Electrification of the Air near the Zambesi Falls. 613 

 Table I. 

 Potential Gradient at Fixed Station. 



Time. 



Height of 

 Electroscope 

 above ground. 



Charge. 



Potential 

 difference 

 in volts. 



P.D. 



per metre. 



6.38 a.m 



7.0 



160 cms. 



>> 

 >> 



>> 

 )> 



>» 



4- 



4 

 4- 

 4- 

 4- 

 4- 

 4- 

 4- 

 4- 

 4- 

 4- 

 4- 

 4- 

 4- 



+ 



75 



75 

 175 

 200 

 250 

 375 

 500 

 250 

 510 

 525 

 275 

 175 

 



25 



25 



25 



40 



50 



50 

 100 

 120 



0? 

 150 

 150 

 125 

 140 

 100 

 100 



47 

 47 

 110 

 125 

 156 

 237 

 314 

 156 

 317 

 330 

 171 

 110 

 



16 

 16 

 16 

 25 

 31 

 31 

 62-5 

 75 

 

 93 

 93 

 78 

 88 

 625 

 625 



7.17 



7.20 



7.23 



7.25 



7.27 



7.30 (1) 



7.50 



8.0 



8.30 



9.00 



10.30 



1 



2.0 r.M 



230 



2.45 



3.30 



4.0 



4.30 



5.00 



60 



6.30 (2) 



6.35 



6.45(3) 



7.00 



8.40 



9.50 



10.30 





Between 10.30 and 2 the charge was very small. 



of the river. At the end nearer to the falls, the electroscope 

 was at once charged to the maximum, while at the further 

 end it had a value of only 600 to 800 volts per metr?. 



A set of observations was next taken at different distances 

 from the falls, starting from the fixed station at a time when 

 the electrification at that place was at a minimum. Distances 

 were measured by pacing, and detours had to be made in 

 order to obtain spaces free from trees ; therefore the results 

 are only approximate. The total distance between the fixed 

 point and the falls was about 2,500 paces, and observations 

 were made at intervals of J 00 paces, with the result shown 

 in the table. After 1000 paces had been made, the charge 

 was too great to be measured directly by the instrument, so 



