phers sufficiently shew, that electricity is afforded 
by the simple contact of different bodies, by friction, 
and by other means, in which no chemical change 
takes place, and where, therefore, we have no evi- 
dence that any chemical action is exerted. But the 
excitation of electricity, by these mechanical means, 
does not disprove its development by chemical 
agency, any more than the extrication of caloric by 
friction or percussion disproves its liberation in the 
ordinary process of combustion* We therefore con- 
ceive, that the electric and calorific matter may be de^ 
veloped in bodies., both by chemical and by mechani- 
cal means ; and we consider this circumstance to 
yield no little support to that opinion of their simila* 
rity, which we have now been endeavouring to main* 
tain*. 
462. Thus, then, we see, from the foregoing state- 
ment and comparison of facts, that the calorific and 
chemical rays of solar light severally decompose and 
combine various bodies, precisely in the same manner, 
and with the same phenomena, as the different states 
or kinds of the electric fluid have been shewn to do ; 
* In the excitation of common electricity, indeed, both me- 
thods are usually called into action ; for the simple friction of the 
cylinder and rubber yields, in a mechanical manner, the elec:ririry 
that is supplied by the communication maintained with the earth ; 
while the amalgam furnishes, at the same time, a chemical source 
of electric matter, in consequence of the oxidation which it is 
made to undergo. And as, in combustion, the chemical combina- 
tion of oxygen is promoted by the communication of heat, so, in 
electrization, the oxidation of the amalgam must be facilitated by 
the electricity that is mechanically excited. 
