Dr. Eafon on the Afcent of Vapour. 401 
parched up with drought, and the roads covered 
wich duft.* 
It often happens, that one clap of thunder 
is not fufiicient to produce rain from a cloud, 
nor even a fecond : in lhort, the claps mud be 
repeated, till an equilibrium is restored, and 
then the rain mull, of confequcnce, fall. Some¬ 
times we may have violent thunder and light¬ 
ning without rain, and the black appearance of 
the heavens may be changed to a clear tranfparent 
fky, elpecially in warm weather. To account 
for this, it mull be remembered, as I lately 
faid, that one or more claps of thunder are not 
always fufhcient to produce rain from the clouds: 
fo, if an equilibrium be not reftored, little or 
no rain will fall, and in a lhort time, the elec¬ 
tric matter, palling from the earth to the clouds, 
or the fuperabundant quantity in the air, will 
electrify t'nofe black clouds, by which means the 
particles of vapour will be expanded, raifed 
higher, and the air become clear. Clouds 
may be melted away, even when we are look¬ 
ing at them, by another caufe, that is, by the 
* Saspe etiam immenfum coelo venit agmen aquarum. 
Et fcedam glomerant tempeftatem imbribus atris 
Collects ex alto nubes. 
Ipfe pater, media nitnbrorum in node, corufca 
Fulmina molitur dextra, quo maxima motu 
Terra tremit.. Virg. 
Vol. I. D d heat 
