Sronsy—Of/ the Kinetic Theory of Gas. 367 
the substances about us are phosphorescent. And although most 
of them, after being stimulated, retain their power of radiating 
light for but the fraction of a second, there are some phosphorescent 
substances in which it lasts for hours. It must be remembered 
that any fraction of a second which the phosphoroscope can detect 
is an immense duration as regards the rapidity of molecular events. 
Accordingly it is with Bb events that we are here dealing. All 
Bb events are sluggish from the molecular standpoint in handing 
over any excess of energy they may possess, either directly or 
indirectly, to the motions of translation of the molecule. But 
viewing the matter from our human standpoint it is convenient to 
distinguish those which can accomplish this in a small fraction of 
a second from those which take so much longer a time that we 
can easily perceive it. We may call the first Bd, events. ‘These 
are they which can effect the transfer through some few millions of 
encounters. And we may call the still more isolated events Bo, 
events. ‘hese latter, for example, manifest their existence when 
phosphorescence lasts for a whole second or more—truly enormous 
durations as regards molecular activities. 
When an electron is associated with Bu events it will promptly 
transfer over any excess of energy it receives from the ether to 
u, v, and w, the translational velocities of the molecule. Accord- 
ingly, on the one hand, the temperature and pressure of the gas 
will increase, and on the other, the etherial undulations that acted 
on the electron will have ceased—in other words, the gas is one 
that has an absorption spectrum. 
If, at the other extreme, the electron is associated with Bc, or 
absolutely isolated events, a beam of light passing through the 
gas will, if it contain certain rays, set these electrons moving. 
They, however, will not impart any of their acquired energy to 
other events going on in the gas, but will continue swinging in 
all the molecules in coincidence with the electro-magnetic wave as 
it sweeps past them in the ether; thus restoring to the latter the 
same amount of energy which they received, and in the form of 
an undulation travelling at the same rate, and in the same direc- 
tion, and oscillating in the same periodic time. Thus, so far as 
regards the motion of this electron, the gas is transparent. 
Between these extremes, electrons associated with Bd events 
will lie, and may produce any intermediate event. 
