

Emanation given off by Radium. 361 
and that the number changing at any instant is proportional 
to the total number present. 
The ionizing power I may, from experiment (Rutherford, 
Phil. Mag. April 19038), be represented by 
i = I,K ae 
where A is a constant and ¢ the time measured from the 
instant when I = I). 
Since dl 
ee 
we see that X is the fraction of the total emanation that 
undergoes change or emits radiation in one second. And we 
know (Rutherford, Phil. Mag. April 1903) that I falls to half 
its value in about four days, so that \ is approximately equal to 
2 MOS 
If, therefore, we accept the theory that the emanation 
undergoes a further change and that each particle acts as a 
centre of radiation and ionization only when undergoing 
change,—and this is the only theory that seems to fit in with 
experiment,—vwe see that the number calculated above, giving 
the minimum ionization that must be produced by each 
emanation particle in one second, assuming it to be charged, 
would have to be multiplied by the factor 4. 10°. 
Multiplying 12000 by 3.10°, we get 6 x 10° as the 
minimum number of ions produced in one second by each 
emanation particle when its turn comes to disintegrate, 
assuming that it is charged. This number is not a possible 
one for several reasons. Rutherford (Phil. Mag. May 1908) 
gives 10° as the probable number of ions produced by each 
a ray before it is absorbed by the gas. The ionization is 
chiefly due to a rays, so that to produce the above ionization 
each emanation particle would require to emit 
9 
a : or 6 x 10* a rays. 
The mass of the e particle being of the same order as that 
of the hydrogen atom, and the emanation having been 
produced ‘by a disintegration of the radium atom, each 
emanation particle could not possibly emit more than about 
200 a rays. 
We can, therefore, finally conclude that the emanation 
not charged. 
This fact—that the emanation is uncharged—has an 
important bearing on our conception of the manner in which 
