. Bicxerton.—On the General Problem of Stellar Collision. 183 
This evidence seems to be indisputable. The stars appear to be some- 
thing like the molecules of a heated gas, in motion in all directions, and 
like these necessarily sometimes coming into impact. But many stars will 
come within the effective attraction of other stars, and this attraction will 
be enormously more effectual than mere chance in producing collision. 
Thus the star Alpha Cygni is almost directly approaching our sun, and it 
is extremely likely that in one or two hundred thousand years it will be for 
thousands of years the nearest star, by many times in the heavens, during 
which time, by their mutual attractions, the Sun and this star will probably 
be deflected several diameters towards each other out of their respective 
independent paths. That stars are thus brought within each others’ 
attraction is borne out by the fact observed by Mr. J. W. Wilson, of Rugby, 
that the constituents of the double-star Castor are moving in hyperbolic 
orbits, and it would be well worthy of careful observation to ascertain if 
any other of the binary stars are thus connected. I will not prolong this 
discussion, for it appears certain that cosmical collisions must occur. That 
they do occur on a small scale is evident by the stupendous number of 
meteorites which strike the earth every year, and Proctor’s idea of the small 
craters on the Moon’s surface is that they have been formed by meteors 
falling on its surface during the Moon’s viscous condition; clearly what 
occurs on a small scale, analogy suggests should also occur on a larger 
one. 
Having thus shown that cosmical collisions are necessary events with 
such a system as the galaxy has been proved to be, I shall attempt to show 
that, except in the collision of bodies of very different volumes, complete 
collision is of extreme improbability, or, in bther words, that almost all 
considerable cosmical impacts will be partial collisions. If we suppose 
two bodies of very great mass, and of excessively minute volume, collision 
can only occur when by their motions the two are tending to occupy the 
same point in space at the same time. In most other cases the bodies 
will tend to take hyperbolic orbits with a common focus, hence they 
escape each other. Suppose each to retain the same mass, but the 
volume of each to be expanded beyond the common focus, collision is of 
course inevitable, and it is clear that the impact must be partial. Those 
parts of each which lie in each other’s path will mutually destroy each 
other’s motion, whilst the remainder of each of the two bodies will pass on 
in orbits more curved than before, but which may still be hyperbolic ; or, if 
the original proper motion of the bodies were small, or the part struck off 
of large mass, the new orbits may be elliptical, and one or both of the parts 
will return and remain in permanent orbits, as double stars. I may men- 
tion that I have already demonstrated, I believe, with sufficient clearness, 
