t 148 ] 
changes; thus it is never at reft, but cOn- 
ftantly abting ; and by making a gentle 
impetus upon the conftituent parts of the 
machine, animates it, and fuftains it's 
life. 
The exiftence of the fluid I now fpeak 
of, is fupported by theory, and accords 
in the moft perfedt manner with the known 
laws of phyfics. I may go Hill farther, 
and give a demonftration of it, which 
carries along with it mathematical evi¬ 
dence. 
I deduce this demonftration from a dif- 
covery made fome years ago by Mr. 
Walfh on the gymnotus, and mentioned 
by M. Cavallo in his “ Complete Treatije of 
Eleffiricity but which neither he, nor 
any one elfe has, till now, been able to 
explain. This difcovery is, that the gym¬ 
notus is fenfible whether the fubftances 
brought near him arfe proper or not, for 
receiving the difcharge. 
The 
