THE STORY-BOOK OF SCIENCE 



our own movement; then we think ourselves immo- 

 bile and fancy we see flying in an opposite direction 

 exterior objects, which are always changing as we 

 look at them. Let the train stop, and immediately 

 trees and houses cease moving, because we no longer 

 have a shifting point of view. A simple carriage 

 drawn by horses, a boat borne along by the current, 

 lend themselves to this same curious illusion. 

 Kvery time we ourselves are gently moved along, 

 we tend, more or less, to lose consciousness of this 

 movement, and surrounding objects, in reality im- 

 mobile, seem to us to move in a contrary direc- 

 tion. " 



' ' Without being able to explain it to myself well, ' ' 

 returned Emile, "I see that it is so. We move and 

 we think we see the other things moving. The fas- 

 ter we go, the faster the other things seem to go. ' ' 



"You hardly suspect, my little friends, that Em- 

 ile 's naive observation leads us straight to one of 

 the truths that science has had the most trouble in 

 getting accepted, not on account of its difficulty, but 

 because of an illusion that has always deceived most 

 people. 



"If men passed their whole life on a railroad, 

 without ever getting out of the car, stopping, or 

 changing speed, they would firmly believe trees and 

 houses to be in motion. Except by profound reflec- 

 tion, of which not everybody is capable, how could it 

 be otherwise, since none would have seen the testi- 

 mony of their eyes contradicted by experience? Of 

 those that have been convinced, one sharper than 

 the others rises and says this: 'You imagine that 



