inclined to think, are again due to not 

 taking sufficient account of the secondary Rontgen rays present.* 



In the case of tin and silver the points for the rays produced 

 by the soft primary rays lie on a straight line passing through 

 the origin, showing that the corpuscular rays from these metals 

 are very homogeneous even though produced by soft primary 

 rays. 



* The writer hopes to investigate this question further by using a shorter 

 ionization chamber. 



