
362 RADIO-ACTIVITY OF THE ATMOSPHERE [CH. 
the emanations obtained from the water and soil was carefully 
measured, and within the limit of experimental error agreed with 
the decay of activity observed with the radium emanation. The 
identity of the emanations from the water and soil with the 
radium emanation was still further established by experiments 
on the rate of diffusion of the emanation through a porous plate. 
By comparative tests it was found that the coefficient of diffusion 
of the emanations from the water and soil was the same as for 
the radium emanation. In addition, by comparison of the rate of 
diffusion of carbonic acid, it was found that the density of the 
emanation was about four times that of carbonic acid, a result in 
good accord with that found for the radium emanation (section 
153). 
213. Radio-activity of constituents of the earth. Elster 
and Geitel’ observed that, although in many cases the conductivity 
of the air was abnormally high in underground enclosures, the 
conductivity varied greatly for different places. In the Baumann 
Cave, for example, the conductivity of the air was nine times the 
normal, but in the Iberg Cave only three times the normal. In a 
cellar at Clausthal the conductivity was only slightly greater than 
the normal, but the excited radio-activity obtained on a negatively 
charged wire exposed in it was only 1/11 of the excited radio- 
activity obtaimed when the wire was exposed in the free air. It 
was concluded from these experiments that the amount of radio- 
activity in the different places probably varied with the nature. 
of the soil. Observations were then made on the conductivity of 
the air sucked up from the earth at different parts of the country. 
The clayey and limestone soils at Wolfenbiittel were found to be 
strongly active, the conductivity varying from four to sixteen times 
the norma] amount. A sample of air from the shell limestone of 
Wiirzburg and from the basalt of Wilhelmshdhe showed very little 
activity. 
Experiments were made to see if any radio-active substance 
could be detected in the soil itself. For this purpose some earth 
was placed on a dish and introduced under a bell-jar, similar to that 
shown in Fig. 59. The conductivity of the air in the bell-jar 
1 Phys. Zeit. 4, p. 522, 1903. 

