57 
north polar distances of the principal fixed stars. 
In whatever way the subject is considered, the coincidence 
of the Greenwich and Dublin Catalogues speaks in the 
strongest manner for the excellence of the divisions of both 
instruments. 
This coincidence will, if I mistake not, appear in a stronger 
point of view, by deducing the co-latitude of Greenwich from 
applying the zenith distance of each star, as observed by re- 
flection at Greenwich, to the Polar distance of the same star 
as given in the Dublin Catalogue for 1823. The results are 
given in Table 2. The mean of the 30 stars is 38° 31' 20", 8, 
or two tenths of a second less than that assumed by Mr. 
Pond, and four tenths greater than that found by Mr. Bessel, 
from Dr. Bradley’s observations. 
The difficulty that has arisen from the comparison of the 
Greenwich and Dublin Catalogues with that of Mr. Bessel, 
is now to be considered. In this also, there will, I think, be 
nothing found adverse to that degree of accuracy, which is 
supposed to belong to modern instruments and modern ob- 
servations. 
It will readily appear, that the differences between the 
Dublin Catalogue and that of Mr. Bessel, are equivalent to a 
change in the constant of refraction of about one second. If, 
in computing the Dublin observations, we increase my con- 
stant of refraction by half a second, and in computing the 
Konigsberg observations, we decrease Mr. Bessel’s constant 
of refraction by half a second, the Catalogues will be found 
to agree sufficiently. 
It is not necessary to search for other causes till we are 
assured this is not the true one. The investigation of the 
mdcccxxiv. I 
