different Metals by Rimtgen Rays. 303 



parent to the primary rays in comparison to lead than nickel 

 is, follows the rule ; but a comparison of the absorption coeffi- 

 cients for the corpuscular rays will show that the corpuscles 

 from lead, due to soft primary rays, are nearly as penetrating as 

 those from nickel and much less penetrating than those from 

 zinc. This should easily account for the exception. 



Summary. 



The results from these experiments may be summarized as 

 follows : — 



1. The velocities found from the absorption in aluminium 

 of the corpuscular secondary rays produced when Rontgen 

 rays fall on heavy metals are in good agreement with the veloc- 

 ities found by other investigators, for all the metals considered. 



2. The more penetrating primary rays produce more pene- 

 trating corpuscular secondary rays. 



3. For the more penetrating primary rays used the corpus- 

 cular rays from all the metals tested, with the exception of 

 nickel, possessed nearly equal penetrating power ; while for 

 the less penetrating primary rays the penetration of the cor- 

 puscular rays varied, considerably for the different metals, those 

 from lead being the least penetrating. 



4. The corpuscular rays produced by hard primary rays are 

 very homogeneous and are absorbed according to an exponen- 

 tial law. Those produced by soft primary rays are not homo- 

 geneous, except for tin and silver, but consist of a large number 

 of corpuscles which are absorbed in the first '001 mm of alumin- 

 ium, and a smaller number which are not so easily, absorbed. 



5. In all the metals tested, with one exception, the ratio of 

 the number of corpuscles produced in the metal to the number 

 produced in lead for equal absorptions of the primary rays 

 was greater for metals of greater density. In silver, however, 

 the hard primary rays produced more corpuscles than in lead, 

 which has the greater density. 



6. The ratio JST/N/ depends partly, on the penetrating 

 power of the corpuscular rays and to a great extent on the 

 ratio of the absorption coefficients of the primary rays in lead 

 and the metal compared with it. Where the primary rays are 

 absorbed to a much greater extent in lead than in the other 

 metal, the corpuscles will be produced much nearer to the sur- 

 face in lead, and consequently more will escape from the lead, 

 if the corpuscles from the lead are not too much less penetra- 

 ting than those from the other metal. A good instance of 

 this is silver, where more corpuscles are produced than in lead 

 by the hard, primary rays, but yet more get out of the lead 

 than the silver. 



