156 Transactions, — Miscellaneous. 



the mutual attraction of the two bodies would be so large a component of 

 the whole, and would always be in one plane, that the orbital planes could 

 not be inclined at any considerable angles to each other. Apparently the 

 next most probable suggestion is the entire escape of the non-colliding parts, 

 and the formation of a spindle-shaped nebula. On investigating the motions 

 of the ends of those spindle-shaped nebulae Avhich must often result from 

 partial impact, it appears that the very unequal velocities of theu' two sides 

 may develope centres of rotation, and these rotating masses from the end of 

 the spindle will be generally the coolest, and composed of the densest 

 elements. They may, therefore, have attractive power enough to keep 

 together, and finally coalesce into planets. 



It is not probable that either one or both of the non-colliding parts 

 passed away from the central mass and returned. There are two reasons 

 against this supposition ; first, it appears very unlikely that the orbits of 

 the planets would be so nearly circular as they are, and, secondly, it 

 appears extremely likely that a double sun would have been formed had 

 this been the case. In both the above suggestions of the origin of the 

 planets the original rotation of the two colliding bodies, and also that of any 

 body revolving around them before the collision, wiU tend to give an 

 irregularity to the plane of the planets' orbits, and also to their axis of 

 rotation ; but the extreme inclination of the axis of Mercury and Venus, and 

 the retrogade motion of Uranus, appear only explicable on the assumption 

 that these bodies were independent satellites existing as such before the 

 impact which gave birth to our system. Further research may, however, 

 show that the original rotation of the colliding bodies may be sufficient to 

 account for all irregularities. 

 Discussion of difficulties that have been met with in working out this theory. 



One of the earliest which presented itself was the possibility of escape of 

 the two original bodies. Many explanations have, however, suggested them- 

 selves, and it is now seen that such escape was non-essential. Any particle 

 situated at the surface of the sun requires a velocity of 378 miles a second 

 to escape the sun. Any mass, no matter how great, supposing its centre 

 were situated at the same position, would require the same velocity. Sup- 

 posing the sun had been formed by partial impact, it would have exerted an 

 additional retarding influence, equal to three-fourths of its mass, upon the 

 two retreating parts, greater than they exerted on each other in approach. 

 The whole of this enormous energy must have been original proper motion. 



Although it is not unlikely that originally the motion of the stars was 

 much faster than at present, yet it is altogether unlikely they had a velocity 

 of 300 miles a second. We must therefore look elsewhere for a solution, 

 and the only one which has at present offered itself is that the distance of 



