10 OUTLINES OF NATURAL PHILOSOPHY. 



&. If the meridian altitude of the star is less than 

 that of the equator, its declination is on the oppo- 

 site side of the equator from the zenith of the place, 

 otherwise on the same. 



Thus the places of the stars, as north or south of a 

 given plane, that of the equator, are determined ; 

 but those places, to be fully known, must be deter- 

 mined in the direction of east and west, in respect 

 of a given circle at right angles to the equator. 

 Now, of the circles at right angles to the equator, 

 or the circles of declination, no one is fixed in its 

 position, but all of them revolve uniformly with 

 the heavens ; so that it is only by the computatipn 

 of time that one of them can be distinguished from 

 another. 



The circle of declination which passes through the 

 point in the equator which the sun occupies at the 

 vernal equinox, has some advantages above the 

 rest, as a line to which the stars are to be referred. 

 Jt is called the Equinoctial Colure, and its position, 

 with respect to the meridian of a given place, for 

 a given instant, may be determined by means of a 

 clock, regulated according to the following me- 

 thod. 



17. The time from a star being on the meri- 

 dian, to its next coming to the meridian, is al- 

 ways of the same length ; it is called a Siderial 

 Day. 



The 



