298 FERGUSON'S LECTURES. 



LECT. 



PROBLEM VII. 



A place on the globe being given, and its distance Jrom any 

 other place, to find all the other places upon the globe which 

 are at the same distance Jrom the given place. 



Bring the given place to the brazen meridian, aud 

 screw the quadrant of altitude to the meridian, directly 

 over that place ; then, keeping the globe in that posi- 

 tion, turn the quadrant quite round upon it, and the de- 

 gree of the quadrant that touches the second place, will 

 pass over all the other places which are equally distant 

 with it from the given place. 



This is the same as if one foot of a pair of compasses 

 was set in the given place, and the other foot extended 

 to the second place, whose distance is known ; for if the 

 compasses be then turned round the first place as a cen- 

 ter, the moving foot will go over all those places which 

 are at the same distance with the second from it. 



the length of a degree ot longitude in geographical miles, and hun- 

 dredth parts of a mile, for every degree of latitude, from the equator 

 to the poles : a degree on the equator being 60 geographical miles. 



