2 Wilde, Origin of Conietary Bodies and Saturn's Rings. 



The more interesting of these nebulse are, M.31 

 Andromedse, M.51 Canum, M.ioo Comae, M 74 Piscium, 

 and many others from which the origin of planetary 

 systems may be inferred with the same degree of pro- 

 bability as in the historical sequences observable in 

 chemistry, geology, biology, or in any other department 

 of the natural sciences. 



That the subsequent condensations of planetary 

 nebulae into spherical bodies would be attended by the 

 evolution of an amount of heat sufficient to make them 

 vividly incandescent, is an obvious conclusion drawn 

 directly from experimental science. It will be further 

 evident that, after the heat of compression had attained 

 its maximum, the self-luminous planets would ultimately 

 become dark bodies through the radiation of their heat 

 into free space. 



It is very generally admitted that the sun, notwith- 

 standing his vast dimensions, would, by continuous loss 

 of heat, ultimately become a dark body like each member 

 of the planetary system. It is also known that the internal 

 parts of the sun are in a gaseous condition and under 

 immense pressure. Some idea of the repulsive force 

 exercised by this pressure may be formed from the 

 ejection of enormous masses of incandescent gas from the 

 surface of the sun to the height of 200,000 miles, with 

 an estimated velocity of 166 miles per second.* 



Assuming the secular cooling of the sun to be continu- 

 ous, the liquefaction and final solidification of his outward 

 parts would follow in natural sequence in accordance with 

 common experience of cooling bodies, while the central 

 parts would remain in their primitive gaseous condition. 

 From strict analogy, it may justly be inferred that all the 

 planetary bodies have gone through the same stages of 



* Young, American Journal of Science, 1 871, p. 468. 



