818 



OPTICS. 



the lanthorn and the spectator. The appearance 

 of the image approaching and receding is owing 

 simply to removing the lanthorn farther from the 

 screen or bringing it nearer to it : for the size of 

 the image must increase, as the lanthorn is carried 

 back, because the rays come in the form of a cone; 

 and, as no part of the screen can be seen, the 

 figure appears to be formed in the air ; to move 

 farther off when it becomes smaller, and to come 

 nearer as it increases in size, though, in reality, it 

 is still at the same distance. 



