168 PHYSICS OF THE ELECTRON 



in consequence deduce that N =3.6 X 10 16 . Now ^ =2.0X 1(T 6 . Thus 

 <7 = 7.2X10 10 . Now the particles expelled from radium in a state 

 of radioactive equilibrium are about equally divided between four 

 substances, viz., the radium itself, the emanation, radium A and C. 

 We may thus conclude that the number of a particles expelled per 

 second from 1 gram of radium in radioactive equilibrium is 2.9X 10 11 . 

 The value deduced by this method is intermediate between the values 

 previously obtained (see previous table) on the assumption that the 

 heating effect is entirely due to the a particles. 



I think we may conclude from the agreement of these two methods 

 of calculation that the greater portion of the heating effect of radium 

 is a direct result of the bombardment of the expelled a particles, and 

 that, in all probability, about 5X 10 10 atoms of radium break up per 

 second. 



The energy carried off in the form of (3 and f rays is small compared 

 with that emitted in the form of a rays. By calculation it can be 

 shown that the average kinetic energy of the $ particle is small in com- 

 parison with that of the a particle. This result is confirmed by com- 

 parative measurements of the total ionization produced by the a and 

 /? rays, when the energy of the rays is all used up in ionizing the gas, 

 for the total ionization produced by the /? rays is small compared with 

 that due to the a rays. The total ionization produced by the f rays 

 is about the same as that produced by the /? rays, showing that, in 

 all probability, the energy emitted in the form of these two types of 

 radiation is about the same. From the point of view of the energy 

 radiated, and of the changes which occur in the radioactive bodies, 

 the a rays thus play a far more important role in radioactivity than 

 the /? or f rays. Most of the products which arise from radium and 

 thorium emit only a rays, while the /? and f rays appear only in the 

 last of the series of rapid changes which take place in these bodies. 



Since most of the heating effect of radium is due to the a rays, it 

 is to be expected that all radioactive substances, which emit a rays, 

 should also emit heat at a rate proportional to their a ray activity. 

 On this view, both uranium and thorium should emit heat at about 

 one millionth the rate of radium. It is of importance to determine 

 directly the heating effect for these substances, and also for actinium 

 radio-tellurium. 



According to the disintegration theory, the a particle is expelled 

 as a result of the disintegration of the atom of radioactive matter. 

 While it is to be expected that a greater portion of the energy emitted 

 should be carried off in the form of kinetic energy by the expelled 

 particles, it is also to be expected that some energy would be radiated 

 in consequence of the rearrangement of the components of the system 

 after the violent ejection of one of its parts. No direct measure- 

 ments have yet been made of the heating effect of the a particles, 



