354 Mr. C. A. Sadler on 



with either q l or q 2 . This will be the case if the number of 

 ions produced by a corpuscle before it ceases to act as an 

 ionizing agent be a comparatively large number. 



The fact * that the corpuscular radiation is absorbed by air 

 according to an exponential law would lead one to suppose 

 that the absorption of the corpuscles is due to their diffusion 

 by the air molecules, and not to any appreciable extent to a 

 diminution of velocity. 



One striking result which appears from an examination of 

 the figures given in Table V. is the following. 



With iron as tertiary radiator, a large increase in the value 

 of R occurs when the secondary radiation from nickel is used. 

 With copper as tertiary radiator, a large increase in the value 

 of R occurs when the secondary radiation from arsenic is 

 used ; with silver as tertiary radiator, a large increase in the 

 value of R occurs when the secondary radiation from tin is 

 used. These values are underlined in the table. 



These results are well indicated in fig. 9 (PL V.) where 

 the ordinates represent values of R while the abscissae are 

 the atomic weights of the secondary radiators. 



Now in each of these cases this large increase in the 

 emission of corpuscular radiation coincides with the corre- 

 sponding increase in the production of tertiary Rontgen 

 radiation characteristic of the tertiary radiator previously 

 mentioned in this paper f. 



It would appear then that some intimate connexion exists 

 between the production of Rontgen radiation in a substance 

 and the emission of corpuscular radiation by that substance. 

 The writer has not met with a single instance in which homo- 

 geneous Rontgen radiation characteristic of a substance is 

 produced without the simultaneous special emission of cor- 

 puscular radiation. But the converse is by no means proved. 

 For an examination of Table V. shows that a considerable 

 emission of corpuscular radiation from silver used as a tertiary 

 radiator occurs even when none of the homogeneous radiation 

 characteristic of silver is produced. For instance, when the 

 secondary exciting beam from silver itself falls upon silver 

 as tertiary radiator, no homogeneous Rontgen radiation is 

 produced, and yet a considerable emission of corpuscular 

 radiation occurs. 



But in the cases J where none of the homogeneous Rontgen 

 radiation characteristic of a metal is produced, a portion of 

 the exciting beam falling upon the metal is scattered. It is 



* i Conduction through Gases/ J. J. Thomson, p. 379. 



t Sadler, Phil. Mag. July 1909. 



\ Barkla and Sadler, Phil. Mag. Oct. 1908, pp. 550-584. 



