51 
Dr. Brinkley on the north polar distances , &c. 
Of the recent Catalogues that have been formed of the 
principal fixed stars, two, those of Dublin and Greenwich, 
agree very exactly. That of Mr. Bessel differs considerably ; 
but the differences are such that they would agree by a mo- 
dification of the constants of refraction used. This leads me 
to some considerations respecting the different modes in which 
mv Tables of Refraction, and those of Mr. Bessel, have been 
constructed. I do not venture to decide which Catalogue 
will ultimately be found more correct, that of Dublin, and 
consequently that of Greenwich, or that of Konigsberg. 
Mr. Pond, however, does not admit the agreement of the 
Dublin and Greenwich Catalogues, because we use different 
refractions, and for comparison, takes my column of North 
Polar distances, computed by Bradley’s refractions,* From 
the differences then resulting, he infers a flexure of my in- 
strument. But that such reasoning is inconclusive, will, I 
think, appear from what I shall afterwards state. 
In asserting the general agreement of the Catalogues of 
Dublin and Greenwich, both for 1813 and 1823, 1 mean, they 
agree within certain narrow limits. The mean of the diffe- 
rences of the Catalogues of 1813 is only a few tenths of a 
second. The mean of the differences of the Catalogues of 
1823 is still less. It must therefore at first view appear ex- 
traordinary, that from the comparison of the two Catalogues 
* It ought to be noticed that Mr. Pond, in his paper in the First Part of the 
Philosophical Transactions for 1823, has omitted to state distinctly, that the polar 
distances he reasons on respecting the flexure of the instrument, &c. are not what I 
consider as my polar distances. In one Table, indeed, he puts “ by Bradley’s 
refractions” at the head. But even here a reader might suppose that they were the 
North Polar distances as given by me. In the same Table he places Bessel’s un- 
changed, by the side of mine changed, and compares them together. 
