210 THE BORDERLAND OF SCIENCE. 



produce this particular result ; but every one of the 

 comets or meteor streams known to us should exhibit 

 the peculiarity in question. Now, it is the fact that 

 all the comets which, like Biela's and the comet 

 belonging to the Leonides, have short periods, have 

 their aphelia lying close to the orbits of one or other 

 of the four giant planets. The peculiarity is not now 

 noticed for the first time. It is so marked in the case 

 of the comets dependent on the orbit of Jupiter, that 

 they have been called Jupiter's comet-family. In the 

 case of Neptune, again, there is a less numerous group 

 of the kind, so well marked that, in the plan of their 

 orbits given in Mr. Dunkin's supplement to Lardner's 

 Handbook of Astronomy, the paths appear as though 

 they had been purposely set in symmetrical adjustment 

 with respect to Neptune's orbit. 



Again, we may assume that Jupiter, who exceeds in 

 mass the united mass of Neptune, Uranus, and Saturn, 

 would vomit forth by far the greater number of these 

 mixed masses of 'vaporized and molten matter. It is 

 found, accordingly, that more than two-thirds of the 

 comets which circle in closed orbits around the sun 

 belong to the Jovian family of comets, the remaining 

 third being distributed among the other three giant 

 planets. 



Yet although these circumstances agree satisfactorily 

 with the new theory, they are not altogether con- 

 vincing ; simply because they might be expected to 

 follow if the theory were sound which regards the giant 

 planets as the disturbers of cometic masses arriving 



