366 Scientific Proceedings, Royal Dublin Society. 
appear from the Boltzmann-Maxwell Theorem that none such 
would in any appreciable degree be brought into existence by the 
encounters between molecules. If, for example, the expression 
for T contains two B terms instead of 97, then only 2 of the 
energy which is taken account of in the theorem, would be avail- 
able for distribution among 97 distinct kinds of motion, and 
therefore too little for any but a very few of them to be able to 
exhibit an observable effect. The rest, the Bd events, would all 
depend for their activity upon energy reaching the molecules as 
radiant heat or in some other form through the ether, or in some 
other way, as, for example, from a disruption of chemical bonds. 
But though the encounters would be unequal to the task of 
arousing them from a state of quiescence, they, on their side, if 
brought into a state of activity by some other agency may be able 
to impart energy to A and Ba events, which are the proximate 
dynamical cause of the ordinary gaseous laws. This peculiar 
behaviour, whereby energy passes more freely one way than in 
the opposite direction, is a dynamical consequence of the linkage 
between molecules to which Professor FitzGerald has called atten- 
tion. Owing to this linkage the encounters may have to produce 
an effect on a platoon of molecules in order to affect the Bd 
motions of any one of them; and as these encounters are many 
and irregular their aggregate effect can be but small wherever the 
linkage is effective; while, as regards the re-action, the body of 
linked 2 motions act in each encounter on the A or Ba motions of 
a single molecule and may produce a considerable effect on them. 
The dynamical relation is analogous to what would prevail 
between a number of light pellets bombarding a massive body on 
all sides. Their effect on the motion of the massive body is 
small, while its effect on their motions is large. It seems to be 
in this way that radiant heat can warm a gas through the lines in 
its spectrum, very slowly in the more transparent gases, less slowly 
in coloured gases. 
An electron within a molecule may be associated with either 
its Ba or its Bb motions. Thus, when a phosphorescent body has 
been exposed to suitable light, it is an electron associated with Bd 
motions that is primarily acted on by the ether. Now, phospho- 
rescence is a very prevalent property of bodies, inasmuch as it has 
been ascertained by the phosphoroscope that a large proportion of 
