which incites the Muscles of Animals to contract. 257 
opinion, is another fact I discovered in pursuing this subject; 
which is, that an exciting power may be given to a metal 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, doubt- 
less, 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 substances, upon which the fric- 
tion was made, were either electrics, or imperfect conductors 
of electricity ; I once thought it possible, that the metal sub- 
jected to the friction had acquired by means of it an electrical 
charge, which, though very slight, was still sufficient to act as 
a stimulus upon the nerves to which it was communicated. 
But that this was not the case was afterwards made evident,, 
by the following experiments and considerations. 
1. A metal, rendered capable by friction of exciting con- 
tractions, produced no change upon Mr. Bennet's gold-leaf 
electrometer. 
2. The interposition of moisture does not, in any instarice I 
know of, increase the effect of friction in exciting the electric 
fluid. In some instances it certainly lessens this effect. But 
moistened substances, when rubbed by a metal, communicate 
to it the capacity of producing contractions, much more readily 
than the same substances do when dry. 
3. If my hand, from being an imperfect conductor, had oc- 
casioned an accumulation of electricity in the metal which 
vvas rubbed, a greater effect of the same kind ought certainly 
