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familiar to all, that by the forming of steam, as in common 
evaporation, sensible heat is absorbed, and the air cooled, 
also that when aqueous vapour is condensed, heat is 
given out ; so that heat is thus continually changing 
its form from sensible to latent, and vice versa, by 
the changes of water into the alternate states of liquid 
and vapour. 
The same phenomena, but to a less extent, appears in the 
freezing and thawing of water, namely, when a pound of ice 
is melted in warm water, the amount of sensible heat re- 
quired to convert it into water is about 140° Fahr. more 
than appears in the water, viz,, the heat to maintain its liquid 
form is 140° in excess of what is contained in the state of ice 
at the melting point ; and when the same pound of water is 
again converted into ice it gives out the said 140° of latent 
heat from the liquid in the act of freezing. 
A hundred other cases equally familiar might be adduced 
to show the disappearance and reappearance of sensible heat 
in bodies upon their changes of constituent forms, as solid, 
liquids, and vapours, and in all such cases the increments 
and decrements of heat, in its sensible and latent states, take 
place suddenly, just as the bodies undergo those changes, 
and in strict accordance with known scales of specific heat 
in them, as published in the tables of such heat. 
I may here glance at another aspect of latent heat. We 
have seen that steam of double density, viz., from 251b. to 
501b. per inch, is raised by the addition of 41° of sensible 
heat; and again, from 501b. to 1001b. pressure by the further 
absorption of 46J° of sensible heat. These small accessions 
of heat in its sensible state are accounted for by the amount 
of latent heat in the extra water, as before stated ; for, to 
