LATENT HEAT IN STEAM. 365 
orates naturally or artificially, it must appropriate to itself, 
in order to be transformed, and it does attract from the 
surrounding bodies, 535° of heat. And these degrees, it 
cannot be too often repeated, are integrally restored by 
steam on whatever surfaces it is subsequently liquified. 
This ingenious proceeding is very ill understood, if it is 
supposed that the aqueous gas carries through the tubes 
where it circulates only the heat that is thermometrically 
sensible: the principal effects are due to the constituent 
heat, the hidden heat, the latent heat, which disengages 
itself at the moment when a contact with cold surfaces 
restores the steam from its gaseous to its fluid state. 
Henceforward, then, we must place heat among the 
constituent principles of the steam of water. Heat is 
obtained only by burning wood or coal; steam therefore 
has a commercial value superior to that of water, by all 
the price of the combustible used in the act of creating 
steam. If the difference of the two values is very great, 
it must be attributed to the latent heat; for the thermo- 
metric or sensible heat has but a small share in it. 
I may perhaps have occasion to enlarge, in the sequel, 
on some other properties of the steam of water. If I do 
not mention them at this moment, it is not that I attribute 
to this assembly the state of mind of certain scholars, who 
said one day to their Professor of Geometry,—“ Why do 
you take so much trouble to demonstrate these theorems ? 
We place entire confidence in you ; give us your word of 
honour that it is true, and nothing more need be said!” 
But it is my duty not to abuse your patience; I have to 
keep in mind also, that by referring to special treatises, 
you can easily fill up the lacune that I have unavoidably 
left. 
