386 DR. G. C. SIMPSON ON THE ELECTRICITY OF 



was falling in view of the routine work of the department. Nor do the coherer 

 records allow of such a division being made, for the coherer often recorded one or two 

 discharges on days when no thunder was heard and little rain fell. Thus the 

 difference between rain of this latter type which could not be called thunder rain and 

 that associated with much thunder and lightning was simply a matter of degree and 

 not of kind. For this reason the rainstorms have in the following analysis generally 

 been treated irrespectively of whether the rain was accompanied by electrical 

 discharges or not. 



Want of space makes it impossible to give here the detailed results of the 

 measurements. The figures are, however, to be published in extenso in part 8, 

 vol. 20, of the ' India Meteorological Memoirs.' 



Results. 



The aggregate amount of rain which fell during the periods of rainfall investigated 

 . was 76 '3 cm. 



The electrometer trace registered charged rain during 1926 two minutes' intervals, 

 during 13G2 of which the electrometer recorded positive electricity, and during 

 564 negative electricity. The total quantity of positive electricity which fell on each 

 square centimetre of surface was 22 '3 electrostatic units and of negative electricity 

 7 '6 units. 



From this it is seen that 2 - 9 times as much positive as negative electricity fell 

 during the rains and that the time during which positive rain fell was 2'4 times 

 longer than that during which negative electricity fell. This result is of great 

 importance in view of the generally accepted belief that much more negative than 

 positive electricity is brought down by the rain, a belief on which several theories of 

 atmospheric electricity have been based. 



When charged rain is falling the effect is equivalent to a vertical current of 

 electricity ; with positively charged rain the current may be considered to be flowing 

 from the atmosphere into the ground, and with negatively charged rain from the 

 ground into the atmosphere. The values of the currents attained in this way are of 

 considerable importance from the points of view of both atmospheric electricity and 

 of terrestrial magnetism. 



An analysis of the data for this purpose is given in Table I. 



In this table, column 2 contains the number of times positive currents (i.e. currents 

 caused by positively charged rain) were recorded with values between the limits 

 shown in the first column, and similar data for negative currents are given in 

 column 3. 



Neglecting for a short time currents greater than 300 X 10~ 15 ampere we see that 

 large currents are more seldom met with than smaller currents, this being true for 

 both positive and negative currents. The most important fact, however, is that as 

 the currents become larger the frequency with which positive currents occur tends 



