92 THE GRAND CENTRE OF THE UNIVERSE. 
track, and the trees get closer together. All this is re- 
versed to one on the engine. The track widens, the 
fences separate, the trees get wider apart as the train 
comes nearer to them. In neither case does he need to 
be told that nothing before, or behind the train is in mo- 
tion, for he knows that the appearances are due to his 
own change of position. Reasoning identical in char- 
acter, leads to the conclusion that the similar, apparent 
motions of the stars are due to a like cause, the rush 
through space of the sun with its train of planets. 
For these reasons astronomers, long ago, came. to. the 
conclusion that the solar system is really moving, but 
positive proof was lacking. This has been supplied by 
the spectroscope. Aided by this instrument, in some 
respects the greatest of all the marvels of science, the 
astronomer can tell whether a luminous body is ap- 
proaching the earth, or receding from it. It is even 
possible to say what the rate of approachis. Now when 
the spectroscope is turned to the heavens, it is found, in 
general, that thestars in the neighborhood of Hercules 
are approaching the earth, while those in the opposite 
part of the heavens are receding from it, exactly the 
effect which would result from solar motion.* It would 
be too absurd to suppose that all the northern stars are 
moving by one system as a river flows by a rock. It-may 
therefore be admitted as beyond all reasonable question, 
that our system isin rapid motion, for it must be rapid 
motion :to.be detected by the spectroscope. Astronomers 
tell us that its rate is probably four miles a second. 
Granted, then, that our system is in motion, the next 
and apparently necessary conclusion is that, somewhere 
in space, is.a vast body, around which our system, prob- 
ably in company with many others, revolves ; and then, 
that this: body, with all its vast retinue of suns and 
* See Newcomb’s Astronomy. 
42 
