34»o Dr. Brinkley's observations for investigating 
exactness as to the stability and construction of the transit 
instrument and uniformity of the rate of the clock, is required. 
The Greenwich transit may be considered fully adequate ; 
but it is evident the clock is not so perfect as it ought to be. 
In order to avail ourselves of this method, by stars opposite 
in jR, at first view so plausible, of examining the question of 
parallax, skies much less changeable than those we are ac- 
customed to will be required. As to this observatory, it 
rarely happens that a cloudless sky continues for twenty-four 
hours together. The entire of the observations from which 
my conclusions have been deduced will, I hope, soon be 
published. The particular results, therefore, of part only, 
are here added, that the nature of the observations, and the 
accuracy to be expected from them, may be more fully 
understood. 
In Tables 4 and 5 will be seen the errors of each obser- 
vation of 7i Ursas Majoris and of y Draconis, assuming as 
exact the results of all the observations of each star as to 
the mean zenith distance, parallax, and constant of aber- 
ration. These two stars have been chosen as examples, 
because in these the constants of aberration differ more than 
in other high stars. These stars being so near the zenith 
were observed on the meridian. 
Of the 99 observations of t\ Ur see Majoris. 
18 
79 
In 2 observations the error exceeds 2" 
In 20 observations the error exceeds 1 
I11 79 observations the error is under 1 
99 
