ON MAPPING THE SURFACE OF THE MOON. 



301 



Notes. 



This Form is intended to aid in the computation of positions of the second 

 order, which are determined, first, by measurements of the angle of position 

 and distance between two points the positions of which have been deter- 

 mined by measurements of the first order (see Beer and Miidler's ' Der Mond,' 

 pp. 40-45), and secondly by the angle of position and the true distance be- 

 tween one of the points of the first order and the point whose position is to 

 be determined. The calculation is performed according to the following 

 formula? : — 



Let AB (fig. 1) be the measured side of a triangle of the first order, I 



