33 6 Dr. Brinkley’s observations for investigating 
this star seem to render it certain, that my instrument, and 
the mode of proceeding I have adopted, cannot lead to any 
material error. It is evident, that the constant of aberration 
determined by zenith distances of the Pole Star, when ob- 
served above the pole, should be the same as that determined 
from observations of the same star when below the pole. 
The same holds as to the parallax. A comparison of results 
will show the degree of accuracy that may be expected to 
be obtained. Now, by a reference to Table 1 , it appears 
that the constants of aberration only differ by a very small 
fraction of a second, and the results for the parallax agree in 
showing it to be insensible for this star. The passages of 
the Pole Star being separated by twelve hours, the circum- 
stances are in a manner reversed at the opposite seasons of 
the maxima of aberration and parallax. 
The more this argument is considered, the greater weight 
it will, I think, be found to have. The object of our enquiry 
is to ascertain, whether the instrument measures exactly the 
interval between the two places of a star at the opposite 
seasons. We have two modes of doing it for the Pole Star 
under opposite circumstances, and we find the same result. 
It must however be admitted, that it is difficult to ascertain, 
with exactness, the consequences of the differences of external 
and internal temperatures. It is a matter of some importance, 
and I hope to be able to make farther observations for ascer- 
taining, more exactly, its bearing on the present question. In 
the mean time I beg to state distinctly, that, after reviewing 
all the circumstances of my observations, I do not consider 
my conclusions materially affected on this account. 
Mr. Pond mentions, that in winter he endeavoured to 
