W. A. Norton—Molecular and Cosmical Physics. 15 
operation is the heat-repulsion—the mutual attractive actions 
the molecular envelopes having become insensible. The 
law of Mariotte may be deduced from this theoretical principle 
in the following manner. Let m be a point in the enclosure 
against which the elastic pressure is exerted, and cmd a slightly 
divergent cone; all the gaseous particles lying within this cone 
will be the centers of heat-waves proceeding in all directions, 
and in the thermal equilibrium of the mass each molecule will 
radiate an amount of heat equal to that which it receives by 
absorption from surrounding molecules. There will acoatiea ae 
be a uniform wave-flow of heat from one layer ab of the 
SS mass to the next toward m, and thus the quantity of 
wave-force that falls on m is the same as if there were an unin- 
terrupted flow directly from one layer ab. Now if the density 
of the gas be doubled, the number of molecules, or wave-centers 
in any layer ab will be oubled, and hence the wave-force 
impinging on m will be doubled. The result is the same as if, 
for every such slightly divergent cone, there was a line of 
aerial particles moving with a certain uniform velocity and im- 
pinging upon m; the density of this representative line being 
proportional to the density of the gas. is dearer idea 
accords with the fndecnatiel hypothesis of the kinetic theory 
of gases. The known deviations from the strict i of the 
proportionality of the elastic pressure to the density 
may be ascribed to the fact that the mutual attractive 
action of the molecular envelopes becomes sensible when 
the density is greatly increased, and the distance be- 
tween the molecules approximates to Od (fig. 4, vol. iui, 
. 889 e well known experiment by Ss oule, which 
established that a gas expanding into a vacuum expe- 
riences no change of temperature, shows that the heat- 
energy lost in the expansion of the escaping gas is 
restored by the impact of the particles upon the enclos- 
as at a should obviously be the result if, as we have 
gaseous phenomena are entirely due to the 
— of “REIS A heat-repulsion, since the energy 
of the repulsive heat-waves expended in imparting 
velocity to the particles should be given out again 
when the motion of the particles is arrest 
It is obvious from the explanation above given of the law 2 
Mariotte that if two different gases have the same temperature 
they will exert the same elastic outward pressure, provided the 
number of their molecules is the same for equal volumes; or, 
in other words, at the same temperature and pressure the num 
ber of ees: es in equal volumes of the two gases should be 
hes sadidie heat of different gases should be the same under 
