428 Rev. S. Haughton on Mr. G. H. Darwin's Theory 



discrete meteoric stones moving around a solid or liquid 

 nucleus, the difficulty respecting their specifie gravity would 

 disappear. 



3. The recent researches connecting the November, the 

 August, and other periodic swarms of shooting-stars with 

 comets, tend in the direction of showing that comets in cooling 

 break up into discrete solid particles (each no doubt having 

 passed through the liquid condition), and that probably the 

 solar nebula cooled in like manner into separate fiery tears, 

 which soon solidified by radiation into the cold of space. 



4. Mr. Huggins's recent comparisons of the spectroscopic 

 appearances of comets and incandescent portions of meteoric 

 stones, showing the presence in both of hydrocarbon and 

 nitrogen compounds, confirm the conclusions drawn from the 

 identify of the paths of comets and meteoric periodic shooting- 

 stars. 



5. Mr. H. A. Newton, in a remarkable paper read before 

 the Sheffield Meeting of the British Association (1879), 

 showed the possibility (if not probability) of the asteroids 

 being extinct comets, captured and brought into the solar 

 system by the attraction of some one or other of the outer 

 large planets, and permanently confined in the space between 

 Mars and Jupiter, which is the only prison-cell in the solar 

 system large enough to hold permanently such disorderly 

 wanderers. 



In the same paper Professor Newton threw out the idea 

 that some of the satellites of the large planets might also be 

 of cometary origin. 



From all these and other considerations it is therefore 

 allowable to suppose that the earth and moon, when they sepa- 

 rated from the solar nebula, did so as a swarm of solid 

 meteoric stones, each of them having the temperature of 

 interstellar space, i. e. something not much warmer than 

 460° F. below the freezing-point of water. 



Mr. Greorge H. Darwin has shown admirably how the earth- 

 moon s} T stem may have been developed from the time when 

 the earth-moon formed one planet, revolving on its axis in a 

 few hours, to the present time, when the earth and moon (in 

 consequence of tidal friction) have pushed each other asunder 

 to a distance of sixty times the radius of the earth *. 



In his paper on the tidal friction of a planetf (supposed 

 viscous and under the influence of bodily tides caused in 

 it by .an external body such as the moon), Mr. Darwin has 

 found a remarkable equation of condition, which may be thus 



* rroceedibg.s oi' the Koyal Society, l'Jth June, J^7;». 

 t Phil. Trans. 1881, part ii. p. 494^ 



