NATURAL HISTORY. 
@ portion of the nerve without en- 
tering the muscles. Having finished 
this experiment, I immediately af- 
ter applied the same probe between 
the silver coating of the nerve and 
the naked muscles, and was sur- 
prised to see these contract. A se- 
cond and third application were 
followed by the same effects, but 
farther applications were of noavail. 
It then occurred to me that motions 
might re-appear, if I again touched 
the two coatings with the probe, 
and the event proved the conjecture 
to have been fortunate; for, after 
every application of the probe to 
the two coatings, contractions were 
several times excited by it. The 
fact being thus established, that, un- 
der certain circumstances, contrac- 
tions could be produced by silver 
alone, it next became a subject of 
inquiry, whether this was owing to 
any disposition of the muscles and 
nerve, which had been induced 
upon them by Mr. Volta’s experi- 
ment, or whether, the condition of 
the muscles and nerve being unal- 
tered by that experiment, the silver 
had gained some new property by 
coming into contact with the tin-foil, 
The point in doubt was soon deter- 
mined, by applying the probe to a 
piece of tin-foil, which had no con- 
nection with any part of the animal; 
for, when this was done, it was 
again enabled to produce contrac- 
tions. As these experiments, how- 
ever, frequently did not succeed 
when made upon other frogs, I af- 
terwards varied the metals, and 
found in consequence, that zinc, 
particularly if moistened, communi- 
cated an exciting power pretty 
constantly to silver, gold, and iron. 
If any of these metals were slightly 
rubbed on the zinc, they almost 
always acquired such a power. 
[67 
It will, perhaps, be thought, from 
the last-mentioned circumstance, 
that, in every instance of motion 
being in this way produced, it was 
in truth owing to some part of one 
of the metals having been abraded 
by the other; so that, under the ap- 
pearance of one metal, two were in 
reality applied. But it can scarcely 
be supposed, that, from touching the 
polished surface of tin-foil in the 
gentlest manner with the smooth 
round end of a silver probe, any part 
of the former metal was carried 
away by the latter; and even when 
friction was used, as the zinc was 
much harder than the gold and 
silyer, it is not probable that it was 
in the least abraded by them. Be- 
sides, moisture, as I have already 
said, increases this effect of friction, 
though it lessens friction itself. 
The most powerful argument, 
however, in favour of my opinion, is 
another fact I discovered in pursuing 
this subject ; which is, that an ex- 
citing power may be given to a me- 
tal by rubbing it on many substances 
beside another metal, such as silk, 
woollen, leather, fish-skin, the palm 
of the human hand, sealing-wax, 
marble, and wood. Other substances 
will, doubtless, be hereafter added 
to this list. 
As the metals while they were 
rubbed were held in my hand, which, 
from the dryness of its scarf-skin, 
might have afforded some resistance 
to the passage of small quantities of 
the electric fluid ; and as the sub. 
stances, upon which the friction was 
made, were either electrics, or im- 
perfect conductors of electricity ; I 
once thought it possible, that the 
metal subjected to the friction had 
acquired,by means of it,an electrical 
charge, which, though very slight, 
was sul sufficicut to act as a stimu. 
f*E2 ) lus 
