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LXIX. Notes on the Electrification of the Air near the Zambesi 

 Falls. By W. A. Douglas Rudge, M.A., Professor of 

 Physics, University College, Bloemfontein *. 



THE electrification of the atmosphere is always very 

 marked near a waterfall, and it seemed of sufficient 

 interest to take a series of observations in the neighbourhood 

 of what is probably the largest fall in the world. It is 

 hardly necessary to describe the structure of the fall, but it 

 may be noted that it possesses the peculiar feature of falling 

 over the side of the gorge rather than over one end. The 

 Zambesi just above the fall is nearly a mile and a half wide, 

 but at the fall it narrows to about 1900 yards. The width 

 of the chasm is about 350 ft., the depth 420 ft. The river 

 below the fall pursues a course at right angles to its original 

 direction, and a very energetic churning of the water ensues, 

 an enormous cloud of spray being formed, which may be 

 seen for many miles. The actual height of the cloud above 

 the gorge varies considerably, the maximum height noted by 

 the observer being about 600 ft. in the early morning, falling 

 to about one-third of this height at midday, increasing again 

 towards the evening. 



The instrument used in taking observations was an 

 electroscope of the Exner type attached to a telescopic 

 stand, so that its height above the ground could be varied, 

 a wire lipped with radium serving as the collector. Obser- 

 vations were taken at a fixed station and also at different 

 distances from the falls. 



Owing to the peculiar formation of the river-bed just 

 above the fall, it is possible to take observations at the 

 very edge of the fall itself, and also at various points in the 

 river above the fall, as well as from the side of the gorge 

 opposite ; but the results obtained in the immediate neigh- 

 bourhood are not of much value, as the charges obtained 

 were so great that the instrument used was incapable of 

 measuring them. A wire poorly insulated, and stretched 

 halfway across the gorge close to the bridge, about half-a- 

 mile from the fall, became so strongly charged that sparks 

 2 or 3 mm. in length were easily obtained from it. 



Observations at the Fixed Station. 



These consisted in taking the potential gradient at frequent 

 intervals. 



* Communicated by the Author. 



