Broxerton.—On Temporary and Variable Stars. 121 
the influence of each other's gravitation, they would be attracted out of 
their path with a constantly increasing velocity. Three possibilities present 
themselves: the first, the most general one, of passing each other and 
ultimately attaining their original velocity in space; the second would 
be that of imperfect impact; and third, as an extreme case, we 
should have complete impact when the centre of each mass would have, 
except for the collision, occupied the same point at the same time. It is 
reasonable to assume that in impact the case of partial collision would be 
more probable than complete impact. And it is this imperfect impact that 
is the basis of the present hypothesis. In this case a piece will be struck 
off each colliding body; these two pieces would to a greater or less degree 
coalesce, developing at the same time a high degree of heat, whilst the 
remainder of the two bodies would pass on in space. What would finally 
happen to the two retreating bodies depends on the original proper motion 
and the masses of the coalesced piece. If the original proper motions were 
large and the piece cut off small, one or both of the two bodies would most 
likely pass entirely away from the other bodies and travel on independently 
in space. If, on the other hand, the original proper motion were small and 
the piece struck off large, then it would be most probable that they would 
be once more attracted back and collide again and again until complete 
coalescence took place; or, as I shall show further, it is possible that they 
may form a system similar to our solar system. The size of the bodies will 
also have an influence in the escape or otherwise of the pieces. Other 
things being equal, the larger the body the greater the probability of escape, 
as the distance between the centres will be greater and consequently the 
attraction will be less. 
Partial impact appears competent to explain the occurrence of temporary, 
double, and variable stars, nebule of various kinds (the kind depending on 
the nature of the impact), comets, and finally stars or suns accompanied by 
bodies of smaller size. The third case, that of complete coalescence, is pro- 
bable only in the collision of very large bodies, and offers an explanation of 
the existence of large spherical nebule with a general condensation towards 
the centre. (We will consider the hypotheses somewhat in detail.) In 
order to render the conception of the hypothesis as simple as possible, I 
shall all through keep as far as I can to a direct conception of energy, as in 
this way most questions may be reduced to ordinary arithmetical series, 
Thus, if the two approaching bodies be equal to each other (at the same 
distance), the attracting force acting on each unit of mass will be propor- 
tional to the total mass of either; now in a force acting through space, the 
work equals the force multiplied by the space through which it acts, and the — 
work is equal to the heat, A 
