7 04 Proceedings of Royal Society of Edinburgh. [sess. 
through space, and a single atom moving rapidly through space. 
The general tendency of subsequent collisions between these rapidly- 
moving triplets and single atoms, with the multitude of slowly-moving 
single atoms throughout space, would he to diminish the energy of 
the intestine commotions of the triplets, and of the motions of the 
centres of inertia, both of the triplets and of the single atoms, 
reducing each triplet to very nearly the condition of equilibrium 
(§16 above) at the corners of an equilateral triangle of side £ with 
a slow translatory motion through space. 
§ 37. By similar dynamical considerations we see that the 
general tendency of collisions between doublets and triplets, or be- 
tween triplets and triplets, must be to form quartets, quintets, and 
sextets of atoms ; and that when such groups, carrying away 
large kinetic energies from the generative collisions, subsequently 
collide with slowly-moving single atoms, the general tendency must 
be to diminish their kinetic energies, and reduce them more and 
more nearly to groups in one or other configuration of equilibrium, 
with slow motion of their centres of inertia through space. 
§ 38. But now consider a collision between a slowly-moving 
triplet or quartet or more-multiple group, and a slowly -moving single 
atom. Even with the triplet the case will not be rare in which the 
single atom will remain in combination, and the result yielded be a 
quartet having considerable intestine commotion, and moving slowly 
through space. In collisions between a quartet and a single atom, 
the case will be relatively less rare, and with a quintet and single 
atom, still less rare for a single atom to remain in combination, and 
form a quintet or a sextet. 
§ 39. If groups of large numbers of atoms in equilibrium, or 
slowly vibrating, have been thus formed, or are given ready formed, 
with single atoms slowly moving in the space all around them, each 
single atom colliding with a group will very frequently remain in 
the group ; and in virtue of the exhaustion of potential energy thus 
effected the vibrational energy of the group will be slightly aug- 
mented. But in not rare cases either the single atom which 
collided, or one of the atoms of the group in the neighbourhood of 
the collision, will be driven off, and generally with much greater 
velocity than the colliding atom had before the collision. Thus the 
average kinetic energy of vibration per atom of the group may be 
