W. A. Norton—Molecular and Cosmical Physics. 9 
on opposite sides of which the number of molecules of the two 
kinds is not the same, the repulsion that takes effect across this 
plane will be of a less intensity than that which is directed 
toward it. 
Since the force of electric attraction that comes into play 
between two dissimilar gaseous molecules, lying on opposite 
sides of the surface of contact, is of the same intensity for 
each molecule, and the molecular repulsion of each gas is the 
same, the velocity of diffusion of ack should be inversely pro- 
portional to the sone root of the density; which is the fun- 
damental law of gaseous diffusion established ‘by Professor 
Graham. In the case ‘of two liquids the result is not precisely 
the same, since the molecular repulsion may be of different 
bet ence the ne forces of 
eee gravity is the least, penetrates most rapidly into the 
other. 
It may be added that the external attraction under considera- 
tion is also the force which gives to liquids their solvent power. 
14. en two substances combine in several different propor- 
tions, the force of affinity is ordinarily weaker in proportion as 
the number of primitive molecules (‘atoms’) of the one that 
i origi with one of the other is greater. This may be ascribed 
the circumstance that each new combination withdraws a 
wage 9 of the electric ether from the sides of the molecules on 
which union has pesos taken place, and occasions a eval 
of the envelopes there. The a of this should generally be 
that the molecular attraction subsisting there is weakened, and 
combined ; or when the decreasing force of external —— 
the envelo s. Thy view of this his sy we may see how it is that 
a minute ¢ e in the proportion of one of the constituents may 
effect a ace change in thes degree of tenacity, hardness, &c., of 
the c poor tne (e. g., different qualities of steel resulting ated 
erences in the quantity of carbon that is combined wi 
the iron). The phenomena of fermentation may be referred ‘ 
e same cause. 
