ON OCCULTATION, ETC. 61 



Next to find the coordinates of the moon's centre. 



ifi = No. iVom Table III. to (JJ+6' +2000) 

 = 33-04 

 Then T, /, h and (/ denoting as before, — 



Hence -when 



The quantities x and y are the coordinates of the moon's centre taken in the usual sense, 

 -RÙth the star as origin, and at the times indicated. Nothing is now required but to lay 

 down the moon's position in relation to that of the star, and then obtain the moon's 

 apparent path. 



In the application of the preceding method the following things must be attended 

 to. 



(1.) The moon's motion across the paper is always from right to left. 



(2.) B has the same sign as the declination, i.e., + for north and — for south 

 declination. 



(3.) J is + when the moon is west of the meridian, and — when east. 



(4.) A is + when the moon is moving northwards, and — when moving southwards. 



(5.) ^ is + for north latitude, and — for south. 



The values of .t and y so found are coordinates at intervals of an hour. Coordinates 

 at intervals of one-half hour and thence at intervals of ten minutes are readily found as 

 follows : — 



Let Xi, X.2, x^, denote the three given values of x, and let m be the required term 

 intermediate between x^ and x.,, and n the one intermediate between x., and x^. 



Then 



• ' m = K3-'-'i+C:r.,— X3) =21-58 



n — |(3iC3 4-6X2 — .-c,) = — 3-45 



Similarly for y, 

 . ■ . for 



<= 11" 11" 30'" 12" 12" 30"" 13" 



a; = 34-49 21-58 8-93 —3-45 —15-58 



2/= 3-46 7-72 11-80 15-70 19-42 



