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existence of a limit to vaporization. 
until, by the approximation of their particles, the vapour 
there existing should have an elasticity equal to the force of 
gravity to which it was subject. This is a necessary conse- 
quence of Dr. Wollaston’s argument. 
There is yet another method of diminishing the elasticity 
of vapour, namely, by diminution of temperature. With 
respect to the most elastic substances, as air, and many gases, 
the comparatively small range which we can command 
beneath common temperatures, does nothing more at the 
earth’s surface than diminish in a slight degree their elasti- 
city, though two or three of them, as sulphurous acid and 
chlorine, have been in part condensed into liquids. But 
with respect to innumerable bodies, their tendency to form 
vapour is so small, that at common temperatures the vapour 
produced approximates in rarity to the air upon the limits of 
our atmosphere ; and with these, the power we possess of 
lessening tension by diminution of temperature, may be quite 
sufficient to render it a smaller force than its opponent, gra- 
vity ; in which case it will be easy to comprehend that the 
vapour would give way to the latter, and be entirely condensed. 
The metal, silver, for instance, when violently heated, as on 
charcoal urged by a jet of oxygen, or by the oxy-hydrogen, 
or oxy-alcohol flame, is converted into vapour; lower the 
temperature, and before the metal falls beneath a white heat, 
the tension of the vapour is so far diminished, that its exist- 
ence becomes inappreciable by the most delicate tests. Sup- 
pose, however, that portions are formed, and that vapour of 
a certain tension is produced at that temperature ; it must be 
astonishingly diminished by the time the metal has sunk to a 
mere red heat ; and we can hardly conceive it possible, I think, 
