Calculation of Occult atiom. 161 



Example. 



Log. ta 62^ 2' 0.2749 



V. The logarithmic cosine of this orbital angle added to the 

 proportional logarithm of the hourly motion in declination will 

 give the hourly motion in the orbit, differing but little from the 

 hourly change of longitude. 



Example. Log. cos. 62° 2' 9.6711 



P. L. 1.0858 



P. L. 31' 30",3 0.7569 



We therefore write D*s H. M. 31' 30", S. 62° 2' E. 



vi. It will also be necessary to find the difference of declina- 

 tion at the time of tlie conjunction in right ascension, since this 

 element will be required for the subsequent computation with 

 regard to any particular observation. 



Example. The moon's AR. at 11" is 172° 1' 7",7, that is, 

 3' &',5 beyond the star ; then 



As27'49",3 P.L.A.C. 1892 Again, as 1" P.L. A.C. 5229 

 To 1" P.L. 4771 To6'**42s P.L. 1.4290 



So is 3' 6",5 P.L. 1.7627 So is 14' 46'',4 1.0858 



To 6" 42S 1.4290 To 1' 39" 2.0377 



Now the declination at 11" is 49' 39",4, and consequently 

 at 10" 53^ 18% 51' 18",4, wliich exceeds that of the star, 

 9' 20 ",6 by 41' 57",8, the difference of declination. We there- 

 fore write 1822, Feb. 8, D vSl, 6 \i^ AR. 10" 53" 18% 3)41' 



57",8 N. 



6. Computation of a visible Occultaiion, 



i. Find the moon's altitude for the instant of conjunction in 



right ascension, and for an hour earlier or later, and compute 



the parallactic angle, formed by the circle of declination with 



the vertical circle : this angle subtracted from the polar orbital 



Vol. X. M 



