406 THAUMATBOPE. 



sand reflects the rays of the sun like"a 

 mirror. 



Q. If you move a stick (burnt at one end) 

 ROUND pretty briskly, it seems to make a CIRCLE OP 

 FIRE, WHY is this? 



A. Because the eye retains the image 

 of any bright object, after the object itself 

 is withdrawn ; and as the spark of the 

 stick returns before the image has faded 

 from the eye, therefore, it seems to form 

 a complete circle. 



Q. If separate figures (as a man and a horse) 

 be drawn on separate sides of a card, and the card 

 TWISTED quickly, the man seems to be seated on the 

 horse, WHY is this ? 



A. Because the image of the horse 

 remains upon the eye till the man appears. 



The Thaumatrope is constructed on this principle. 



Q. Why do the STARS TWINKLE ? 



A. Fixed stars are so far off, that 

 their rays of light do not strike upon the 

 eye in a continuous flow, but at intervals : 

 when their rays reach the eye, the star 

 becomes visible, and then is obscured till 

 the next batch of rays arrive ; and this 

 perpetually occurring, makes a kind of 

 twinkling. 



