a“ General Reficctions ov Heat. 
have endeavoured to deduce all the phenomena from reasou~ 
ing on the nalure of that agent; the modern chemists, pursu- 
ing the reverse order, end at beat, satisfied that they have ac- 
counted for each effect, when they have ascertained its inva- 
riable antecedent. 
e may assert in general, then, that a fact in chemistry i is 
adequately accounted for, when we have ascertained its in~ 
variable antecedent; but since the process. would be tedious 
to do this for every chemical change, by an analytical exam- 
ination of the result, we refer .each pease, change to a 
class of phenomena which it resembles, of w ee rn 
number have been examined, to show their saenarable con- 
nexion with their antecedent. Thus, when we hold melted 
lead over the fire ina ladle, we account for the dross that 
forms on its surface, by saying that the lead has combined 
with oxygen; not because we have, in this instance, ascer- 
tained the fact, but because its external appearance is suc 
as to justify usin classing it among similar phenomena, where 
the fact has been ascertained by actual experiment., This is 
another fact to’ show, that our explenations of phenomena are 
little else than mere classifications. ‘The same remark hold 
true in.every department of physics : we account for a phy- 
sical fact by assigning its ew cause or antecedent ; but 
we ascertain this, not sofrequently by actual experiment, as 
by reducing the fact in question to a class of phenomena, 
whose cause has been ascertained by actual experiment. . 
With these principles in view, let us now proceed to in- 
quire how far Lavoisier accounted for the phenomena of 
-[tappears to me, that Lavoisier must have been 
considered as ade equately accounting for combustion, pro- 
vided that the combination of oxygen with a base had always 
_ proved to be, as it appeared to him, an invariable antecedent 
to that process. In the progress of our, science, however, 
a number of examples of cpaladees have been discovered, 
in which no oxygen is present. Thus certain substances 
burn in an atmosphere of eulpbueatiog hydrogen, or chlorine, 
or iodine ; and even certain solids into which no oxygen 
seer as sulphur and -iron filings, or sulphur and copper 
filings, exhibit similar phenomena in their action on each 
other. Oxygen therefore has now lost its character of inva- 
riable autecedent, and its combination with inflammable 
bodies san pe longer be pronounced the cagse of combustiea. 
at . 
Ce a a SE RE Oe a Siete imac ee 
