McClkli.ano and Noi.an — The Elpciric Charlie on Rain. 87 



In the remainder of the paper we distinguish between three different 

 types of rain : — 



(a) Eain consisting of very small drops, as described above, and which 

 will be referred to as " fine " rain. 



{b) Eain consisting of relatively larger drops. This rain is generally 

 heavy ; but for our purpose, it is a question of the size of the drops, 

 and we have dealt with a rainfall as small as '0006 cm. per minute, 

 which clearly consisted of these larger drops. 



This type of rain will be referred to as " large " rain. 



(c) Eain consisting of a mixture of types (a) and (6). Eain frequently falls 

 which can be seen to consist of a mixture of large and very small 

 drops. This type we shall refer to as " mixed " rain. 



"Fine" Bain. 



As mentioned above, this type of rain consisting' of exceedingly small drops 

 was examined on fifteen separate occasions, aud found to be always negatiA-ely 

 charged. Although always negatively charged, the quantity of water falling 

 in this form and the negative electricity brought down by it is small, so that 

 its effect on the percentage of negative in the total charge brought down by 

 rain is not of much importance. In all we collected about 450 c.c. of rain of 

 this type. 



A feature of this type of rain is the relative constancy of the charge 

 per c.c. compared with the much greater variations of charge in the case of 

 larger positive drops. On many occasions this " fine " rain was heavy enough 

 to fill and tip the collecting-buckets ; and in such cases its charge per c.c. was 

 directly determined. On other occasions the rain was so slight that the 

 surface of the collecting-vessel was able to retain and evaporate all that fell 

 on it ; but the charge could easily be detected by the electrometer. On some 

 such occasions estimates of the charge per c.c. were made by exposing sheets of 

 blotting-paper of known surface area for short times and finding their increase 

 of weight. 



The maximum and minimum limits of the negative charge per c.c. 

 on " fine " rain were '24 electrostatic unit and "06 electrostatic unit ; and 

 tire mean value of all the determinations made was '12 electrostatic unit 

 per c.c. 



As we shall see later, the charge per c.c. on the larger drops varied between 

 much wider limits, and had a much greater mean value, 



