PROCEEDINGS OF THE FOLYTECIINIC ASSOCIATION. 715 



The mode of cometury segregation is different from that vrc have 

 been considering. ' 



The tangential force, aided by heat, being the principal agent, 

 which, moditied by gravitation, gives the comets their extended 

 and extremely elliptical orbits. 



Cometary matter may have been thrown ofi' either from ;he 

 prime soL-u* mass, the primaries, the secondaries, or even from 

 comets themselves. 



The orbits of all the planets are elliptical, and those of the comets 

 exceedingly so. The suu is always in one of the foci of the orbit, 

 and the movement, when m liereJielion, is more rapid than when 

 in aiohelion. 



According to Kepler, the Radius vector of an orbit describes 

 equal areas in equal times. If we suppose the areas of s and .<? to 

 be equal, the body will move from a to b in the same time as from 

 c to d. (See figure.) One comet has been observed to occupy but 

 two hours in passing fvomnode to node, a distance of 1,500,000,000 

 of miles. With so rapid a movement and so quick a curve as that, 

 would not a portion of matter be very likely to go ©ft' upon a tan- 

 gent ? Is it not possible that a small comet performing its round 

 every 33 years gives oft' a little spra}^ at every perihelion passage, 

 thus furnishing us with those beautiful meteoric displays from time 

 to time, of which so much has been said and written ? 



One objection brought against the nebular theory is that it fails 

 to account for the eccentric conrse of Uranus and Neptune, also 

 movem-ents of the moons of Uranus. These may be accounted for, 

 however, by the supposition that the prime nebular mass was not 

 a round and perfect sphere, but was irregular in its contour ; an 

 eccentric and irregular ovoid. The same cause may be assigned 

 for the apparent irregularities, as well as for the eccentricity of all 

 the planetar}^ orbs. 



That finite minds cannot wholly comprehend the modus operandi 

 of some heavenly bodies is no reason for rejecting a theory, which 



