IB Proceedings of the Roijal Irish Academy. 



" fine " rain. This rain is made up of very small droplets, the volume of the 

 largest not being greater than 8 x 10"' c.c. It was found by them to be. 

 always negatively charged, and has been so in every instance in the present 

 investigation. It is generally very light, which makes the obtaining of 

 reliable observations on it rather difficult. Indeed a shower of it, lasting an 

 hour, oft«n failed to yield more than a few c.c. AVe were fortunate, how- 

 ever, in getting veiy heavy rain of this type in July and the early days of 

 August. Tliere was quite a downpour, lasting almost througliout the night 

 of July 21, the rate of rainfall being for a considerable time greater tlian 

 2"5 mm. per liour The chai-ge was negative throughout the night, and 

 varied from '001 to 04 E.S.U. per c.c. The abundance of this " fine " rain in 

 July accounts for the high percentage of negatively charged rain in that 

 montli, and also to some extent for the percentage of negative rain in the 

 period under observation. This is considerably higher than has been found 

 by any of tlie recent observers. Schindelhauer' found 92 per cent, of the 

 rain obser\ed by him positively charged ; Baldit,' 85 per cent. ; M'Clelland 

 and Nolan, 82*6 per cent. ; as has been stated above, the percentage of 

 positive rain in the present case is 73'5. If we neglect the July rain, the 

 percentage of positive rain is 86, which is nearer tliat found by other 

 obserA-ei-8. 



Most of the rain observed during the other months was of the " mi.xed " 

 type, i.e., it was a mi.\turc of drops of all sizes. It was generally positive; 

 but the charge sometimes became negative. Tliis change from positive to 

 negative seemed to occur irregularly at any period of the downpour or 

 sliower, though there was a tendency for the negatively charged rain to be 

 connected with a slower rate of rainfall, and perhaps with an increasing 

 number of smaller drops, tliough negative rain sometimes occurred with 

 quite large drops. The heaviest rain of this type was almost always posi- 

 tively charged. The transition from positive rain to negative was never 

 abrupt. The charge per c.c. always decreased before the change, and 

 often fluctuated from positive to negative for several minutes. During 

 these fluctuations the charge per c.c. was always small. Probably in such 

 cases some drops are positive and some negative. 



From the tables given above it will be seen that the positive charge is 

 generally much larger than the n^ative, on the average about double. The 

 months of April and June would appear to be exceptions, but in both these 

 months very few observations were got, and in each case all the negative 



' Schindelhauer, Veroffd. k. Preuss Met. Inst., No. 263. 1913. 

 » Baldit, Le Radium viii. April, 1911. ix. Slarch, 1912. 



