202 Transactions. — Miscellaneous. 



The roughly- spherical nebulae 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 nebulae of 

 definite forms other than spherical, that the peculiarly striking capacity of 

 partial impact to explain phenomena of the heavens becomes apparent. 



The spiral nebulfe have been probably formed by the partial impact of 

 bodies already existing as nebulas before the impact. The forms of the 

 spiral nebulae 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 spkal 

 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 which 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 nebulas occurred, all the difficulties were removed. 

 But it is evident that if spiral nebulas were formed by the impact of nebulae, 

 they would not be found in the galactic ch'cle with the planetary and other 

 nebula of regular shape, but at the galactic poles with the general mass of 

 spherical nebulas. 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 nebula, 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 nebul®, when carefully examined, will be found to be roughly 

 spiral, as Proctor has demonstrated the Universe to be. Probably some of 

 the double nebulae 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 nebixla 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. 



