20 Dadourian — Radio-activity of Underground Air. 



ground air excited activity, the following experiments were 

 made : 



A piece of copper wire, J mm in diameter and 2 meters long, 

 was exposed to radium emanation in an apparatus shown in 

 figure 3. The apparatus consists of a glass bell- jar, A A, 22 cm 

 in diameter and 30 cm high. It is fitted with an insulating cap, 

 E, provided w T ith two binding-posts, F and G. The binding- 

 post F is in contact with a strip of tinfoil, DOB, and through 

 that with two other strips of tinfoil, CC and BB, all three 

 being pasted inside the bell-jar. J is a flask containing a solu- 

 tion of radium bromide of 1000 activity, prepared by De Haan. 

 A glass tube, I, provided with a glass stopcock, is connected by 

 a piece of rubber tubing to another tube, H, which passes 

 through the insulating cap, E, into the bell-jar and puts the 

 latter in communication with the flask which contains the 

 radium solution. Another flask, M, is connected with the flask 

 J through two glass tubes, K and L, joined by a piece of rub- 

 ber tubing carrying a screw pinchcock. Another piece of rub- 

 ber tubing carrying a screw pinchcock connects a funnel, O, 

 to the flask M. 



The wire to be exposed to radium emanation was loosely 

 coiled and was hung from a hook soldered to the lower end of 

 the binding-post G. The latter was connected to the negative 

 electrode of a storage battery of 100 volts, while the binding-post 

 F was connected to the positive electrode of the battery. Thus 

 an electric field was set up within the bell-jar. Then some 

 water was poured into the funnel and the pinchcock, P, was 

 regulated such that the water dropped into the flask M, drop 

 by drop. Each drop displaces an equal volume of air, which 

 bubbles out through the radium solution. This bubble in its 

 turn forces part of the mixture of air and radium emanation 

 in the flask J to go into the bell-jar. Thus the bell -jar is sup- 

 plied uniformly with radium emanation. This rather elaborate 

 method of exposing the wire to radium emanation was used to 

 guard against particles of radium which might otherwise come 

 into contact with the wire or the bell-jar. After the wire was 

 charged for exactly three hours it was taken out of the bell-jar, 

 was introduced into the testing cylinder and observations of 

 the ionization currents were taken as described above. The 

 results of the experiment are shown by curve III, figure 2. 



The rate of decay of thorium excited activity also was taken 

 by exposing a piece of copper wire, of the same dimensions as 

 the one used for radium excited activity, to thorium emana- 

 tion. The source of the emanation was about 10 grams of 

 powdered thorium oxide, which was spread uniformly over a 

 watch-glass and placed under the bell-jar. The wire was 



