■298 Occulta! wns of stars at Madras, [July 



h. m. Moon's a. r. h„ m. Moon's a. 



On 9th Jimeat 11.35 15 57.46.05andat 12.35 16. 0.19.64, 

 Apply the Parallax 0.52.15 — . 1.56.15. 



Apparent A. R,.. .15.56.53.90 15.58.23.49. 



Apparent horary motion 1.29.59. 



On9th Juneat 14. 3 16, 4. 0.97andatl5. 316. 6.35.6L 

 Apply the Parallax —1.13.61 —.2.12.64. 



Apparent A. R... .16. 2.47.36 16. 4.22.97. 



Apparent horary motion 1.35.61. 



Hence we find that in an interval of nearly three 

 hours the variation of the hourly motion is only 6s. ^ 02 

 or 2s. an hour and | of this or Os., 25 is the greatest cor- 

 rection for second differences; hut the Moon's apparent 

 horary motion in right ascension heing ahout l|m. an 

 error of even one second will not alter the predicted 

 time of occultation more than a minute. 



Now to find the times of Immersion and Emersion it 

 only remains for us to determine the apparent place of 

 the Moon and its horary motions, from which, we may 

 compute the two instants when the distance of the cen- 

 tre of the -Moon and star is equal to the semi-diameter 

 of the Moon, thus— 



Find from the Nautical Almanac or any other Ephe- 

 merides the time when the Moon is in conjunction in 

 right ascension with any proposed star together with 

 the difference of declination of the Moon and star at 

 that moment, then compute the corresponding siderial 

 time, the moon's right ascension and declination, and 

 the hourly variation ; then the siderial time — the 

 Moon's right ascension will be = the Moon's hour 

 angle, which will either be + or — as the situation of 

 the Moon is to the west or east of the meridian. 



It is evident that to a spectator on the surface of the 

 Earth the apparent conjunction in right ascension hap- 

 pens sooner than the true as seen from the centre of the 



