apparent Places of the Greenwich Stars. 85 



the respective values of the aberration and solar-nutation for 

 each star, on those days, will give the total amount of the 

 correction, depending on those quantities, for each star at the 

 moment of its culmination on every tenth day of the fictitious 

 year, commencing from that moment of time when the sun's 

 mean longitude at mean noon at Greenwich is assumed as 

 exactly 281°. 



9. Having thus deduced the sum of the values of aimual 

 variation, aberration and solar-nutation for each stai-, and for 

 every tenth day of the fictitious year, from January 1 to De- 

 cember 37 * ; they must be arranged into tables, with their 

 differences annexed, and are then ready for use. It is in this 

 manner that M. Bessel has computed and arranged his sub- 

 sidiary tables for the corrections (in right ascension) of 36 

 Greenwich stars, inserted in the Konigsberg Observations for 

 1818; and which may be found in Dr. Pearson's valuable 

 Astronomical Tables, pages 149—152. And it is from those 

 subsidiary tables that M. Schumacher annually computes and 

 publishes his apparent places of the Greenwich stars. It is 

 in this manner also that M. Bessel has computed and ar- 

 ranged the Tables in his Fundamenta Astronomi^e, page 72, 

 for determining the corrections (in right ascension) of 14 prin- 

 cipal Greenwich stars, for the reduction of Bradley's obser- 

 vations. 



10. All these tabular values are computed, as I have al- 

 ready observed, for a Jtctitiaus year (of 366^ sidereal days) 

 which commences from an assumed epoch, depending on a 

 given mean longitude of the sun. But, since the mean longi- 

 tude of the sun at mean noon at Greenwich on January 1, 

 1800, is not exactly 281°; and since it is never the same at 

 the commencement of each civil year, a correction is required 

 for reducing the values, in the proposed tables, to the true 

 epoch, according to the civil mode of reckoning time. And 

 a further correction is likewise required for the longitude of 

 the place of observation ; on the presumption that the pro- 

 posed tables may be used on a different meridian from that 

 of Greenwich. These two corrections are precisely similar 

 to those which I have pointed out in the Introduction to the 

 AV'TU Tables fm- facilitating the computation of Precession, Ab- 

 erration aiid Nutation, alluded to at the commencement of this 

 communication : and therefore it will be unnecessary to dwell 

 further upon them in this place. 



» The year is continued to the fictitious date of December '^1,\n order 

 to conii)letc the decades, and thus facilitate ihu coin()Utatioii of the dif- 

 ferences. For a similar reason the toiiiputation of tlic lunar-nutation is 

 extended to December 07. 



11. There 



