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 lacunas that I have unavoidably 

 left. 



