NATURAL HISTORY. 
of exciting the influence, which in 
those experiments occasions the 
miuscles to contract. But it ap- 
pears rather extraordinary, that 
none of those, who contend for the 
identity of this influence and the 
electric fluid, have ever suspected, 
that ‘the only very good dry con- 
ductor of the latter, which weknow, 
beside the metals, possesses like 
them the property of exciting the 
former. I confess, however, that it 
was not this consideration but acci- 
dent, which led me to discover that 
charcoal is endowed with this pro- 
perty, and in such a degree that, 
along with zinc, it excites at least as 
Strongly as gold with zinc, the most 
powerful combination, I believe, 
which can in this way be formed of 
the metals. - But, to prevent disap- 
pointments, I must mention, that 
_all charcoal is not equally fit for 
this purpose, and that long keeping 
_ Seems to diminish its power. 
It being shewn that charcoal is 
also to be ranked among the ex- 
citers of this influence, I shall now 
speak of the circumstances, in which 
both it and the metals must be 
placed, to fit them for the exercise 
of their power.- With respect to 
metals, Mr. Volta maintains, that, 
to this end, it is only necessary that 
two different ‘species be applied to 
any other body which is a good 
conductor of electricity, and that 
@ communication be established be-« 
tween the two metalic - coatings. 
But charcoal is a much better con- 
ductor of electricity than water, and 
~ yet metals in contact with it alone 
will not excite. Again, Mr. Volta 
says, that the simple application of 
_| two metals to two parts of an ani- 
.| mal, disturbs the equilibrium of the 
electric fluid, and disposes it to pass 
from one of the parts to the other, 
Vou, XXXVII. 
(*65 
which passage actually takes place, 
as soon as a conductor is applied 
between the metals. But what 
should prevent the passage of the 
fluid before the application of a new 
conductor, since the metals were 
already connected by means of the 
moisture of the animal? farther, 
a consequence of this opinion is, 
that, if the under surfaces of two 
different metals be placed in mois- 
ture, and their upper surfaces be 
afterwards connected by means of 
a nerve, still attached to its muscle, 
contractions ought then to be pros 
duced ; since the whole quantity of 
the electric fluid, necessary to re- 
store the equilibrium, which has 
been disturbed by the action of the 
metals, must pass through thenerve. 
This experiment I have made, and as 
I did not find the muscle to contract, 
I must hold Mr. Volta’s opinion, on 
this point, to be likewise ill-founded, 
The fact is, that as far as the con- 
traction of muscles is a test, whether 
the influence exists or not, and we 
have no other, it is never excited 
when two metals, or one metal and 
charcoal, are necessary for this pur= 
pose, unless these substances touch 
each other, and are also in contact 
with some of the fluids formerly 
mentioned. 
But there is still another requisite 
for the excitement of the influence, 
which is a communication by means 
of some good conductor of electrici+ 
ty, between the two quantities of 
fluid, to which the dry exciters are 
applied, beside that which takes 
place between the same quantities 
of fluid, when the dry exciters are 
brought ‘into contact with each 
other. As from this last circum- 
stance, a complete circle of con. 
nection is formed among the differ- 
ent substances employed, it has been 
[*E]} imagined 
