Electric Deviation of Rays from Radium. 185 



The a rays from radium are thus very similar to the Canal 

 Strahlen observed by Goldstein, which have been shown bv 

 Wien to be positively charged bodies moving with a high 

 ve'ocity. The velocity of the a rays is, however, considerably 

 greater than that observed for the Canal Strahlen. 



General Considerations. 



The radiations from uranium, thorium, and radium, and 

 also the radiations from the emanations and excited bodies, all 

 include a large proportion of a. rays. These rays do not 

 differ much in penetrating power, and it is probable that in 

 all cases the « radiations from them are charged particles 

 projected with great velocities. 



In a previous paper* it has been shown that the total 

 energy radiated in the form of <x rays by the permanent 

 radioactive bodies is about 1000 times greater than the energy 

 radiated in the form of ft rays. This result was obtained on 

 the assumption that the total number of ions produced by 

 the two types of rays when completely absorbed in air, is a 

 measure of the energy radiated. The a rays are thus the 

 most important factor in the radiation of energy from active 

 bodies, and, in consequence, any estimate of the energy 

 radiated based on the ft rays alone leads to much too small 

 a value. 



Experiments are in progress to determine the charge 

 carried by the a. rays, and from these it is hoped to deduce 

 the rate of emission of energy in the form of a. rays from the 

 active substances. 



The projection character of the a rays very readily 

 explains some of their characteristic properties. On this 

 view the ionization of the gas by the a rays is due to 

 collisions of the projected masses with the gas molecules. 

 The variation of the rate of production of the ions with the 

 pressure of the gas and the variation of absorption of the 

 rays in solids and gases with the density at once follows. It 

 also offers a simple explanation of the remarkable fact that 

 the absorption of the x rays in a given thickness of matter. 

 when determined by the electrical method, increases with the 

 thickness of matter previously traversed. It is only necessary 

 to suppose that as the velocity of the projected particles 

 decreases in consequence of collision with the molecules of 

 the absorbing medium, the ionizing pov\er of the rays de- 

 creases rapidly. This is most probably the case, for there 

 seems to be no doubt that the positive carrier cannot ionize 



* Rutherford and .Grier, Phil. Mffg. Sept; 1902, 



