[ 379 ] 
pierce, or only make impreffions upon it, in either 
cafe, they leave evident marks of motion from two 
different parts, and in two contrary directions. It is 
this deviation from a common courfe, and the fepa- 
ration of the lines of direction confequent upon it, 
that affords us the ftrongeft proof, of the exertion of 
two diftinCt and counteracting powers. 
3°. When two flips of tin-foil are put into the 
middle of the quire, including two or more leaves 
between them, if the eleCtricity be moderately ftrong, 
the counteracting powers only ftrike againft the flips, 
and leave their impreffions there. When it is ftronger, 
we generally find one of the flips pierced ; but fel- 
dom both : and from what I have obferved in fuch 
cafes, it would feem as if the power, which iflued 
from the outfide of the phial, aCts more ftrongly than 
that which proceeds from within ; for the lower flip 
is moft commonly pierced : But that may be owing 
to the greater fpace, the power from within has to 
move through, before it ftrikes the paper. 
I take the liberty to lay before the Society a paper- 
book, of the thicknefs of a quire, flruck three times in 
the manner above defcribed. The firfl flroke (A) is 
given, when there is nothing between the leaves of 
the book. The fecond (B) when a piece of paper, 
covered on one fide with what is commonly called 
Dutch gilding, is laid in the middle. The third 
(C), when two flips of tin-foil are put into the book, 
including the two middle leaves between them. 
The members, who are curious in thefe matters, 
may, at their leifure, examine the effects of the fun- 
dry ftrokes ; and if any gentlemen, in particular, de- 
fire the farther fatisfaCtion of feeing the flrokes given, 
C C C 2 I 
