Mr. Dalton on the constitution of the atmosphere. 1 79 
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 ; then, by the same 
law, the elasticity of the hydrogen atmosphere must be —g- 
at the height of 15 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 
3 \/ 33000 , and that of hydrogen at 600 miles elevation will 
also be V^ooo . 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 1120 miles. In this estimate we have not 
