General Reflections ow Heat. 81 
Combustion, more intelligible, it will be necessary to insti- 
tute the inquiry, When ts a phystcal fact or phenomenon ad- 
equately accounted for? tis accounted for when it is shown 
io be similar to a number of other phenomena, which are ai- 
ready arranged under a general fact, with which they are 
known to be invariably connected, and which is therefore 
considered as their cause. Thus we account for the sound 
of a violin by classing it among those phenomena which are 
known to be invariably connected with vibrations of the air: 
and since this circumstance—namely, vibrations of the air— 
has been found to be connected with all those cases of sound 
which have been investigated, we are led to believe that it is 
2noariably connected with it, and therefore denominate it, 
universally, the cause of sound. It Is evident that we account 
for the sound of the violin, merely by classing it among 
phenomena that are known to be connected with vi- 
brations of the air; for in this individual instance, we do net 
examine to see whether the air undergoes vibrations or not. 
If we proceed one step further and inquire why vibrations 
of air upon the organs of hearing should produce the sensa- 
tion of sound, we are utterly unable to assign tbe reason: 
this inquiry leads us to ultimate causes, which are known to 
exist by their effects, but their existence is all that we can 
learn respecting them. In most cases before we reach the 
ultimate cause, we pass through a series of causes and effects, 
or antecedents and consequents, and deem each effect in 
order adequately accounted for, when we show its invariable 
connexion with its immediate antecedent. Thus we account 
for the movement of a steam-boat by the turning of the 
wheels in the water ; for the motion of the wheels, by the 
ascent and descent of the piston; forthe ascent and descent 
of the piston, by the elastic force of steam, and its power of 
forming a vacuum by condensation ; and, finally, for the elas- 
ticity of steam, by the agency of heat. This brings us to 
one of those general forces in nature, whose existence is 
known from their effects, but to which we can assign no an- 
tecedent. Here then our series of antecedents and conse- 
qe n ts, or causesand effects, terminates ; and we in vain look 
for a reason why heat should impart elasticity to steam. The 
principal difference between philosophers before and since 
the time of Lord Bacon, consists in the different order they 
would pursue in investigating phenomena like the foregoing: 
The ancient chemists would have begun at heat, and would 
Vou. X.—No. 1. i! 
