202 Transactions.— Miscellaneous. 
The roughly-spherical nebule are by far the most numerous in the 
heavens, and are chiefly found distributed at the poles of the galactic circle. 
It is probable that most of these, and also many nebulous stars, may have 
been formed by volatilization of bodies passing into heated gas, or by aggre- 
gation, in the manner already described. Some may have been formed by 
impact, either complete or partial. But it is in studying the nebule of 
definite forms other than spherical, that the peculiarly striking capacity of 
partial impact to explain phenomena of the heavens becomes apparent. 
The spiral nebule have been probably formed by the partial impact of 
bodies already existing as nebule before the impact. The forms of the 
spiral nebule were probably at first spindle-shaped, but as the chief part of 
the ends of the spindle would belong each to its respective original body, 
its motion would be directed outward, whilst the inner parts would be in a 
state of rotation. This would gradually convert the whole into a spiral, or 
rather a double spiral. Every gradation from a spindle-shape to a spiral 
are to be found in the heavens; there are spindles showing no signs of 
spiral, some as in Leo, showing the incipient spiral in the centre, and 
others in whieh the spiral is very perfect, and others, again, in which the 
coils of the spiral appear to have passed into a roughly spherical nebula. 
In the earlier discussions on the origin of the forms of these bodies consi- 
derable difficulty was experienced in understanding how a spiral nebula 
could have been formed, as it appeared that the extreme pressure of the 
central mass of the gas must tend to destroy all the spiral structure, espe- 
cially at the centre of the nebula. When, however, the idea of the impact 
of previously-existing nebule occurred, all the difficulties were removed. 
. But it is evident that if spiral nebule were formed by the impact of nebulæ, 
they would not be found in the galactic circle with the planetary and other 
nebule of regular shape, but at the galactic poles with the general mass of 
spherical nebule. On looking upon a celestial globe this will be found to 
be the case. I am aware that much discussion has recently taken place as 
to the existence of these nebule, but it seems almost impossible but that 
some impacts producing them must have taken place, so that not only do I 
believe that their existence will be clearly demonstrated, but that many of 
the spherical nebule, when carefully examined, will be found to be roughly 
spiral, as Proctor has demonstrated the Universe to be. Probably some of 
the double nebule are at present in a state of impact; if so, their form 
ought to alter materially during a single generation. 
I do not imagine that the spindle-shaped nebula is confined to the im- 
pact of rare bodies. It appears to me that all partial impacts will tend to 
produce a spindle-shaped body at first; this matter is fully discussed in a 
paper on the general problem of stellar impact.* The shape may be re- 
* Vide ante. 
