18*23.] Declination of some of the fixed Stars. 251 



declinations of the stars. Accordingly I found, while collect- 

 ing observations to form a catalogue for the present period, that 

 I could more nearly predict the deviation of a star from its com- 

 puted place, by knowing its right ascension, than its declination. 

 Now it is not easy to conceive in what way the error of au 

 instrument for measuring declination, fixed in the meridian, can 

 be occasioned by any circumstance depending on the right 

 ascension of a star to be observed. 



The general nature of the deviation of the stars from their 

 computed places will be best understood from the annexed 

 tables i'*' in one of which the principal Stars of the Greenwich 

 Catalogue are arranged according to north polar distance, and 

 in the other, in the order of their right ascensions. 



From these tables, it will appear, according to my statement 

 in the former part of this paper, that the general tendency of the 

 deviation is towards the south : that in about one-third part of 

 the heavens in right ascension this southern tendency is very 

 inconsiderable, and would hardly have excited attention ; for in 

 this part, stars between the zenith and the pole, appear a very 

 small quantity to the northward ; whereas in the remaining, and 

 most considerable portion of the heavens, every star appears to , 

 be a considerable quantity to the south of its computed place ; 

 and with few exceptions, the more southward stars have a 

 greater tendency to deviation than the northern ones. 



If we select from the preceding tables those stars which were 

 least frequently observed, at one or all of the three periods, we 

 shall find that they all tend to confirm the foregoing general 

 results ; though they must be regarded as doing so, rather by 

 their united effect, than by their weight of evidence when consi- 

 dered singly. Stars that have been but seldom observed, give 

 results considerably affected by accidental error of observation ; 

 which error is quite of a different nature from that produced by 

 permanent defect in the instrument, and which repetition of 

 observation has no tendency to remove. 



If the deviations of those stars that have been imperfectly 

 observed, were attributable either to error of observation, or 

 defect in the instruments, the deviation would either follow no 

 law at all, or some law depending; upon zenith distance : but the 

 facts we have seen to be at variance with either of these hypo- 

 theses. Not however to rest satisfied with these considerations 

 drawn from the general tendency of all the stars without excep- 

 tion, let us select some striking examples of deviation, in parti- 

 cular groups of stars, on which we might be satisfied to rest the 

 issue of this question. Of these groups I have marked j^ve, in 

 the table of stars arranged according to north-polar distance, 

 each of which we will take the pains to consider more atten- 

 tively. 



J. There are six stars in my Catalogue north of y Draconis, 



* These are necessarily omitted in ^his work : sec note to p. 248, 



