526 On the two great powers, [Ocr. 
repulsion be superior to, and vary in, the same ratio as the attraction, 
that the constitution of mixed gases could be accounted for. 
3. Thirdly, That between gases, the repulsive force is inferior to the 
attraction. 
After having urged the analogy of a solution of a salt in water, Dr. 
Murray observes: ‘‘ It may equally be concluded, that such weak at- 
tractions may be exerted between aeriform bodies,—attractions suf- 
ficient to counteract their elasticity and difference of specific gravity, 
withont being sufficiently energetic to cause an intimate combination. 
And this principle explains the constitution of the atmosphere. An 
attraction of this kind, may be exerted between the particles of oxygen 
and nitrogen gases, may counteract the difference of their specific 
gravities, and prevent them from separating from each other ; and thus 
may be accounted for the two facts, which on former hypotheses ap- 
peared incompatible, the uniformity of the composition of atmospheric 
air, and its having no properties different from those of the gases of 
which it is composed*.”’ 
Under a former headt I have shewn, that the explanation which 
Dr. Murray has given, of a solution of a salt in water is not correct ; 
and therefore the analogy does not hold good between it, as stated, 
anda mixtureof gases. Although the above passage may appear to ac- 
count sufficiently for a mixture of gases, it will not admit of a close 
investigation. It will be easy to shew from their writings, that 
many authors have reasoned, as if attraction and repulsion were supposed 
to vary in the same ratio, though none have expressed a clear and di- 
rect opinion concerning them. 
If then (according to this law{) there exists ‘‘a weak attraction suf- 
ficient to counteract the elasticity’ of gases at any distance, however 
great, it will also be able to counteract the elasticity at any less dis- 
tance, however small ; and hence, of necessity, to bring the atoms of one 
gas into contact with those of the other; before which an intimate 
combination would take place. 
Supposing then the repulsive force, operating between gases, to be 
weaker than their attraction, and to vary in the same ratio with it, the 
mixture of gases could not be explained, since a perfect combination 
would ensue on their being presented to each other. 
* System of Chemistry, vol. ii. p. 41. 
+ ‘‘ The solution of solids in liquids.”’ 
t~ That the two forces vary in the same ratio. 
