384 SUN AND MOON FLAT. 



edge, and those which issue from the 

 centre. 



The rays A D and C D appear to be no longer than 

 the ray BD; but if all the rays seem of the same 

 length, the part B will not seem to be nearer to us than 

 A and C, and therefore ABC will look like a flat or 

 straight line. 



The rays AD and C D are 240,000 miles long. 



The ray B D is 238,910 miles long. 



Q. Why do tha STJN and STARS (which are 

 spheres) appear to be FLAT surfaces ? 



A. Because they are such an immense 

 way off, that we can discern no difference 

 of length between the rays which issue 

 from the edge, and those which issue 

 from the centre of these bodies. 



The rays AD and CD appear no longer than B D ; 

 and as B appears to be no nearer than A or C, therefore 

 ABC must all seem equally distant; and ABC will 

 seem a flat or straight line. (See last figure.} 



Q. Why does DISTANCE make an object 

 INVISIBLE ? 



A. Because the angle (made by the 

 perpendicular height of the distant object 

 with our eye) is so very acute, that one 

 line of the angle merges in the other. 



