C *42 ] 
wider, and ftill wider when it diffolved into rain ; but 
their repelling power became greatefl in proportion as 
the drops increafed. 
The electrometer placed out from a garret window 
(p. 138.), has been frequently ufeful to me, in de- 
termining the nature of an approaching cloud, whofe 
electricity, although generally ftrong, was for the 
moft part uncertain, having been fometimes pcfitive , 
and at other times negative. But, as the wind or 
rain were frequent impediments to the accuracy of my 
experiments, the following methods of making obfer- 
vations, with fuccefs, under fhelter, occurred to me. 
I have fometimes ftood, in an upper room, on a 
cake of wax, holding in my right hand, out at the 
window, a long flender piece of wood, round which 
a wire projecting a few inches had been twifled, and 
in my left hand an electrometer: an affiflant had ex- 
cited glafs or wax in readinefs. 
At other times, I have made ufe of a tapering 
tube of tin, twenty feet long, ending in a point; the 
greatefl; part of it ftood out high in the air, and the 
thick end, from which an electrometer hung, was 
fupported infide the window, fometimes with filk 
cords, and at other times with flrong fticks of fealing- 
vvax, fuftained at either end by hooks of iron- wire. 
By either of thefe means I have often difcovered ? 
that what feemed to me a Angle cloud, produced, in 
its paffing over, leveral fucceliive changes, from pc- 
Jiiive to negative , and from negative to pcjitive elec- 
tricity, the balls coming together each time, and re- 
maining in contaCt a few feconds, before they re- 
pelled each other again. 
The 
