1833.] Attraction and Repulsion. 525 
rapidly ; and, even then, a great part will pass through the cold air 
without mixing with it ; as is plain from the fact, that the hottest air 
in theatres and heated chambers, is near the ceiling, though it re- 
ceives its heat below. Yet, in a mechanical point of view, the vo- 
lumes of air of different temperatures, precisely agree with the differ- 
ent gases ofthe same temperature, mentioned in the supposition, as 
far as having their atoms of different sizes. 
Dr. Tuomson rejects both Mr. Datron’s and BertHou.et’s expla- 
nation of mixed gases. The opinion which he holds, may be brought 
under this head. In his System of Chemistry he states it in the follow- 
ing words: ‘‘ I conceive, that when two gases are mixed, the parti- 
cles of each are beyond the sphere of the affinity of the particles of the 
other. Ifthe elasticity be owing to the action of heat, it seems to. 
follow as a consequence, that different gases must be mutually elastic 
towards each other. But I think that the elasticity itself is sufficient 
to account for this mixture taking place, without being under the ne- 
cessity of having recourse to the hypothesis of Datron*.” 
To this doctrine, I may be permitted to object, that since the atoms 
of any simple homogeneous gas, cannot be supposed continually to 
circulate, if heterogeneous are mutually repellentt, like homogene- 
ous atoms, why should a mixture take place between gases which are 
of the same specific gravity ? But between gases of different specific 
gravity, much less, then, could any mixture take place! Lest it 
should be supposed that difference of gravity in gases may depend 
merely on their ultimate atoms being of different sizes, but of the 
same specific gravity, the atom of oxygen, for instance, being 8 times 
as large as the atom of hydrogen, let it be remembered, that although 
their ultimate atoms might have the same specific gravity, yet when 
endowed, and hence enlarged, with heat, their relative size is greatly 
altered, the atom of hydrogen becomes twice the size of that of oxy- 
gen, and therefore has only th the specific weight. 
There would be no more reason for gases, even of the same specifte 
gravity (supposing such), to undergo a mixture, than for any simple 
homogeneous gas to have circulation among its atoms continually ; 
and still less should gases of different specific gravity mix ; and should 
the latter already be mixed, surely they would in a short time sepa- 
rate. It does not appear then, from all that has been stated, if the 
* System of Chemistry, last Edition, vol. iii. p. 35. 
+ By this expression I mean of course the gases having an effective repulsion 
between them. 
