197 
1915-16.] Note on Captain Weir’s Azimuth Diagram. 
Applying to it the transformation 
equations (12) readily become 
\-\-x 
x " _i_ _ 2/ 
/_ ' 2 v 
sin 2 b cos 2 b 
1 , 
x'2 y' 2 
x .. . 4- JL = i , 
sin 2 c cos 2 c 
The scale x = — 1, y = cos a becomes x' = 0, y'( = y) = cos a, while the A-scale 
cos A 
(x . = + 1, y = — cos A) goes to infinity. The variable line = — , 
which joins any point A on it to the point x— — l,y = 0, becomes 
y'——x' cos A, a line through the origin cutting the line x' = +1 in the 
scale y' — — cos A. 
We can now construct diagram 5 to be used with parallel rulers which 
bears the same relation to d’Ocagne’s (3.1) nomogram as Captain 
