TELESCOPES. SHIPS, 



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Here the tree AD would not be visible to the spec- 

 tator C, even if he were to approach as far as B; 

 because no visible perpendicular can be inserted 

 between the two lines A C, D C, till after the point B is 

 past; when the tree will appear like a very little speck. 



Q. Why do TELESCOPES enable us to SEE 

 objects INVISIBLE to the naked eye ? 



A. Because they concentrate several 

 rays within the tube of the telescope, 

 and bend them upon the mirror or lens y 

 which acts as a magnifying glass. 



Q. When a SHIP ( out at sea) is approaching 

 the shore, why do we SEE the small MASTS before we 

 see the bulky HULL ? 



A. Because the earth is round, and 

 the curve of the sea hides the hull from 

 our eyes, after the tall masts have become 

 visible. 



Here only that part of the ship above the line A C, 



