Bicxerton.—On the General Problem of Stellar Collision. 185 
motion of translation being originally in the plane of the paper, that ail 
motion but heat motion and original rotation will still tend to occupy that 
plane, and that it is consequently the plane of the rotation of the mass. 
According to the modern theory of heat, all those parts, whose motion of 
mass is destroyed, will have an equivalent heat energy given them. 
Here I approach one of the striking peculiarities of this theory. For 
the temperature developed will not be in any way dependent on the propor- 
tion struck off. It will depend upon the molar velocity destroyed, and this, 
again, chiefly upon the mass of the attracting bodies, and the nearness of 
their centres of gravity. Thus the merest graze will develope nearly as 
high a temperature in the coalesced part as though one half of each were 
struck off. Butin these two cases the gravitating powers of the coalesced 
mass are altogether different, and hence, in some cases, where a small ratio 
is struck off, the molecular velocity may carry every particle away into free 
space, and, in other cases, where the collision is more complete, the great 
attractive powers of the body may hold the gaseous mass in a definite posi- 
tion. I need not refer to the fact that the former case is typical of tempo- 
rary stars, and the latter of nebule of definite form. On reference to fig. 
4, it will be seen that the wounded retreating stars are considerably heated 
in and about the plane of section. On escaping the influence of the other 
bodies they would recover their sphericity, exhibiting a very highly-heated 
part on one side. I hope, in a future paper, to bring before the Institute a 
number of facts and conclusions which, I believe, will actually demonstrate 
that in these bodies we recognize the variable stars which stud our galaxy. 
It is powerful evidence in favour of this theory, that many variable stars 
are in pairs. In figure 5, the arrows show the general tendency of the 
motion in the several parts of the spindle-shaped mass of heated matter. 
I need scarcely mention that the mass in this form is a figure of a large 
number of the characteristic nebule, such as the nebule of Andromeda. 
In figure 6, the rotation of the centre of the mass has begun to give itself a 
spiral form, and an almost exact figure of Herschel’s drawing of the nebule 
of the Lion is produced. The other figures trace the later possible pheno- 
mena which the various motions may produce. They represent systems of 
bodies, spiral, annular, and planetary nebule. I again state, that these 
figures were geometrically drawn on a well-considered estimation of the 
probable residual motion and attractions left in the mass. When some 
discussion has elicited all the difficulties which beset the question, I hope 
to offer you an approximate geometrical demonstration of the problem. I 
believe, however, that it is only in the impact of rare bodies, such as 
nebule, that nebule showing a spiral reaching near the centre could be 
produced 17 
