McClklland and Nolan — The Electric Charge on Rain. 65 



chargiiig is interrupted quite «uddenly, negative cliarges appear for a short 

 time, and then there is an abrupt return to the usual positive charges. The 

 occurrence of the negative charges appears to be associated more particularly 

 with the end of the shower, but this does not hold universally. Eain of this 

 "large" class is generally heavy, but the size of the drops is the chief 

 characteristic. It has seldom been observed during the mouths October to 

 February, _and appears to be generally accompanied by the conditions we 

 associate with thunderstorms. In the course of our experiments, however, 

 we have not had the opportunity of taking observations during a thunder- 

 storm. 



" Mixed, " Bain. 



In very decided contrast to the highly charged type cUscussed above is the 

 class of rain we previously distinguished as " mixed rain." Here the positive 

 predominates again. The values of the positive charge are, however, small, 

 the average being about "2 to 'S electrostatic unit per c.c. No liigh values 

 are found. The negative charge on this type of rain is even smaller, the values 

 obtained being usually less than '1 electrostatic unit per c.c, and most of them 

 being very much less. Jiothing, in fact, serves to separate out the two classes 

 of rain so clearly from one another as this disparity in the values of the 

 negative charges. As regards the size of the drops, this kind of raia would 

 well deserve the title of " mixed," but not as a mixture of two definite classes, 

 large and small ; but rather as a mixture of drops of all sizes varying from 

 the fairly large down to the very fine. The manner in which the negative 

 charges occur in this type of rain is, however, very suggestive of the idea of 

 a mixture of two types bearing opposite charges. In this case there is no 

 abrupt transition from large positive to large negative charges, but a gradual 

 shading from smaU positive into small negative values. There is much 

 lluctuation in the values of these small charges, and the changes of sign are 

 occasionally very frequent. It is often possible, as was pointed out in the 

 previous paper, to associate the appearance of negative charging with an 

 excess in the finer kind of rain. Again, rain of this sort often begins with 

 fine drops which are negatively charged ; but as it becomes hea^der, and the 

 drops increase in size, a positive charge is observed. It is not asserted that 

 this type of rain is always a mixture of two classes which are oppositely 

 charged, but rather that such a state of aiiaii's appears to exist frequently. 

 This particular type of rain occurs at all times of the year, but is especially 

 marked in the winter months, at which period the heavily charged type is 

 absent. It is frequently heavy, Imt has not the more violent characteristics 

 of the other type. It occurs often in a steady, continuous downpour, while 



