280 



Di". Tiarks on a Method of reducing 



LVII. An cast/ Method qfrcducins; Sidereal into Mean Time. 



By Dr. T. L. Tiarks.* 

 T^HE following tables are useful to those who, having 

 -^ clocks or time-keepers that show mean time, have fre- 

 quently occasion to calculate the time of transit of stars over 

 the meridian, for reducing observations taken out of the me- 

 ridian, or for ascertaining time by the altitude of a star, &c. 



The right ascension of the star is to be taken from Table III. ; 

 and then, by applying the variation and periodical equations, 

 to be reduced to the day of observation. From this right 

 ascension thus reduced a number is to be subtracted, which is 

 found by Tables I. and IL, the quantity for the next preceding 

 day in 1 able 1. being increased by the quantity corresponding 

 to the number of additional days in Table II., and this sum 



is then -! j. . . , , V by the mean motion of the sun in 

 (^ dmimished J -^ 



right ascension for the longitude of the place of observation 



\ . > of Greenwich. 

 (^ east J 



If this number exceeds the right ascension, 23*' 56' 4"'09 is 



to be added to the latter, or the number is to be calculated 



for the next day, and the right ascension to be increased by 



24 hoiu's. 



Table I. 



* Comrauuicatecl by the Author, 



TABLE 



