52 
Dr. Brinkley on the 
of Greenwich a southern motion is deduced, whereas none 
appears from a comparison of the two Dublin Catalogues ; 
but this is easily explained by an examination of the Cata- 
logues. 
From the weight of external testimony that I shall adduce, 
I think it will readily be conceded to me, that the southern 
motion does not exist. It will follow, therefore, that the 
mean Southern motion must be regarded as an error be- 
longing to one or both of the Greenwich Catalogues of 1813 
and 1823. It may be inferred, that the mean error princi- 
pally belongs to the Catalogue of 1813, as the mean exact- 
ness of the Greenwich Catalogue of 1823 may be inferred 
from its agreement with the Dublin Catalogue of 1823. This 
is the only way it can be inferred. The observations by 
reflection only go to prove a relative exactness ; for, in 
consequence of the Pole Star not having been observed at 
Greenwich by reflection, it was necessary for Mr. Pond to 
assume the latitude of Greenwich, more or less, to accommo- 
date it to the mean error of the Catalogue. 
In my researches relative to the Southern motion, I have 
been able to avail myself of the result of important observa- 
tions by Dr. Bradley, made at Wanstead, in 1728 ; of zenith 
observations made in France, in 1740 ; of Dr. Maskelyne's 
observations at Schehallien, in 1774; of General Mud ge’s 
observations with the zenith sector, in 1802 ; and of General 
Lambton’s zenith distances observed in the Mysore, in 1805. 
All these observations were made with instruments not 
inferior to the zenith sector with which Bradley so exactly 
ascertained the quantity of the aberration of light, and it is 
not necessary for my purpose to suppose them superior. 
