Mr. Dalton on the constitution of the atmosphere. 179 



would ascend, especially if the relative weights of their 

 atoms be known. 



For instance ; we know that the diameter of an elastic 

 particle of carbonic acid is nearly, or exactly, the same as that 

 of a particle of hydrogen under the same pressure ; also that 

 their weights are as 20 to 1. At two miles elevation, the 

 elasticity of an atmosphere of carbonic acid gas is diminished 

 one half ; and- at 40 miles elevation, that of hydrogen is 

 diminished one half. Now^ let it be supposed that at 30 miles 

 elevation the carbonic acid atmosphere ceases to exist, or ter- 

 minates, at which elevation its elasticity must be according to 

 the geometrical progression, nearly ^^qqq ; then, by the same 

 law, the elasticity of the hydrogen atmosphere must be 33300 

 at the height of 1 5 x 40 == 600 miles ; also the diameters of 

 the particles of the two gases are still equal at those eleva- 

 tions, because they vary as the cube roots of the elasticities 

 inversely ; that is, if the diameters of the particles of carbonic 

 acid and hydrogen at the surface of the earth be denoted 

 by 1, that of carbonic acid at 30 miles will be represented by 

 ^v/iJooo", and that of hydrogen at 600 miles elevation will 

 also be V 3 3000 . But by hypothesis, this distance is capable 

 of supporting a weight as 20 (namely the weight of one 

 atom of carbonic acid) ; the hydrogen atmosphere therefore 

 must be further elevated till it is capable of supporting a 

 weight only as 1 (namely, the weight of an atom of hydro- 

 gen) ; this will take place when the elasticity is still further 

 diminished in the ratio of the cube of 20 to the cube of 1, or 

 8000 to 1. Hence, we shall have to extend the atmosphere 

 about 13 X 40 = 520 miles further before it can terminate, 

 or to the height of 1 120 miles. In this estimate we have not 



