THUNDER STORMS. va 
natural quantities of it*, difcharge their furplufage to, or 
receive the neceflary fupplies from, either the earth or the 
neighbouring clouds, in fucceflive explofions, till an equi- 
librium is reftored between them. But I fhall endeavour 
in the following pages to prove, that thefe charges refide, 
not in the cloud or vapors of which it confifts, but in the - 
air which fuftains them; and that, previous to the for- 
mation of the cloud, or even the afcent of the vapors 
of which it is formed. But, in order to convey my ideas 
upon this fubject with perfpicuity, I find it neceflary to 
introduce them with a quotation from dotor Franklin’s 
letters on electricity, in which the doctor compares water, 
whether in its natural ftate, or rarefied into vapors, to a 
fponge; and the electric fluid, in comnetion with it, to 
water applied to the fponge. 
“© When a fponge (fays he) is fomewhat condenfed by 
being fqueezed between the fingers, it will not receive 
and retain fo much water as when it is in its more loofe 
and open ftate. If more fqueezed and condenfed, fome 
“ of the water will come out of its inner parts, and flow 
“ on the furface. If the preffure of the fingers be intire- 
ly removed, the fponge will not only refume what was 
lately forced out, but attra& an additional quantity. As 
the fponge in its rarer ftate will naturally attract and 
abforb more water ; and in its denfer ftate will naturally 
attract and abforb /e/s water ; we may call the quantity 
it abforbs in either ftate, its natural quantity, the flate 
being confidered.” 
The door then fuppofes, ‘ that what the fponge is to 
water, the fame is water to the electric fluid ;—that 
when a portion of water is in its common denfe ftate, 
it can hold no more electric fluid than it has; if any be 
added it fpreads upon the furface.” He adds, “ when 
the fame portion of water is rarefied into vapor and forms 
K 2 “a cloud, 
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* A body is faid to be ele&rically charged, whenever it has cither more or /-/ than its na- 
tural quantity of electric matter. 
