[ 35 ® ] 
To give a didindt account of the eledlricity of Hack 
and white filk, I (hall trace it through its whole pro- 
cefs, beginning before the (lockings of the different 
colours are put together. 
After being a little air’d at the fire, when the black 
filk is drawn fingle upon the hand, a crackling noife 
is heard]; and in the dark, fparks of fire may be per- 
ceived as palling between the hand and the (locking : 
while it is drawn backwards and forwards the crack- 
ling continues, and is moll confiderable upon the fe- 
paration of the (locking from the hand. Thus it ap- 
pears, that black filk is highly fufceptible of ele&rici- 
ty ; that it is produced almod inflantaneoufly, or at 
lead with very little fridlion; that mod of it efcapes, 
while the docking is yet upon the hand ; and that, 
upon the total feparation, very little remains. This is 
fimilar to what happens with the giafs tube, when the 
hand, after pading along it in one direction, repafies 
it in the other. But dill the eledlricity that the dock- 
ing retains, after it is feparated from the hand, is con- 
fiderable enough to attract or repel little light bodies 
at the didance of one or two feet; fome degree of 
inflation in the docking is likewife perceiveable ; and 
when a non-eledlric is brought near it, a crackling is 
heard, and in the dark fparks may be feen. If two 
black dockings be drawn upon the hand at a time, 
the appearances are much the fame as before ; only 
that the dockings, when taken off and feparated, give 
fmaller proofs of eledlricity, than if each of them had 
been fingle upon the hand. 
Having found it neceffary, as I proceeded in my 
courfe of experiments, to fix upon fome method of 
afeertaining the principal appearances of ele&ricity, 
and 
