Excited in Air at the Foot of Waterfalls. 427 



a stream of air, when it was ionized by Rontgen rays and 

 directed against an insulated conductor, imparted to it a 

 negative charge owing to the greater velocity of diffusion of 

 the negative ions. These experiments, in which the gas was 

 in motion and the insulated conductor at rest, Schmauss con- 

 sidered the converse of his own. 



"Now, in the experiments we are considering, we have 

 water dropping through air which is known to be spontane- 

 ously ionized. From the results of Schmauss, we should 

 expect the spray to take up a negative charge from the air. 

 This, if sufficient to overcome the Lenard effect by which a 

 positive charge is developed through the impact of the spray 

 on the wire, should leave the wire negatively charged, and 

 this was the uniform result of the observations. 



4. — Radioactive Rain and Snow. 



In order to ascertain, if possible, the effects of variations 

 in the weather upon the radioactive state of the atmosphere, 

 the writer made a series of daily observations in the month 

 of November. During this period both rain and snow storms 

 occurred. The falling of rain was not found to produce any 

 marked change in the radioactive power of the atmosphere, 

 although, as already shown by 0. T. R. Wilson*, the rain 

 itself when tested was active. The falling of snow, however, 

 was accompanied by a very considerable drop in the value of 

 the excited radioactivity. For example, on Nov. 25th the 

 air was dry and cold, and the morning exposure gave a value of 

 0*92, that for the afternoon exposure being 66. The next 

 morning snow began to fall heavily, and an exposure was 

 made iu it for two hours. The resulting value for the excited 

 radioactivity was 0*3. The snow-fall continued throughout 

 the day, and the value for the afternoon exposure was again 

 0*3. This storm was general throughout Ontario, and the 

 snow, which fell to a depth of about three inches, remained 

 for some days on the ground and did not entirely disappear 

 until Nov. 30th. Tests made for radioactivity in the interval 

 showed values ranging from 02 to 0*4. On Dec. 1st an 

 exposure made about noon gave a value of 09. On this day 

 the weather was again mild and the snow had disappeared. 

 Exposures made in the mornings of Dec. 2nd, 3rd, 4th, and 5th 

 gave the values 0*8, 1*1, 0*9, 0*9 respectively. 



The weather continued mild until Dec. 5th, when the tem- 

 perature dropped below 0° 0. On Dec. 6th the cold weather 

 still prevailed and an exposure made from 1 to 3 o'clock in 

 the afternoon gave a value of 0*92,. Shortly after 3 o'clock 



* C. T. R, Wilson, Proc. Camb. Phil. Soc, vol. xi, Pt. 6, p. 428, 



