202 THE BORDERLAND OF SCIENCE. 



They cannot have come originally from the sun ; and it 

 is only by entanglement in our system that meteor 

 systems coming from other suns can be compelled to 

 circle around the sun. So that hitherto the theory 

 has been accepted that these meteor systems are actu- 

 ally visitants from interstellar space, which have been 

 entangled by the attraction of some one or other of the 

 planets of the solar system, and so compelled to take 

 up their present paths. 



But it has recently been pointed out that enormous 

 difficulties surround this theory. The giant planets, 

 Neptune, Uranus, Saturn, and Jupiter, undoubtedly 

 have power enough to compel a visitant from inter- 

 planetary space to circle in a closed orbit round the 

 sun, if only the course of the said visitant carries him 

 near enough to the particular giant planet which is to 

 accomplish the work. But the approach must be very 

 close indeed, or else the visitant will not be entreated to 

 stay within our system. The matter is a very simple 

 one. What induces the body to visit our solar system 

 is the sun's attraction. This force acts on the body for 

 millions of years before the body reaches even the 

 outskirts of our system, and in the course of those years 

 the body acquires an enormous velocity sunwards. This 

 velocity would carry it, if undisturbed, close up to the 

 sun, round whose orb the body would swiftly make a 

 half-circular swoop, and would then be carried away 

 by the action of the very same velocity which had 

 brought it close to the sun. If this is to be prevented, 

 it can only be by some planet depriving the body of a 



