CH. XII. 



KEPLEKS ' THREE LAWS: 



97 



between c D and M N. Kepler's telescope is called the 

 ' Astronomical telescope.' It has a much larger 'field of 

 view ' than Galileo's ; that is, it enables you to see over a 

 larger space at one time ; but, on the other hand, it turns 



FIG. 9. 

 V 



Kepler's Telescope. 1 



A u, Object glass, c D, Eye-piece, in n, Real arrow, m' n 1 , Picture of the arrow 

 formed at the focus of the rays. M N, Magnified arrow. 



everything upside down. In making astronomical observa- 

 tions it is not of much importance which part of a star is 

 uppermost ; but for terrestrial telescopes another lens has to 

 be put in to bring the images back to their right positions, 

 and since Kepler's time many other improvements have been 

 made. 



Kepler's first Law, 1609. After Tycho Brahe's death 

 Kepler went on working at the ' Rudolphine Tables,' and 

 this led him to consider again the movements of the planets, 

 and to try and find a theory to explain the path or orbit of 

 the planet Mars. Mars is the planet which stands fourth 

 from the sun ; thus Mercury is nearest to the sun, then 



1 This figure and also fig. 8 were kindly drawn for me by Mr. A. K. 

 Wallace. 



