﻿in the Earth and the Atmosphere. 7 193 



between * 1 4 and *5 gram. This quantity, which may be denoted 

 by R, has been determined by a method which is quite 

 independent of any theory of the radioactivity of the 

 atmosphere. It was found by measuring the radiation from 

 the active deposit on a negatively charged wire placed in a 

 large vessel. The lower value, '14, was that obtained by 

 observations in the open air, and is probably the more correct. 

 But since it is desired at the present moment to find a higher 

 limit, let the larger value of R, namely *5 gram, be taken. 

 Then from the result (4) it is easy to calculate the total 

 number of ions produced per second in a cubic kilometre of 

 the atmosphere due to the 7 rays from the active matter in 

 it. The calculation will be made on the supposition that an 

 infinite volume of air contains emanation, to the amount per 

 c. k. above stated, uniformly distributed throughout it. A 

 little consideration will show that a volume distribution gives 

 results identical with distribution at points. 



The number of ions produced per c. k. per second is 



•5 x 8"9 X 10 14 



or '44 ions per c.c. per second. 



It is clear that at the earth's surface, which is a boundary 

 of the atmosphere, one-half of the above value should be 

 taken, or '22 ions per c.c. per second. 



A more probable value is 14/50 of this, or '06 ions per 

 c.c. per second. In any case we must conclude that the 

 ionization due to the 7 rays of the active matter in the atmo- 

 sphere is almost a negligible quantity and quite inadequate 

 to account for the relatively large effects due to penetrating 

 radiation observed by Cooke. Campbell, and others. For 

 example, in a well-cleaned brass vessel, H. L. Cooke found 

 q = 13*6 *, and by a screen of about 5 cms. of lead he was able 

 to reduce this value to 9*1. No further reduction could be 

 effected by thicker screens, so that about 4*5 ions per c.c. are 

 produced in a brass vessel every second by the penetrating- 

 radiation near the surface of the earth. Campbell appears to 

 find even larger results from this cause. Since it has been 

 shown that the 7 rays from the active matter in the atmosphere 

 are quite insufficient to account for such large effects, let us 

 consider the penetrating rays due to the active matter in the 

 crust of the earth. If, for instance, radium is mixed with 

 solid matter such as sand, or found in an ore, the penetrating 

 radiation from the radium in the body would be larger than 



* The amount originally stated was 7*5, but on the assumption that 

 the ionic charge was 6-8 X 10- 10 . 



Phil. Mag. S. 6. Vol. 12. No. 69. Sept. 1906. 



