Excited in Air at the Foot of Waterfalls. 423 



The following numbers, which represent the observations 

 made upon one day, are typical and show this variation : — 



Exposure 9 a.m. — 11 a.m. 



Excited radioactivity *8 



„ 1 P.M. — 3 P.M. 



„ » '6 



„ 6 P.M. 8 P.M. 



i-o 



„ 9 P.M. — 11 P.M. 



I'l 



The observations were made in Toronto between Sept. 5th 

 and 12th, and between the 19th and 23rd, those made at 

 Niagara occupying the interval. The values in the two series 

 at Toronto exhibited similar variations and were confined in 

 both cases within the limits mentioned. The weather through- 

 out, except for a few showers, was uniformly fine. 



In conducting the experiments at Niagara Falls, the electro- 

 meter and its attachments were set up in the basement of the 

 landing-station at the foot of the inclined railway. It was a 

 large room having stone walls and a cement floor, and being 

 fairly dry, was well suited for making the tests. The elec- 

 trical machine which was intended for charging the wire w r as 

 also located in this room, and the wire to be exposed was led 

 from it out of a window and suspended in three stretches of 

 about 30 metres each, the insulation being secured as already 

 described. 



The situation was admirably adapted for making the ex- 

 posures, as the wire could be led within a metre or two of 

 the vast mass of falling water. The first length of wire was 

 generally enveloped in a very fine spray, that which surrounded 

 the second was heavier, while the downpour upon the third 

 resembled the heaviest rain. 



A point of peculiar interest in connexion with the first ex- 

 posure was that the wire, upon suspension in the spray, 

 immediately 'became negatively electrified to a potential of 

 about 7500 volts. This voltage was maintained with but 

 little variation both day and night during the period covered 

 by the experiments, and the sign of the electrification was 

 invariably negative. 



The results of a number of tests with the different sections 

 of the wire showed, that the removal of the third generally 

 caused a drop in the potential of the remaining sections from 

 7500 volts to about 5500 volts, while the first section, when 

 exposed alone, gave a potential varying from 3000 to 1000 

 volts. From this it was evident that the spray was the cause 

 of the electrification, and that the potential of the wire was 

 largely determined by its density. 



>n account of the permanency of this electrification of the 

 2 F 2 



