30 Mr. J. Satterly on the Amount of Radium 



increase in the amount of radium emanation in the air, whilst 

 anticyclonic conditions, with dry or very cold weather, give 

 a decrease in the amount of the emanation in the air. This 

 he explains 



(1) by the spiral motions of cyclones and anticyclones, 



(2) by the suction action of changes of pressure on the 



emanation in the air lodged in the ground; 



(3) by the readier liberation of emanation from moist 



substances. 



My results are opposed to Eve's in this respect. I find 

 that cyclones accompanied by wet weather and strong winds 

 give a decrease in the amount of emanation, whilst anti- 

 cyclones accompanied by fine weather and light winds give 

 an increase in the amount. There are exceptions, but the 

 above is generally true, and the trajectories T have drawn 

 bear it out. 



Of course there is a great difference in the situations of 

 Montreal and Cambridge. The cyclones crossing England 

 come straight from the Atlantic, while those arriving at 

 Montreal have travelled over hundreds of miles of lund, and 

 this may explain the whole difference. If my experiments, 

 however, had each lasted 3 days, I should have found much 

 less difference between the maxima and minima values. 

 Ashman *, working at Chicago with the liquid air method, 

 made six measurements of the emanation content, and he 

 gets practically the same results as Eve. 



Most of the other workers in this subject have exposed 

 charged wires to the air, and measured the active deposits 

 obtained, the others have measured the atmospheric ioniza- 

 tion, &c. Dyke f, working at Cambridge for three weeks in 

 1906, drew a measured volume of air through a negatively 

 charged metal grid for an hour at a time, and found a 

 greater deposit on still bright days than on cloudy windy 

 days, and a small amount after rain. In California Harvey J 

 found the largest deposits occurred when a land wind blew 

 and the humidity was low, and the smallest deposits when 

 an ocean wind blew and the humidity was high. Work has 

 been done on the Continent of: Europe by Gockel§, Kohl- 

 rausch||, Sch\veidler% Amaduzzi**, Constanzoft* Simpson Jt, 



* Amer. Journ. Sci. Aug. 1908. 



t Terr. Mag-, and Atmos. Elec, Sept. 1906. 



X Le Radium, \\xx. 1909. 



§ Phys. ZeiUchr. May 1908. 



|| Akad. Wiss. Wien, Sitz.-Ber. Oct 1906. «j Ibid. 



** Accad. Lincei, Atti, Jan. 1909. 

 1 1- Phys. ZeiUchr. Mar. 1909. 

 X\ Phil. Trans. 1905. 



