72 OUTLINES OF NATURAL PHILOSOPHY. 



SECT. V. 



Of PARALLAXES. 



HAVING obtained an accurate notion of the figure 

 of the earth, we are enabled to measure the lines 

 either on its surface or in its interior, which must 

 serve as the bases from which, by the rules of tri- 

 gonometry, we are to deduce the distances of ob- 

 jects observed in the heavens. Though the fixed 

 stars are too far off, to have their distances thus 

 ascertained, there maybe others, of which the dis- 

 tances admit of being compared with the diameter 

 of the earth. All distances that are not ascertained 

 by the direct application of a measuring line, are 

 determined on the same general principle; that 

 is, from the change in their angular position, which 

 is made by a known change in the position of the 

 observer. This leads us to consider what is called 

 the Parallax of an Object. 



74. The parallax of any object in the heavens, 

 is the difference of its angular position, as it 



would 



