172 



LOWELL — SUPPOSED SIGNALS FROM MARS. 



[Dec. 6 r 



and on December 8, 



h = 13.6 miles. 



14. For the calculation of position we proceed ^as follows 



4 % * 







Let 6 = angle which the line from the centre of the phase ellipse 

 to the point upon the terminator perpendicularly under the projec- 

 tion makes with the minor axis of that ellipse. Let r = distance 

 from the centre of the disk to this point. The minor axis has for 

 value r cos £, the major axis being r. By a property of the ellipse 

 we have 



a 2 



tan 8 =_ tan <j> = sec 2 E tan <f> 



