1833.] Attraction and Repulsion. 523 
I shall quote the words of this last author, as being concise. ‘‘ The 
repulsion between the particles of any individual gas, is owing to the 
operation of caloric, and is a necessary attribute of the form in which 
it exists; and why should there not be the same repulsion between 
the particles of two bodies in this form ? What cause can counteract 
it, but a chemical attraction exerted between them?” “Besides, if there 
is no repulsion between the particles of different gases, as Mr. 
Daron conceives, what prevents them from entering intocombinations, 
when they approach within short distances, as they must frequently 
do in the internal movements of a mixed elastic fluid ? And if there 
exists no mutual attraction, how are they under any circumstances, as, 
for example, by compression, or elavation of temperature, brought to 
combine? It may be added, that were Mr. Datron’s hypothesis just, 
two elastic fluids ought, in every case, to diffuse themselves in any 
space, and mix equally, with the utmost rapidity, each being as a va- 
cuum to every other. Yet this facility of mixing is much dependent 
on their specific gravity.” In many cases it is very gradual*, 
Mr. Daron afterwards did somewhat modify this doctrine. He 
supposed, that both attraction and the force of repulsion, operate be- 
tween different gases ; but that these forces are so nearly equal, as to 
have no effect in producing the mixturet. 
Many objections against the former doctrine are thus obviated, 
and the spirit of the theory is preserved}. 
_ * Mr. Darron endeavoured to explain this objection away, by an ingenious 
comparison. Page 175. He argues, that, if a ball of lead, which falls throurh the 
air at any given rate, be divided into numerous atoms, it will descend with far less 
velocity (for gravity increases as the cube of the diameter of any sphere, but the 
resistance only as the square of the diameter), and therefore that atoms of air must 
meet with very great resistance ; and hence the slowness of the mixture. This is 
surely not a just comparison ; for the atoms of lead are not resisted merely by ab- 
solute impact against atoms of air themselyes, but by the atmospheres of heat 
round atoms which fill the void space between them, and must be elastic towards 
particles of lead, as towards any other particles. If these atmospheres were re- 
moved, and only the atoms of the air itself remained (they being kept asunder by 
some inherent repulsive force, which in conformity with the theory in question, 
did not operate against the lead), then the lead would probably fall with at 
least equal velocity, by being extremely divided; as its atoms might descend 
unobstructed, the air being almost a vacuum to them ; for its own atoms pro- 
bably do not occupy more than 5,55 of the whole space. For this same reason, 
two gases ought to mix with the utmost rapidity : the actual impacts of their 
atoms themselves being very few. But since they do not mix with such rapidity, 
they cannot be mutually inelastic. 
+ New System of Chemical Philosophy, p. 162. 
+ Let it be however kept in mind, that this theory cannot explain the evapora- 
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