McClelland and Nolan — The Electric Charge on Rain. 89 



We noted on the occasions when very high charges per c.e. were present, 

 especially positive charges, that thunderstorm conditions appeared to prevail, 

 although no thunder was actually heard. 



"Mixed" Rain. 



With rain of this class there were cases as stated above when the electro- 

 meter deflections changed frequently from positive to negative, and many cases 

 when a charge always positive in sign, but small, was obtained. The follow- 

 ing Table (II) shows the percentages of the rain of this type having charges 

 between certain limits : — 





Table II. 







Charge per e.c. in Electrostatic 



Units. 



Pe 



rcentage 



L-1 





. 



17 



•1 - -5 







62 



•5-1 







17 



1-2 







4 



< 2 











Comparing this Table with Table I we see how much smaller the average 

 charge is in the case of the mixed rain. Quite possibly the very small drops 

 present in this mixed rain are always negatively charged even when the total 

 charge is positive; but as the negative charge per c.c. found on such small 

 drops when occurring alone is always so very small, we cannot directly 

 ascribe the relatively small positive charges we are now dealing with to the 

 fact that both positive and negative electricities are being collected. The 

 fact that the rain is of the mixed type points rather to the circumstances 

 attending its production being different from those in the case of the rain 

 consisting only of large drops. 



Potential Gradient Observations. 



It is well known that the normal positive potential gradient in fine 

 weather is greatly disturbed when rain is falling. This fact was fully 

 exemplified in our observations, the sign of the potential changing rapidly 

 and frequently. It is not correct to state, as is sometimes done, that during 

 rain the potential is negative. The noticeable feature is the frequent change 

 of sign that occurs. On the whole, we noted a negative potential more 

 frequently than a positive during rain. 



R.I. A. PKOC, VOL. XXIX., SECT. A. [12] 



