W. A. Norton—Force of Effective Molecular Action. 487 
pressures, and we may then compute for any supposed value 
of & the volume that should obtain under any supposed pres- 
a ? 
assumed for molecules of oxygen and hydrogen. Taking it 
52r, I have deduced from the hypothesis that ca another 
series of values of the diameter 2A ; and making a new calcula- 
tion, I find the theoretical volume =0°613V. The ratio of 
condensation from the perfect gas in the production of carbon 
dioxide (see p. 485) would lead us to conclude that the diameter 
of the molecule, at the temperature 13°-09 C. would be less 
than 50 (possibly as low as 40). Taking it at 40 I obtain by 
estimation the theoretical volume =0°58V. I have made other 
similar test calculations, with the aid of Dr. Andrews’ experi- 
mental determinations with similar results. 
Lnssae’ the uniform variation of the volume of 
tional to the absolute temperature. e have already seen 
that the elastic pressure of a gas should be proportional to the 
molecular repulsion (F). Now for the range of pressure for 
which the law of Mariotte holds good, we have 
m m' Om 
F =. tf = oS at at 
The volume is represented by 2’*. If a’ becomes x’+dz’, the 
volume becomes (2 +dz’)*=a'*+32'?dz’ (very nearly). Thus 
the increase of volume is 8x’?dz’; and the ratio of increase 
3a’? dx’ 
dead 
But the increment dz’ is due to an increase of tem- 
