[ 3 6 ° ] 
By experience I found that the fame pair of dock- 
ings did not always do equally well, even indepen- 
dently of the weather j and that, by being too fre- 
quently electrified at a time, their virtue appeared to 
diminidi. I therefore judged it proper to be provided 
with changes of pairs ; and that there might be the 
greater conformity between the experiments, I chofe 
them as exactly as poffible of the fame fize and fub- 
ftance. The fort I fixed upon, is what is called half 
gauze; the weight of the white docking, at an ave- 
rage, 1 8 dwt. and io gr. but when died black, i oz. 
and i dwt. the weight being increafed, by the dying 
of that colour, above 5 dwt. in the pair. When the 
white and the black docking were warmed at the fire, 
fo as to be prepared for ele&ricity, they ufually lod 
about a twentieth part of their weight; fo that in the 
courfe of my experiments I rate the white at 17 
pwt. and I, and the black at 1 oz. The fcale, with 
the filk lines that belonged to it, and the hook, was 
adjuded precifely to the weight of 1 oz\ and as I 
commonly meafured the drength of cohefion by fix- 
ing the hook to the black docking, and taking hold 
of the white, I had but to make an allowance of 
2 oz. more than the weights put into the fcale, fo as 
to take the precife weight the dockings could raife 
by the power of cohefion. 
I meafured this power two different ways; the fiift 
whild the one docking was dill within the other; fc- 
condly, when feparated, and the one afterwards ap- 
plied externally to the other. In the fird of thefe 
cafes, it may be thought that an allowance diould be 
made for the friction in pulling the dockings afunder ; 
but that appeared to me to be very inconfiderable; for 
when 
