268 



ATMOSPHERIC ELECTRICITY AT BLOEMFONTEIN. 



Date 



Max. 



Pot. 



Grad. 



Sept. 14 69 



„ 15 



lOI 



„ 16 48 



- 17 



„ 18 

 „ 19 



„ 20 

 „ 21 

 „ 22 



52 



52 

 180 



200 

 80 



152 



Time of 

 Max. 



8.20 la.m. 



7.30 a.m. 



7.30 a.m. 



7.50 a.m. 



7.50 a.m. 

 7.451a.m. 



8.15 a.m. 

 8.0 a.m. 

 8.25 a.m. 



Barometric Time of 

 Max. Max. 



Remarks. 



25.92 

 25.82 



25-75 



25.72 



2575 

 25.61 



25.6 



25-65 

 25.66 



10 



9 



ID 



10 



10 



10 



10 

 10 



No wind. 

 No wind ; mist 

 and cloud ; very- 

 variable. 

 II. 30 dust storm, 

 strong" negative; 

 11.40, zero ; 

 12.30, negative. 

 Dust most of the 

 day ; charge gen- 

 erally negative. 

 Dust most of the 

 day, as above. 

 Calm, thick mist, 

 variations, but 

 always -}-. 



The table shows the extraordinary daily variation in the 

 value of the potential gradient, and in particular the effect 

 of mist and dust must be noted. Presence of mist always raises 

 the potential and always shows that the charge in the air is 

 positive. Presence of dust at a distance lowers the positive 

 potential, and as the dust approaches gives rise to a negative 

 potential, and the magnitude of the negative potential is ihigher 

 than that ever reached by the positive potential.* A south or 

 south-etast wind is generally accompanied by a low potential 

 gradient. Only the morning maxima are given, and these gener- 

 ally occur ibetween 8 and 9 a.m., but many exceptions can be 

 noted, and the values given in the second colunm are the positive 

 ones ; if a negative charge occurred during the day it is noted in 

 the last column. On no day has the charge been entirely nega- 

 tive, at some time there has been a jjositive charge. The 

 'barometric variations are very normal, and there does not appear 

 to be any connection between the barometric pressure and the 

 \iariation of the potential gradient. The times of maxima show 

 no relation. 



* Save during thunderstorms. 



