Dkeyer — Neio Determination of Constant of Precession. 623 



The correction to Piazzi is + O^'lOO, and that to the Nautical Almanac 

 for 1861-63 is + O^'-OTS : the difference becomes then — 



Schjellerup-Lalande =+ 0^-019 =+ 0"-285. 



This quantity must now be considered as arising from an error in 

 the adopted value of the constant m ; and as the interval between the 

 mean dates of. the two series of observations was found to be exactly 

 66 years, we have for 1829-7 (the mean of the two epochs), 



Am = + 0" -0043. 



This correction has now to be added to the mean of the two values 

 of m which were used for computing the precessions for 1800 and 1865. 

 This is 



m- 46" -06225, 



and consequently the new value is (for 1829-7), 



m = 46" -0666. 



In order from this to determine the Constant of Precession for the 

 epoch 1800, I adopted the values of the planetary precession, the dif- 

 ference between the lunisolar and general precessions, and of the 

 obliquity of the ecliptic, given by the late Professor Peters in his 

 memoir " Numerus constans Nutationis," and found for 1800 + ^ : 



Lunisolar Precession = 50" -3752 - 0" -0002168^. 

 General Precession = 50 -2365 + -0002268 t. 



m = 46 -0581 + -0002849!;. 



w = 20 -0589 - -0000862 t. 



The new value of the Constant of Precession, 50" -2365 for 1800, 

 is only 0" -0046 smaller than the value now in use in all the great 

 astronomical Ephemerides, and the confirmation thus given to Struve's 

 value is of importance, when we remember the uncertain foundation 

 on which the latter rests. That my result is entitled to some weight 

 cannot be doubted, as it depends on more than three thousand stars 

 observed most carefully with an interval of 66 years. The result is 

 also interesting as showing that the fainter stars, down to the ninth 

 magnitude inclusive, are not distinguished by any common and rotatory 

 proper motion, such as would reveal itself by their giving a different 

 value for the Constant of Precession from that given by the brighter 

 stars. 



