CM. XI. 



GALILEO'S TELESCOPE. 



of your glass. But when you do not compare them in this 

 way you do not realise how much the object is enlarged, 

 because it appears to come nearer, so as to be at some 

 point between M N and <?, and consequently to be less 

 magnified I must warn you that both in this diagram and 



FIG. 8. 



Galileo's Telescope. 



A B, Convex Jens ; c D, concave lens next the eye ; m n, real arrow ; M N, apparent 

 size of arrow ; m' in' and ' ', end of the cones of rays m and as they reach 

 the eye ; M o N, angle at which the magnified arrow is seen. 



the one at p. 95 the proportions are very much distorted, 

 because a star or even a house would be an immense dis- 

 tance off as compared with the length of a telescope, where- 

 as, in the drawing, the arrow must be placed as near to the 

 lenses as they are to each other. 



Secondary Light of the Moon. Galileo's first tele- 

 scope only magnified three times, that is, made an object 

 three times larger ; but he made a second which magnified 

 eight times, and then he turned it to the moon and began 

 to examine the surface of that satellite. He saw the moun- 

 tains of the moon, and the deep hollows buried in darkness, 

 and the wide plains which he mistook for oceans. Then he 

 noticed that curious liirht called the secondary light, which 



