4 6 
Mr. Pond on the changes in the 
have found gradually for some time past approaching to those 
results which are obtained at the present day, and which, ac- 
cording to our present hypothesis are supposed to be nearly 
perfect. If the catalogue of 1813 were really so erroneous, 
as our present hypothesis would compel us to regard it, then 
it would appear that Dr. Brinkley’s catalogue for the same 
period must have been still more erroneous, as may be seen 
by inspection of the annexed tables. Now admitting for a 
moment that there were at that time certain imperfections in 
the Greenwich and Dublin instruments, no person will believe 
them to have been so imperfect as our present hypothesis 
would tend to represent them. 
Let us now examine the second hypothesis, which presumes 
the catalogue of 1813 to have been perfect, and consider what 
confidence is due to the Greenwich observations of the pre- 
sent day. This investigation is to be regarded as important, 
not merely with a view to the discussion of the nature of the 
discordances in question, but also from the circumstance, that 
instruments of well-known celebrity are represented as giving 
very different results ; for which reason I shall be excused 
for entering into considerable details on this particular ques- 
tion. As the principal reliance I place on the accuracy of the 
present catalogue, and on the superiority of the Greenwich 
circle over all other instruments, with the history of which I 
am acquainted, is derived from the coincidence of the results 
obtained by the two independent methods ; the one of direct 
measurement of polar distance, the other of observing the 
angular distance of the direct and reflected image of the stars, 
it becomes of some importance to consider in what way this 
coincidence is a proof of the accuracy of either. The source 
