210 SEE— RESULTS OF RECENT [April 23, 



tive criticism, except to say that no absolutely conclusive results 

 were obtained until about two years ago, when I recognized from 

 Babinet's criterion that we must unconditionally abandon the his- 

 torical view that the planets have been detached from the sun and 

 the satellites detached from their several planets. This led to the 

 capture theory, which gives us the true conception of the origin 

 of the solar system, and of other cosmical systems existing in space. 



The earliest suggestion of the capture theory runs back a good 

 many years, but it has not heretofore been accepted by professional 

 astronomers familiar with celestial mechanics, because there was no 

 recognized way in which the very circular orbits could be accounted 

 for, except by the detachment theory of Laplace. It is only since 

 the writer's discovery of the paramount part played by the resist- 

 ing medium, some two years ago, that the capture theory has taken 

 a form consistent with the established principles of dynamics. 



As throwing light upon the earliest notice of the capture theory, 

 we may quote a passage from Professor Barnard's article on 

 "Jupiter's Fifth Satellite" in Popular Astronomy, for October, 

 1893, which I came across in making up the engravings for Volume 

 II. of my "Researches" now in press. Barnard says: 



As was the case when Professor Hall discovered the satellites of Mars, 

 many theories have been offered to account for the presence of the new 

 body (Jupiter's fifth satellite). The asteroid zone between Mars and Jupiter 

 is an endless source of material for such theories. It was suggested in 1877 

 that the Martian satellites were asteroids captured by Mars from the asteroid 

 zone lying outside his orbit. These same theorizers have not failed to come 

 up again and suggest that the fifth moon of Jupiter is a captured asteroid 

 from the zone of asteroids lying inside the orbit of Jupiter. They never 

 try to account for satellites of Saturn, Uranus and Neptune this way, because 

 the asteroid mine is too far off; yet they are similar bodies, and undoubtedly 

 had a similar origin. There is no question that this satellite has been there 

 all along, and for infinite ages has been performing its revolutions about the 

 planet, undetected until the night of 1892, September 9. 



This account by Professor Barnard is exceedingly clear, and of 

 great historical interest. It confirms the statement often made 

 that the idea of capture was first entertained by amateurs. The 

 doctrine has grown, however, from the theory of the capture of 

 comets, which has been a subject of investigation by the most emi- 



