746 Dr. H. Wilde on the Origin of 



confines of the solar system, and that they have, consequently, 

 always been members of it. Moreover, all meteoric bodies, 

 as is 'well known, are mechanical mixtures of elementary 

 substances or their compounds, and further indicate them as 

 the ejectamenta of planetary bodies. 



That comets are planetary ejectamenta, principally from 

 the larger planets, may be justly inferred from the prodigious 

 force manifested by the ejections from other celestial bodies 

 to which attention has already be°n directed. 



The determining cause of the ejection of a comet from any 

 planet would be found in the conjunctive attractions of one 

 or more of their number acting upon that part of the surface 

 from which the cometary matter was ejected. The orbital 

 direction of a comet would be determined solely by the 

 position of the breach in the crust in relation to the orbital 

 motion at the moment of discharge. The motion would be 

 direct when its discharge coincided with the orbital motion 

 of the planet, and retrograde when it was in the opposite 

 direction, as shown in the annexed plate (PI. XIV. fig. 1). 

 And, according as the discharge was more or less at right 

 angles to the plane of the planetary orbit, so would the angular 

 direction of the comet in relation to the ecliptic be determined. 

 The discharge of cometary bodies from vents in high planetary 

 latitudes would necessarily have the greatest inclination to the 

 ecliptic. It may be observed in this connexion that some of 

 the large craters on the moon's surface, and of the terrestrial 

 active volcanoes, Hecla and Mount Erebus, are also in high 

 latitude*. 



To those who are not familiar with the problems of 

 experimental mechanics, it may be of some advantage to 

 demonstrate more fully the direct and retrograde motions of 

 cometary bodies by further illustrations than those shown in 

 my Ha I ley lecture. 



It is common knowledge, based on well-established obser- 

 vations, that the axial and orbital rotations of all the planets 

 are in the same direction, the sun also revolving on its axis 

 in the same direction as the planets. 



As a consequence of the common direction of the axial 

 rotations, the circumferential parts revolve in opposite direc- 

 tions to eacli other, as will be seen in the annexed diagram 

 of the sun and Jupiter (PL XIV. fig. 1). Hence, while the 

 circumferential parts of the planets next to the sun revolve 

 from west to east, the sun apparently revolves from east to 

 west, as is manifest from the motion of the dark spots across 

 the solar disk. 



That the circumferences of moving circles rotate about 



