THE ORBIT OF URANUS. 117 



During tlie years 1788-1798 the above systematic difference in right ascension 

 does not appear. The most probable correction seems to be 



Aa = — 0\025 ; A5 = 0".00. 



Whence A long. = — 0". 34 ; A lat. = — 0".10. 



Between the years 1800 and 1823 the stars used for comparison are so widely 

 scattered that I consider it safe to apply only the general mean correction for the 

 epoch 1813, which is 



Aa = — \00r) ; A^ = +0".66. 



Whence A long. = O".0O; A lat. = -|-0 .66. 



From 1825 to 1830 more than half the weight of tlic right ascension comes 

 upon the stars a, (i, and y Acjuila:^, the mean correction to whicli, during this 

 interval, is — 0\035. The general mean correction at this epoch is -)-0\002. I 

 think the right ascensions of these three stars in the Tabulaj liegiomontanaj are 

 really too great at this epoch by tlie entire difference of these results. We may, 

 in fact, hereafter regard the positions of the standard catalogue as sufficiently 

 accurate. The mean corrections to be applied will then be 



A'( = — .017; A^ = +0".83. 



Whence A long. z=r — 0".().j ; A lat. = -|-0".86. 



From the year 1831 until the present time the (ireenwich observations are regu- 

 larly reduced in the several annual volumes of observations. But a reduction of 

 the observations from 1831 to 1835, executed by Mr. Hugh Breen, is given in an 

 appendix to the volume for the year 1864. The results here given differ from 

 those published by Pond in the several annual volumes for the same interval. The 

 right ascensions are altered only by applying the constant correction — 0\030, 

 which is found necessary to reduce Pond's right ascensions to those of the Tabuh^ 

 Regiomontanac. This correction I have verified. The mean correction to reduce 

 the right ascensions of the Tabular Ilegiomontanas to our standard is at this time 

 -[-0\005. On the other hand, when we compare the concluded right ascensions 

 of stars within six hours of Uranus, as given by Pond in the Greenwich observa- 

 tions for 1834, with our standard, we find a mean correction of — ".034 to reduce 

 his positions to the standard, which implies a correction — '.004 to Brccn's reduc- 

 tion. The two results being 4-". 005 and —".004, I have applied no correction 

 whatever. 



In the paper in question the declinations are completely re-reduced, using im- 

 proved data of reduction, but, so far as I see, making no changes in Pond's 

 method. The results differ strikingly from those of Pond, and suggest the 

 desirableness of a complete re-examination of all Pond's determinations of decli- 

 nation. Having no catalogue of observed declinations of standard stars reduced 

 in this same way, we cannot directly determine the systematic correction to the 

 declinations. I therefore proceed as follows: A comparison of Pond's observed 

 declinations of standard stars with Auwers' normal catalogue show that the former 

 require the following corrections near the parallel of Uranus : 



