the weakeft Natural or Artificial Electricity. xxxiii 
nicated to other clouds, or vapours, or terreftrial prominencies. 
Thus a cloud may be electrified negatively, which cloud, after 
the fame manner, may occafion a pofitive eleCtricity in another 
cloud, &c. This explains not only the negative electricity, 
which is often obtained from the atmofphere in cloudy weather; 
and the frequent changes from pofitive to negative eleCtricity, 
and contrariwife in ftormy weather ; but alfo the waving mo- 
tion often obferved in the clouds, and the hanging down of 
them, fo as nearly to touch the earth. 
After the fore-mentioned difcoveries we need no longer won- 
der at the appearance of lightnings in the eruptions of volcanos, 
as was particularly obferved in the late dreadful eruption ol 
Mount Vefuvius. The few experiments I have made fihew, 
that the quantity of fmoke, but much more the rapidity with 
which it is produced, tends to increafe the eleCtricity which 
ariies from combuftion, &c How great mu ft then be the; 
quantity of electricity that is produced in fuch eruptions ? 
