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THE WORLD. 



place, viz : from a to b, due to a real change in the position of 



the spectator. This change, enables us to ascertain the dis- 

 tance of the object with much precision, for supposing A and 

 B joined by a line, we have a triangle ABC, in which one side A 

 B, is known, and all three angles for the observers at A and B 

 determine with some graduated instruments, the inclinations of 

 the lines A c and B c to the line A B. We can illustrate the 

 method by which the distance of an object is ascertained by means 

 of graduated instruments thus : 



Suppose a'spectator at B, to observe by means of a graduated 



