ASTRONOMY* 19 



and is found from this formula, 



,.^ sin d 



cos amplit. = - . 



cos/ 



This is much used in navigation, for ascertaining the 

 variation of the compass. 



28. In those stars which are less distant from 

 the pole than the complement of latitude, the 

 triangle formed by the star, the zenith and the 

 pole, becomes right angled at the star, when 

 the circle described by the star, in its diurnal 

 motion, touches the vertical ; the azimuth is 

 then a maximum, and is found from the solu- 

 tion of a right-angled triangle, in which the hy* 

 pothenuse, the complement of latitude, and one 

 side, the complement of declination, are given, 

 to find the angles, one of which is the azimuth, 

 and the other the horary angle of the star. 



TT . cos Dec. 



Hence sin z = - 



cos Lat. 



, cot Dec. 



and cos h = = 



cot Lat. 



cot Dec. X tan Lat. 



The first of these gives the azimuth when it is great- 

 est, the second the hour when that happens. 

 They are much used for finding the meridian line. 



29. Another 



