205 
rence of level corresponding to the weight of the vapour con- 
tained in the atmospheric column. No such difference, how- 
ever, could be perceived, the mercury standing at precisely 
the same height in both columns. From all these considera- 
tions, the author infers that the amount of vapour in the at- 
mospheric column is not given by the Hygrometer. 
Passing from the case of vapour to that of gases in general, 
the author adduces certain experiments for the purpose of 
showing that different gases do press upon one another. ‘Thus, 
for example, if a tube filled with phosphorus and cotton be in- 
serted tightly into the neck of a bell-jar filled with water, and 
inverted upon a pneumatic trough, and if the air be admitted 
through an opening in the tube, the air so admitted will be 
deprived of its oxygen before it comes into contact with the 
water. The phosphoric acid being absorbed by the water, the 
pressure on the water in the jar is due only to the tension of 
the nitrogen and carbonic acid present in the atmosphere. If, 
then, oxygen did not press upon these gases, it is plain that 
this tension ought to be less than the atmospheric pressure. 
But as the water stands at the same height in the jar and in 
the trough, it appears that there is no such difference. 
Professor Patton has also accounted for the law of Ma- 
riotte, as applied to mixed gases, by the supposition that ca- 
loric is the force which repels the particles of a gas from each 
other. Admitting the truth of this hypothesis, let p, p’, p” 
be the pressures of three different gases, v, v’, v’ the volumes which 
are subsequently mixed, and n, 7’, n” the numbers of molecules 
contained in the several units of volume. We have then 
p=hkn, p'=kn', p’=kn', 
k being a coefficient depending upon the temperature, and 
therefore the same for all. If now these three gases be mixed 
in a vessel whose volume is V, the number of molecules con- 
tained in a unit of volume of the mixture will be 
on+ vn + vn" 
V 3 
