54 
Dr. Brinkley on the 
shall here confine myself to the consideration of the North 
Polar distances, and as connected therewith of the Southern 
motion. 
On the Catalogues of North Polar Dista?ices. 
I have placed, in Table I., beside each other, the North 
Polar distances observed at Greenwich about 1813, and at 
Dublin about the same time, together with the differences. 
In like manner have been placed also the Greenwich and 
Dublin North Polar distances of 1823, together with the 
differences. An inspection of these will show, except in 
one or two instances, a very extraordinary agreement. Many 
of the Polar distances differ by less than 1 " ; and with the 
exception of Sirius, in the Catalogue of 1813, the differences 
are never greater than what might arise from accidental 
circumstances. The Greenwich Catalogue of 1813 is less in 
its mean quantity than that of Dublin by o",47, and the 
Greenwich Catalogue of 1823 is greater than that of Dublin 
in its mean quantity by o",io. But we are to consider that 
these Catalogues are computed by different tables of refrac- 
tion. The constant of refraction (p—r!) in Bradley’s table 
(that used by Mr. Pond) is 57". In my Table it is 57", 72. 
My constant has been determined by the circle and the 
meteorological instruments used here, and therefore must 
necessarily be adopted for my observations. When an as- 
tronomer has found the constant of refraction by his own 
instruments, his Catalogue of North Polar distances ought to 
be formed independently of any other instrument or table of 
refractions. No partial change can be admitted. Mr. Pond, 
