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Astronomy. 477 
ture, the evolution of vapor will be continuous until the whole 
mass is converted into it. 
Then comes the question whether a mass of gas or vapor under 
these circumstances would be in a condition of stable equilibrium. 
The analytical discussion of this point leads to the result that, in 
empty and unlimited space, a finite mass of gas is in a condition 
f unstable equilibrium, and must become dissipated by continual 
quence of this result is that the celestial spaces, at least within the 
air upon the surfaces of the celestial bodies and in space. 
stellar system is everywhere filled with atmosp eric air, and tak- 
ing the temperature as that of melting ice, he finds that the lower 
of that of 
limit of density for a portion of gas in space is aise 
becomes still smaller if the temperature of space is taken at —60° 
. with Fourier, or at —142° C. with Pouillet. en 
Any solid body in space must, by virtue of its gravitative 
energy, condense the gas to form an atmosphere upon Its suriace, 
and the density of this gaseous envelope can readily be calculated 
when the size and mass of the body are known. For the m 
the value is found to be ; ao ; of that of the air at the earth’s sur- 
face, a vanishing quantity, and 
the fact that no-trace of a 
spheric influ f : : 
If uid mass, a meteoroid for instance, should exist at a dis- 
tance from the sun or any body capable of radiating heat to it, its 
temperature would be at of the surrounding space, and, if is 
Mass were not too great, a slow evaporation woul nve 
after the lapse of sufficient time into as 
the fiuid mass, on the contrary, approac 
Would occasion a continuous development 
