36 General Reflections on Heat. 
them on the retina of the eye. But the knowledge of this 
fact has enabled him, with the telescope, to carry the range 
of his dim eye beyond the stars; or, with his microscope, to 
read, with no less astonishment. the wondrous volume of ier- 
restrial nature. Who does not know that heat will convert 
water into steam? Yet it was the philosopher oily who, by 
studying all the circumstauces or laws of this change, taught 
how, with this substance, to bear the loftiest ship through 
the waves, and to disembowel the earth itself. 
‘<' But Lavoisier, ambitious to account for every thing. and 
A not, like Newton, being ready to rest satisfied with the dis- 
Tae covery of causes ee without attempting to explain their 
Oa connexion with the effects wh:ch they produced, proceeded 
to attempt an explanation of the reason why the combination 
of oxygen with a combustible base should produce light and 
heat. This he did, by referring it to the condensation which 
the gas was supposed to undergo, its base only entering into 
combination, while the light and heat that were before 
united with it, were set at tiberty. Condensation, however, 
is by no means an invariable antecedent to the production of 
light and heat in combustion. In the course of our experi- 
ments, gentlemen, you have witnessed a number of examples 
of this process where the evolution of light and heat was at- 
tended with a great rarefaction of the ingredients. I need 
only refer you to the inflammation of gunpowder, to the ex- 
plosion of the julminating powders, to the action of nitric 
acid on spirits of turpentine, and of the solid nitrates on the 
metals, as that of nitrate of copper oa tin foil, or of nitrate of 
potash on melted tin. But even if it could have been shown, 
that condensation is always an antecedent of light and heat 
in combustion, it would only be ascertaining a general fact 
exactly analogous to this, that oxygen is an invariable antece- 
dent io the same process. We can no more assign a reason 
why condensation should produce light and heat, than why 
the combination of oxygen with a combustible base should 
do it. The idea that the heat is mechanically forced out by 
compression, like water from a sponge, is ‘a crude idea,” 
wholly incompatible with the known subtilty of that agent ; 
and. moreover, that there is no necessary connexion between 
condensation and the production of light and heat, is manifest 
. from the fact, that light and heat sometimes, as in several 
cases cited above, accompany rarefaction. 
