Greperal Reflections on Heai. 87 
n the present state of our kKnowledye, since we have dis- 
cdeéred 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. e shall find that they all agrec 
ina rapid’ combination of chemica! 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, itisa 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, 
see no objection: to our defining this precess, with Professor 
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 ledigth: 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 reflections on heat. Let. ci now pees 
this agent in its ecreesis 
Bo N ATURAL Sauuns 
‘We can nab find any thing in the Papier woeld. more 
evincive of design, or more indicative of the wisdom of the 
Creator, than the means used to keep up that uniform 
temperature, which, with some slight variations, is constantly 
maintained at the ‘surface of the earth. You are well ac- 
quainted with the power of heat to be yew meets by _ 
tural means far beyond what mortals could endure; and y 
are aware also of the fatalleffects which would pial rag se 
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 hatural ¢ course of things, 
without ever taking the trouble to inquire, whether any ma- 
