THK STAR VAULT. 7 



ouislied. I^et the observer conceive a line drawn in his 

 horizon towards the visible pole. This line may easily be 

 conceived as reaching- the star vault, and, by the rotation of 

 the earth, describing among the stars a circle with radius 

 etjual to the elevation of the pole. All stars within this circle 

 will be manifestly circumpolar. But the elevation of the pole 

 is the latitude of the observer. It follows at once that all 

 stars are circumpolar which are at an angular distance from 

 the pole equal to the latitude of the observer. 



The extreme cases are: — First, that of the pole, latitude 

 90°, where one half of the stars are circumpolar ; and second, 

 that uf the equator, latitude 0°, where none are so. 



The amplitude of a heavenly body is the arc intercepted 

 on the horizon between the east or west point and the meri- 

 dian passing through the body. 



The amplitude of the fixed stars at a given latitude, 

 though affected by precession, is, to all ordinary intents and 

 purposes, a constant ciuantity. I say, to all ordinary intents 

 and purposes, which means that any change supervening is 

 so minute that unless there be special occasion to notice it the 

 change may safely be neglected. There is however, possibil- 

 ity that in the near future we may be addressed by one having 

 authority upon a matter which will include the orientation, as 

 it is called, of Egyptian temples, and alterations in the struc- 

 ture of these from dynasty to dynasty. Both orientation and 

 alteration will be found to have intimate connection with the 

 amplitude of the fixed stars and changes in the same. 



The change, on the contrary, from day to day, of the 

 sun's amplitude at rising and setting, is a phenomenon which 

 can hardly fail to impress itself upon any one in the least 

 accustomed to observe the heavens. 



We shair endeavor to show that the sun can, when in the 

 horizon, have any amplitude between 0° and 90°, according to 

 day and hour and position of the observer. In plainer wcnxls, 



