183 



Appendix to the preceding Paper on the Changes which appear to have 

 taken place in the Declination of some of the fixed Stars. By John 

 Pond, Esq. Astronomer Royal, F.R.S. Read November 14, 1822. 

 [Phil. Trans. 1823, p. 39.] 



The author states that the observations made at Greenwich during 

 the last summer have confirmed his former results, showing most de- 

 cidedly that the computed places of the principal fixed stars do not 

 agree with those determined by actual observation. He finds the 

 general tendency of the deviation to be southward, but inconsiderable 

 in about one third part of the heavens as to right ascension, in which 

 part, from the zenith to the pole, stars appear a very small quantity 

 to the northward ; in the remaining part, as to right ascension, all 

 the stars deviate to the south, and with a few exceptions the south- 

 ern more so than the northern ones. 



He then inquires, whether these deviations admit of explanation 

 by supposing them to arise from errors in the instrument, or in the 

 mode of observing. If occasioned by the general uncertainty of astro- 

 nomical observation, they would be found to follow no law at all ; if by 

 errors in the instrument, they would bear some direct proportion to 

 zenith distance. But these anomalies are shown to depend rather 

 on right ascension than on zenith distance ; and as it cannot be con- 

 ceived in what way error of zenith distance can be influenced by 

 right ascension, the supposition of error in the instrument will not 

 account for the deviations. In further proof of this, numerous ex- 

 amples are given of unequal or opposite deviation in stars adjacent 

 as to polar distance, but of opposite right ascension ; in all which 

 cases, owing to the shortness of the arc to be measured, and the con- 

 stancy therefore of the error affecting it, the deviation of the stars, 

 if owing to the instrument, would be the same both in direction and 

 degree. 



The author next considers the different hypotheses that may be 

 entertained by those who, not convinced by the preceding arguments, 

 may yet be disposed to attribute these discordances to error. Ad- 

 mitting the accuracy of Bradley's observations to form the ground- 

 work of the present inquiry, they must suppose either the Catalogue 

 of 1813, or that of the present period, to be erroneous. If, assuming 

 the present catalogue to be correct, we interpolate between it and 

 that of Dr. Bradley, for the purpose of ascertaining the defects of 

 the Catalogue of 1813, the latter will be found to have been erro- 

 neous beyond belief, and that of Dr. Brinkley, made about the same 

 period, to have been rather more so. It will also follow, from the 

 same admission, that the errors attributable to flexure committed in 

 1813 have since disappeared, and the. instrument has gradually be- 

 come more perfect ; whereas the natural tendency of such a defect 

 would be to increase, and to give receipts every year more and more 

 distant from the truth. 



The validity of the second hypothesis is next examined, which, 

 assuming the Catalogue of 1813 to be correct, regards the present 



