SECT, v.] DISTANCES, HOW FOUND. 49 



finding the absolute distances of the celestial bodies, in miles, 

 is in fact the same with that employed in measuring the dis- 

 tances of terrestrial objects. From the extremities of a known 

 base (N- 115), the angles which the visual rays from the ob- 

 ject form with it are measured ; their sum subtracted from 

 two right angles gives the angle opposite the base ; there- 

 fore, by trigonometry, all the angles and sides of the triangle 

 may be computed consequently the distance of the object 

 is found. The angle under which the base of the triangle 

 is seen from the object is the parallax of that object. It 

 evidently increases and decreases with the distance. There- 

 fore the base must be very great indeed to be visible from 

 the celestial bodies. The globe itself, whose dimensions are 

 obtained by actual admeasurement, furnishes a standard of 

 measures with which we compare the distances, masses,, 

 densities, and volumes, of the sun and planets. 



