It will be seen that the result for 1809 agrees with that already fouud to the 

 fourth decimal place. 



Heduction of a and d from any Time t„ to any Time t' by Means of the Precession for the 



Mean Interval. 



Main has given the following expre.s,sions (Mem. R03'. Astron. Soc, XIX. pp. 

 127, 128, 1851), which he has derived from the method printed out by 0. Struve in 

 his " Bestimmung der Constante der Pr£Bcession " (Mem. de I'Acad. Imp. do St. 

 Peter.sburgh, 6th Series, III. p. 49, 1841). 



Let 2hi Ihi P31 Ihf pzi represent the values of the precessions for the times 

 t, It, 3/, 4/, 5^, and let P3, P4, and P5 represent the precessions for the mean 

 intervals. 



Then for the total effect of the precession at the end of any given time i, 

 we have ; 



