BiCKERTON. — On the Origin of the Solar System, 157 



the centres of the bodies at impact was much greater than the radius of the 

 sun. A considerable distance may be due to two causes — first, the volume 

 of the two bodies ; and, second, the amount of distortion into an egg-shape, 

 at and previous to the impact. The former may be due to rareness, or to 

 great mass. These two actions may have caused the centres to be many 

 times the sun's present radius distant from each other. This distance may 

 be sufficient to bring the original energy required for escape down to a 

 reasonably proper motion. But, explained in anyway, the increased attrac- 

 tion after impact is a serious difficulty in conceiving of the escape of the 

 parts of the original bodies. 



The most serious objection to the suggestion of the planets having been 

 formed from parts of the general mass of the original bodies is that the 

 temperature would be so very high as apparently to prevent such small 

 bodies as the planets being kept together by their mutual gravitation. This 

 action is fully discussed in treating of the origin of planetary nebula. In 

 accounting for planetary nebula with nuclei, the germ of the present dis- 

 cussion will also be found. Planetary nebuls without nuclei may be 

 caused by only outer parts of bodies colhding. Those parts of the original 

 body that come into impact and retain the highest velocity after impact con- 

 sist largely of the matter originally near the centi-e of the original mass. 



Reasons have been advanced for supposing that the centre of bodies con- 

 sists of the heaviest molecules, when the temperature becomes uniform. 

 With such a mass these heavy molecules will, of course, have far less 

 velocity than the light molecules. The escape of these light molecules 

 from the mass will very probably take away a far larger proportion of the 

 total energy than the proportion of their own mass to the total mass, 

 thus leaving the attraction much more effective upon the heavy molecules. 

 Again, when the mass has expanded considerably it may have cooled suffi- 

 ciently to allow chemical union to take place, with the development of still 

 heavier molecules, and certainly a partial destruction of the original mole- 

 cular motion, and a development of atomic motion, which almost certainly 

 gives rise to radiation. Consequently much of the energy of their union will 

 be generally lost as radiant energy. 



The ordinary principles of radiation tell us that the mass, as a whole, 

 also will gradually lose energy during the impact and immediately after. 

 I need not say that I have ah-eady suggested this to account for the 

 extra brilliancy of temporary stars. The formation of these compound 

 molecules would result in a number of small aggregations throughout the 

 mass, and would tend to prevent dissipation into space. 



Thus there are four influences at work which tend to prevent the com- 

 plete dissipation of highly heated masses. 1st. Loss of heat by radiation. 



