860 Mr, Pottd OH the Changes in th€ [Oct. 



Article III. 



Appendix to the preceding Paper on the Changes which appear to 

 have taken place in the Declination of some of the jixed Stars. 

 By J. Pond, Esq. Astron. Royal, FRiS. Read Nov. 14, 1 822.* 



The observations which have been made during the last 

 summer, confirm in a very decided manner the results which 

 formed the subject of my last communication ; in which I laid 

 before the Society the nature of the differences that exist 

 between the computed places of the principal Stars of the 

 Greenwich Catalogue, and those deduced from actual observa- 

 tion. It is not my present intention to offer any explanation of 

 the cause of these pheenomena, although many obvious conjec- 

 tures present themselves, the value of which it will require per- 

 haps many years to determine. It is now my principal object 

 to consider the force of that explanation of the differences in 

 question, which will most readily occur to every astronomer, 

 namely, that the whole may arise either from error committed by 

 the observer, or from defect in the instruments of observation : 

 this objection being the more weighty from the circumstance, 

 that the observations of three distant periods are employed, and 

 that an errorin those of either period (but particularly of the two 

 latter) would materially affect the result now under conside- 

 ration. 



1 believe that every person, in proportion to his experience in 

 the use of astronomical instruments (even of the most unexcep- 

 tionable construction), will be cautious in admitting the accu- 

 racy of any results, with whatever care the observations may 

 have been made, which appear to militate against any received 

 theory of astronomy ; and 1 shall have occasion myself to show, 

 from the great discordances between instruments of the highest 

 reputation, that this distrust is but too well founded. More 

 particularly ought our suspicion to be excited, when such ano- 

 malies are found to exist, as bear some direct proportion to the 

 zenith distances of the stars observed. In all such cases we 

 should never hesitate, I think, to ascribe the anomalies to defec- 

 tive observation. If therefore in the present instance, any part 

 of the discordances in question can be shown to depend on polar 

 or zenith distances, I shall wilhngly admit, as to such part of 

 them at least, that they are no otherwise of importance, than as 

 affording data for leading to the detection of some hitherto 

 undiscovered errors. The anomalies, however, that have led me 

 on to this inquiry, and to which alone I attach any importance, 

 are found to depend rather on the right ascensions, than on the 



• From the Philoeophical Transactions for 1823, Part I. 



