1 8Q3 J Decimation of some of the fixed Stars* %1 



unequal strength of the materials. If we suppose error to exist 

 in each of the catalogues, this cause must have had an opposite 

 influence in the two cases : if we compare the Greenwich obser- 

 vations with those of Dr. Brinkley, we shall arrive at the same 

 conclusion; namely, that the differences must be caused by 

 flexure in one or both of the instruments ; since here also we 

 find that the stars in the neighbourhood of the zenith are affected 

 by only half the difference in polar distance, that is observed in 

 tne stars near the equator ; and the same conclusions may be 

 drawn from comparing the Greenwich observations with those 

 of Mr. Bessel. The polar distances of all the stars in Mr. Bes- 

 sel's catalogue exceed the polar distances given in the Green- 

 wich catalogue ; while those of all the stars in Dr. Brinkley's 

 catalogue as regularly fall short of my determinations. It is not 

 from the casual circumstance of my results being nearly. a mean 

 between the results of those two astronom.ers, that I mtend to 

 claim a superior weight of authority for my own ; for were this 

 the only ground for preference, I should regard the question as 

 yet undetermined, and should think it my duty to recommend 

 the providing of new and more powerful instruments for ascer- 

 taining the truth. But it appears to me that from the observa- 

 tions by reflection, which I have lately made, and from their 

 agreement with my observations by direct vision, that I am 

 entitled to determine the share of error to which each of these 

 two catalogues is liable ; not only from the general superiority 

 of the Greenwich circle, which I consider to have been thus 

 proved, but from this pecuhar circumstance, that whereas in the 

 two catalogues of Mr. Bessel and Dr. Brinkley, the errors can- 

 not fail to be the greatest in stars near the horizon ; by my 

 method of reflection those stars, which are nearest the horizon, 

 must be determined the most correctly, from their double alti*. 

 tudes being measured on the smallest arc. 



In stars near the equator, the catalogue of Mr. Bessel differs 

 from that of Dr. Brinkley five seconds ; and from the preceding 

 considerations, I think we may venture to conclude that Mr^ 

 Bessel's polar distances are too great by about three seconds, 

 and Dr. Brinkley's too small by about two : and since my cata- 

 logue differs from the two former from the zenith to the equator iii 

 very nearly the same proportion, there can be no reason to doubt 

 that their errors throughout are divided in nearly the same ratio. 



With regard to the catalogue for the present period, which 

 accompanies this paper, I beg to state that I consider it only as 

 a very near approximation to the truth, and requiring at least 

 another year's observations, to render it of equal value with Uiat 

 of 1813, vv'hich is the result of two years' observations with six 

 microscopes, and in four positions of the telescope. 



I am persuaded that the more this subject is considered, the 

 more distinctly it will appear, that if any doubt can be enter- 



Neiv Series, vol. vi. s 



