1908-9.] 
Motion of Neptune’s Satellite. 
535 
dl 
12. Graphical Solution. — The equation tan ^ = may be 
written in the form 
tan i f/= — 
dl log tan o 
dN 
Plotting the values of log tan - and N as ordinates and abscissae, we 
obtain the following graph, in which the curvature is evident : — 
dl log tan^j 
The values of derived from this graph for the epochs 18740 
and 1890*4 are 1*40 and '94, which are the tangents of the angles J54°*5 and 
43°*2. Comparing these with the values of \Js already calculated, we have : 
1874 - 0 . 1890 * 4 . 
54°*5 43°*2 
52 *6 41 -9 
(Graphic) 
(Calculated) 
