26 o Dr. Wells's Observations on an Influence 
remark, that charcoal, though from its friability not very fit 
for the experiment, may yet be rendered capable by the same 
means of producing contractions, without the assistance of 
any of the metals. 
My next and last object is to inquire, whether the influence, 
which in all these experiments immediately excites the muscles 
to act, be electrical or not. 
The points of difference between any two species of natural 
bodies, even those which, from the similarity of some of their 
most obvious qualities, have once been thought the same, are 
found, upon accurate examination, greatly to exceed in num- 
ber those of their agreement. When, therefore, two sub- 
stances are known to have many properties in common, while 
their differences are few, and none of these absolutely contra- 
dict such a conclusion, we infer with considerable confidence, 
that they are the same, though we may not be immediately 
able to explain why their resemblance is not complete. After 
Mr. Walsh, for instance, had discovered, that the influence 
of the torpedo was transmitted by all the various bodies which 
are good conductors of the electric fluid, philosophers made 
little hesitation in admitting them to be one and the same sub- 
stance, though some of their apparent differences could not then 
be accounted for. In like manner, the inquirers into the na- 
ture of the influence, the effects of which are so evident in Mr. 
Galvani's experiments, have very generally, and in my opi- 
nion justly, allowed it to be electrical, on the ground that its 
conductors and those of electricity are altogether the same. To 
this, however, an objection has been made by Dr. Fowler, 
which, if well founded, would certainly prove them to be diffe- 
rent substances ; for he has asserted that charcoal, which is so 
