Notes on the Theory of Dissociation of Gases. 
By R. Taretrat, B.A., Professor of Physics in the University 
of Sydney. 
[Read before the Royal Society of N.S.W., 1 December, 1886.] 
gases are essentially discontinuous —_ be considered as 
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propose to adopt the following method of discussing the matter. 
eae a molecular theory of any kind, whether of the 
ortex atom, or of the ordinary kinetic type, the temperature 
fica be identified as the mean value of the molecular kinetic 
energy of translation. If the mean mass of a molecule remains 
constant as is generally assumed, then the velocity must increase, 
as the temperature rises—since ot v’ increases. But the pressure 
perature rises as the pressure remains constant, we have to satisfy 
the condition of increasing kinetic energy, pes constant loss of 
momentum per unit area of containing surface. If the mean mass 
remains constant then the number of (merece with the sides of 
the vessel must vary inversely as the mean velocity of the 
molecules ; in other words, the mean free path must increase, 
and we have the phenomenon of expansion. Since in most 
gases the expansion is the same per degree of temperature, the 
increase of the mean free path must be the same. In gases 
which expand abnormally, therefore, either the increase of mean 
free path must be in excess of the normal, or the number of 
molecules in the field must increase. But this increase in’ the 
cate and hence a change of potential energy, while an inerenoed 
free path would occur together with a rise in velocity, if mass be 
