Gsenerai Reflections on Heni. od 
In the present state of our knowledge, since we have dis- 
covered that oxygen is not the only supporter of combustion, 
we are prepared for a new classification of these phenomena, 
and must search out some circumstance in which all the 
cases of combustion agree. We shall find that they all agree 
in a rapid combination of chemical elements. In some cases, 
as in the fulminating powders, considerable masses enter into 
new combinations instantaneously ; in all other cases of ac- 
tual combustion, the union of the elements is more or less 
rapid; and finally, it is a general law, that the union of the 
same elements, as oxygen and iron for instance, will take 
place, when slow, without, and when rapid, with combustion. 
In order therefore to express the only invariable antecedent, 
with which we are acquainted, to all cases of combustion, I 
see no objection to our defining this process, with Professor 
Brande, thus: COMBUSTION IS THE RESULT OF INTENSE 
CHEMICAL acTION. It has been objected to this definition, 
‘that it explains nothing ;’ and that is true; it does not ex- 
plain, or attempt to explain, why combustion should result 
from intense chemical action; it merely states the fact, that 
this is, so far as we can see. the invariable antecedent under 
which the several species of combustion may be united ina 
class. 
The lepgth into which we have been drawn in reviewing 
the important subject of combustion, has made us almost lose 
sight of the other topics which we proposed to consider, in 
our general reffections on heat. Let us now contemplate 
this agent in its relation, 
n To Naturat TEMPERATURE. 
We can hardly find any thing in the natural world more 
evincive of design, or more indicative of the wisdom of the 
Creator, than the means used to keep up that uniform 
iemperature, which, with some slight variations, is constantly 
maintained at the surface of the earth. You are weli ac- 
quainted with the power of heat to be accumulated by na- 
tural means far beyond what mortals could endure; and you 
are aware also of the fatal effects which would result from the 
reduction of temperature below its ordinary limits. But, ac- 
customed to see the variations of temperature on the surface 
of the earth limited to so small a scale, you might content your- 
selves with thinking that this was the natural course of things, 
without ever taking the trouble to inquire, whether any ma~ 
Pas 
