372 Taylor — Retardation of Alpha Rays by Metals. 



2. The air-equivalents of hydrogen cells or sheets increase 

 as the speed of the entering particle decreases, while the air- 

 equivalents of sheets of paper and celloidin remains constant. 



3. The hydrogen-equivalents of sheets of paper, films of 

 celloidin, and air do not remain constant but decrease as the 

 speed of the alpha particle decreases. The rate at which the 

 hydrogen-equivalent of a celloidin film decreases with the 

 speed of the entering a-particle is numerically equal to the 

 rate at which the air-equivalent of a hydrogen sheet of corre- 

 sponding thickness increases. 



4. The result obtained by Bragg, that the total ionization 

 produced by the alpha particle in air is the same as that in 

 hydrogen, is confirmed by a more direct method. 



5. It is very probable that for the high ranges the a-particle 

 loses its energy, in passing through substances, more/rapidly 

 the higher the atomic weight of the substance ; but that this 

 difference decreases slowly until in the low ranges the loss of 

 energy is the more rapid the lower the atomic weight of the 

 substance. 



6. A comparison of the Bragg carves for air and hydrogen 

 indicates that the large ionization at low ranges (knee of the 

 curve) is due at least in part to the fact that the particle loses 

 its energy more rapidly in this part of the range; and not 

 wholly to the higher ionizing efficiency of particles of low 

 speed. 





