[ 212 ] 
this property ; but this consideration had not been 
iufficiently attended to. 
* In the account of my former experiments on char- 
coal, I obferved, that there were very great differ- 
ences in the conducting power of charcoal, and 
particularly of wood charcoal, though I could not 
determine on what circumftances in the preparation, 
&c. thofe differences depended, I thererefore ex- 
preffed a with, that fome perfon, who had conveni- 
ences for making chemical experiments, would 
profecute the inquiry, as one that promifed, not only 
to afcertain the caufe of the conducting power of 
charcoal, but perhaps of conducting power univer- 
fally. Not hearing that any chemift or electrician, 
has attended to this bufinefs, I have, at length, re- 
fumed the fubjeft, though not with .every advantage 
that I could have wifhed. I have, in a great mea- 
fure, however, fucceeded in the principal object 
of my inquiry; and I fhall now lay before this 
Society, the refult of my experiments and ob- 
fervations. 
I fhall begin with correcting a miftake I lay under 
at the time that I made the former experiments. 
Having been informed by perfons, who attend the 
making of pit charcoal, that it was confiderably in- 
creafed in bulk after the procefs ; I imagined that all 
other fubftances received an increafe of bulk, when 
they were reduced to a coal ; but the firft experi- 
ments that I made, convinced me of my miftake. 
All vegetable fubftances are. confiderably contracted 
in all their dimenfions, by the procefs of coaling, 
and the more perfeCt this procefs is, that is, as will 
be explained hereafter, the greater heat is applied in 
