?>2 Mr. J. Satterly on the Amount of Radium 



Workers on the ionization in closed vessels include Campbell 

 and Wood* at Cambridge, Wulf t at Valkenberg in Holland, 

 Strong J at Baltimore, Pacini § at Sestola, Wright || and 

 Cline H at Toronto, and many others. Nearly all European 

 observers find a double daily variation in the ionization which 

 is closely parallel to the changes in the atmospheric potential 

 gradient. Wright (loc. cit.) and Cline, however, find no 

 evidence of a regular daily variation. Campbell and Wood, 

 Pacini and Cline agree in findino- that the ionization is 

 independent of the pressure, temperature, and humidity of 

 the air. When his vessel was not sealed Cline found that 

 the ionization was greatest when the atmospheric pressure 

 was lowest, and this he put down to the emanation sucked 

 out of the earth. 



The above results show that at present the subject is in a 

 confused state. It is desirable that instead of isolated 

 observers working on different points of the subject, well 

 equipped bands of observers at several laboratories should 

 thresh out the subject properly. Evidently much depends 

 on the locality at which the observations are made. Exposed 

 wires do not seem to lend themselves to great accuracy in 

 the measurement of atmospheric radioactivity, as there is 

 little knowledge of the actual volume of air which has con- 

 tributed to the deposit on the wire. Dyke's method seems 

 to be the best for measuring the active deposit, and the 

 charcoal absorption method for measuring the amount of 

 emanation in the air. 



Amount of Ionization of the Air due to the Radium 

 Emanation present. 



In my former paper I calculated that the radium emanation 

 in the air was, on the average, responsible for the formation 

 of 2*5 ions per c.c. per sec. Eve **, using later data for the 

 number of a particles shot out per sec. per gm. of radium 

 and its products, reduced this to 1*3 ions per c.c. per sec. 

 Recently Greiger ft nas determined afresh the average number 

 of ions produced by an a particle in its flight. He finds 

 that the average number of ions produced by an a particle 



* Phil. Mag. Feb. 1907. t Phys. Zefochr. Mar. 1909. 



t Phys. Review, Feb. & Julv 1908. § Accad. Lincei, AW, Feb. 1909. 

 || Phil. Mag. Feb. 1909. % Phys. Review, Jan. 1910. 



** Eve, ' Terrestrial Magnetism,' March 1909. 

 tt Geiger, Roy. Soc. Proc. vol. lxxxii., Julv 1909. 



