82 Mr. Baily's proposed Tables for the 



rection for such difference may be easily applied. The solar- 

 nutation likewise, depending on twice the same argument as 

 the aberration, may be conveniently added thereto : and the 

 precession, being a constant quantity, and proportional to the 

 time elapsed, may also be easily united to the aberration. It 

 follows therefore that tables of precession, aberration and 

 solar-nutation for each Greenwich star may be so formed, for 

 every tenth day of the year, as to last for many years to come, 

 without the necessity of any other correction than such as 

 arises from the position of the sun on the given day : and the 

 practical astronomer may at any time take out, almost by 

 inspection, the proper quantities required. With respect to 

 ihe lunar-nutation, (to which I shall presently refer,) its value 

 will differ from year to year so considerably, that annual com- 

 putations must be made for each year, and for each star. But, 

 since four computations for each stai', in every year, will be 

 sufficient, they may be so arranged from year to year as to be 

 united with the daily values above alluded to. If Mr. Her- 

 schel's tables, therefore, be considered as the Jirst step to- 

 wards the formation of these daily corrections of the stars, 

 I think that Tables, constructed agreeably to the arrangement 

 here alluded to, may be fairly considered as the second step 

 towards that desirable object. 



3. The subject of the present communication is to point 

 out the best mode of making this arrangement: and in doing 

 this, I must again advert (as I have so frequently done before) 

 to the valuable labours of M. Bessel, who has, in his Funda- 

 menta Astronomice, page 67, shown the principle upon which 

 this arrangement is made. But, as a more detailed explana- 

 tion of it may be acceptable to many of your readers, and 

 may probably lead to a more extensive adoption of it in this 

 country, I hope I need not apologize for the space which 

 I must necessarily occupy for this purpose in your interesting 

 Journal. 



4. Special tables, for determining the apparent places of 

 the Greenwich stars, are generally so constructed as to show 

 the ^losition of the given star at the moment of its culmina- 

 tion: that being the time at which these stars are more usually 

 observed. And this is the method which I shall adopt in the 

 subsequent investigation*. Now, in order to deduce the 

 values of the corrections from one year to another, a Jictitious 

 year must be assumed, commencing at a given epoch ; and 

 consisting of 366 j sidereal days. M. Bessel has assumed the 

 epoch of the sun's mean longitude at mean noon at Paris, on 



* In the Nautical Almanac, however, the apparent places are given for 

 >won. 



January 



