DETERMINING THE LONGITUDE. 



tables be used, the correction for precession must be found by the rule given 

 in a preceding note. 



Thus, from series first, we obtain the mean of all the right ascensions z= 

 5h. : 36m. : 36s. and of all the declinations 16° : 32. — With these two argu- 

 ments, and the sun's longitude r= 10s : 20°: 30' — enter the tables, and take 

 out the numbers opposite to each, from which are obtained the corrections for 

 precession, aberration, solar and lunar nutation, the Algebraic sum of which 

 is the correction for the apparent right ascension of the stars, whose approxi- 

 mate right ascension is 5 : 3J : 9,5. 99. and declination 16° : 32, and which is 

 found to be 2s. 22. 



This would also be the correction for any one star, whose right ascension 

 and declination were respectively 5h. ; 37 : 26 and 16° : 32'. Proceeding in 

 the same manner with series 2d and 3d, the correction is found to be 2s. 43 for 

 the former, and 2s. 50 for the latter. The labor of finding the corrections for 

 each of the twenty-two stars separately, is thus reduced to three operations. 

 But the labor of computing the corrections for each star, would be greatly 

 diminished, if we possessed tables contaning the maxima of aberration and 

 nutation ; desiderata, which it is the author's intention to supply on the prin- 

 ciple adopted and recommended by Mr. Fallows, in Dr. Pearson's Intro- 

 duction to Practical Astronomy.* 



When the stars observed are to be arranged in series, it will be proper, in 

 the first place, to compute from each star, the approximate ARn. of the moon's 

 limb, in order to detect any error that might inadvertently have been intro- 

 duced in noting the times of transit. The most careful observer is liable to 



* Tlie Tables alluded to, comprehend all the moon culminating stars contained in Pond's 

 Catalogue, and computed for 1835. 



2 P 



