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obtained its charge part of it came down suddenly in the 
form of rain. As the rain came lower its electric tension 
would increase until it got near enough the ground to 
relieve itself with a flash of lightning, almost immediately 
after which the first rain would reach the ground. 
It has often been noticed that something like this often 
takes place; it often begins to pour immediately after a 
flash of lightning, so much so that it seems that the elec- 
tricity had been holding the rain up and it was only after 
the discharge that it could fall. This, however, cannot be 
the case, for the rain often follows so quickly after the flash 
that there would not have been time for it to fall from the 
cloud unless it had started before the discharge took place. 
If on the other hand C receded from E, it would again 
be in a position to accept more electricity, or would again 
become negative. In this way, a cloud in forming, or when 
first formed, would appear negatively charged ; soon after it 
would become neutral, and then if it moved to or from the 
earth it would appear positively or negatively charged. 
If the air was very dry, as it is in the summer, any 
exchange of electricity between the earth and the cloud 
would cause forked lightning, in the winter it would 
take place quietly, by the conduction of the moist atmo- 
sphere. 
In this way then there would sometimes be positive, 
sometimes negative lightning; sometimes the discharge 
would be a forked flash or spark, sometimes a brush or sheet 
lightning. And if clouds are formed in several layers, as 
would be represented by another conductor D outside C, 
then in addition to the phenomena already mentioned, 
similar phenomena would take place between C and D ; and 
if in addition to this we were to assume that there are 
