12 Wilde, Origin of Covietarv Bodies and Saturn's Rings. 



be retrograde to that of the planet from which it was 

 ejected. 



The orbital velocity of Jupiter being eight miles per 

 second, a body ejected from its interior at a much greater 

 velocity (which I will call the critical velocity) would, by 

 the diminished attraction of the planet, conjointly with 

 the action of solar gravity, revolve with a retrograde 

 motion in an irregular and much enlarged orbit in 

 accordance with the observations {Plate i). And if 

 ejected with a velocity much greater than that necessary 

 to retain it within the sphere of the planet's attraction, 

 the body would move in a separate and elliptical orbit as 

 a comet. 



Considering the comparative minuteness of Jupiter's 

 three outer satellites, which are estimated to be less than 

 thirty miles in diameter, and that the orbits of J VI and 

 J VI I are both inclined at 30" to the plane of the ecliptic, 

 and have nearly the same periodic times and distances, 

 these small bodies are hardly entitled to rank as satellites, 

 but may rightly be regarded as planetary ejectamenta. 

 Nevertheless, the discovery of them is of great importance, 

 as furnishing another indirect proof of the planetary 

 origin of comets. 



Applying the foregoing principles of direct and retro- 

 grade motion of cometary bodies to the explosion of a 

 whole planet between Mars and Jupiter, the fragments 

 projected opposite to the orbital motion would be 

 retarded, and by the action of solar gravity revolve in a 

 smaller orbit than that of the planet before the explosion. 

 On the other hand, the motion of the fragments coincident 

 with the orbital direction would be increased, and by the 

 diminished action of the sun's attraction, revolve in a 

 larger orbit in accordance with the observations. In 

 neither of these cases, however, would the orbits of the 



