612 Prof. W. A. Douglas Rudge on the 



The potential varied enormously but to some extent uni- 

 formly with the time, and changed sign during the morning. 

 Observations were begun before sunrise 6.30 to 7, and were 

 continued at intervals up to 10 p.m. The position chosen was 

 such that the cloud from the falls intervened between the 

 observer and the rising sun. In the early morning at a 

 distance of about one mile from the fall the charge was 

 negative. The amount of electrification depended upon the 

 joint effect of the sun and the cloud, a large increase being- 

 seen when the rays of the sun were able to break through 

 the cloud. The maximum was reached when the position of 

 the sun allowed it to shine above the cloud. During the 

 whole period of observations, the sky was quite free from 

 ordinary clouds. The maximum electrification occurred at 

 about 8 a.m., though no quite precise time can be stated, for, 

 as might be expected, the wind had a very appreciable 

 influence. From 8 o'clock the potential fell and reached a 

 minimum value about 10.30 at the station where the obser- 

 vations were made, but when the electroscope was carried 

 nearer to the falls, the potential rose to a negative value ; 

 and on taking the instrument some distance further from 

 the falls, a slight positive electrification was obtained. From 

 this period on to 2 P M. the electrification was nearly always 

 zero, but afterwards a positive value was developed. 



As the country round the falls is thickly wooded, obser- 

 vations could only be taken satisfactorily where free from 

 trees. The fixed station was at a height of about 100 ft. 

 above the falls, and no high trees intervened, or, rather, the 

 line drawn from the station to the falls' cloud passed well 

 over the intervening trees. At 6 P.M. the positive electri- 

 fication was well-marked, and it increased in value up to 

 7 o'clock, after which it fluctuated, falling once or twice to 

 zero and changing sign. At 9.50 it was positive. 



In the evening when the charge was positive at the fixed 

 station, it was still as strongly negative near the falls ; the 

 sign changed at about 2000 paces from the falls. 



Observations were taken in a canoe at points on the river 

 above the falls. At a distance of a mile above, the value 

 had fallen to zero, at which it remained for a considerable 

 distance. At 7i miles above, a landing was made upon a 

 rock in the rapids, and here the electrification was decidedly 

 positive but comparatively small in amount — 100 volts per 

 metre. The potential falls very rapidly above the falls. 

 Livingstone Island is perched at the very edge of the fall, 

 and is about 200 yards in length measured in the direction 



