268 Pleasant Ways in Science. 



Thus, something must move — but what, and how ? The pole 

 star moves so little, or in so small a circle, as to seem the pivot 

 about which the heavens turn, and if all the stars were supposed 

 fixed in crystal spheres, the motions of such spheres would 

 account for very much that is observed. Thus, the ancients 

 for a long time had no notion of the true system. They took 

 the earth for a thing firmly fixed, or rooted, and ascribed all 

 celestial movements to other bodies more or less distant from 

 it. A greater precision of observing power, and a larger store 

 of facts, gradually revealed the real state of the case. 



How do we ever know that we move or are moved, or that 

 anything moves ? In the earth journeys we unconsciously 

 accomplish we have illustrations of motions that carry us along 

 and which we cannot feel. On a dark night, or with eyes shut, 

 in a railway train, a rumbling and shaking informs us that we 

 are not still ; but we easily get confused as to which way we 

 are going, if the motion is smooth enough not to force the fact 

 upon our attention. Our chief evidence that motion has taken 

 place is derived from the information afforded by our eyes that 

 certain things have changed their relative positions. If an 

 object seen one minute on our right, is seen the next minute 

 on our left, either the object has gone half round us, or we 

 have gone half round ourselves. If two objects are situated in 

 front of us, so that when we look straight a-head we can just 

 see both together at the same time, and if a few minutes later 

 we can only see one at a time, either they must have receded 

 from each other, or we must have approached them, so that 

 their actual distance occupies a greater apparent space than it 

 did before. At a distance, the view of a whole town is com- 

 pressed into the size of a sixpence a foot off of our eyes ; nearer, 

 a single brick is more than we can see at once. Let us sup- 

 pose that we see the town in its sixpenny dimensions, and that 

 presently its apparent magnitude far exceeds the capabilities of a 

 single glance. How can we tell whether we have walked to 

 the town, or the town has walked to us ? " What a ridiculous 

 question," would be a general exclamation, and yet how many 

 supposed well educated people could give an intelligible proof 

 of what really occurred ? It would not do for them merely to 

 say that they knew they moved on, because they passed things 

 on the road. We should ask how they knew the things did 

 not pass them. If two bodies are moving in opposite direc- 

 tion, with equal or different velocities, their positions with 

 reference to each other at any given moment will be the same, 

 as if one kept quite still and its motion were added to that of 

 the other, aud in order to prove whether one or both had 

 moved, reference must be made to some fixed and ascertain- 

 able point. 



