64 



Instrument for finding the true Lunar Distance. 



is moveable along AE, around the centre O; it is the line of inter- 

 section of the plane of B C with that of A E. The inner curvature 

 of B C, moves in the plane of A E, and along its middle curvature 

 P Q, as the vernier c, travels along AE, and the plane of the arc 

 B C, always passes through the common centre O. 



< 



W 



in the usual manner, for finding longitude from a lunar observation 

 the true distance is determined, hv first mark;™ ^*r ^« «u~ ♦«„« *w* 



