310 Latitude and Longitude of Yale College Observatory. 
the latitude, by means of the declination circle of a portable Equa- 
torial, the mean of which was about 41° 18’; yet as this circle 
was graduated only to half degrees, and read by means of a ver- 
nier to minutes only, and the mean was derived from but twelve 
observations, this determination might be easily liable to an error 
of half a minute. President Day, assisted by Professor Kingsley, 
observed the solar eclipse of Sept. 17, 1811, with great care, 
and determined therefrom the longitude of the College 4h. 51m. 
50s. This was doubtless a very good observation ; yet as it was 
a solitary observation, and moreover the eclipse was not visible 
in Europe, the longitude deduced might still be erroneous to ten 
or fifteen seconds of time. There was therefore room to hope, 
that by additional observations, greater accuracy might be at- 
tained; and although the results I here present fall far short of 
my wishes, still, as Iam no longer in a situation to prosecute 
them further, I have concluded to publish them. 
The observations for the latitude were made with a sextant 
graduated to 10’, and reading by a vernier to 10”. The mean of 
fifty observations on Polaris made the latitude 41° 19’ 3.9”. The 
mean of thirty observations on southern stars made it 41° 17 
51.1”. Mean of northern and southern stars, 41° 18’ 27.5”. Dif 
ference of the results from northern and southern stars, 1/ 12.8”. 
This difference must arise mainly from the error of graduation. 
I had anticipated such an error from the first, and therefore se- 
lected such southern stars as had about the same altitude with 
the pole-star, in order that all the observations might be made 
upon the same part of the arc. T'o test the instrument, I now 
selected two stars whose places were well known (« Cygni and 
« Bootis,) and from their right ascensions and declinations com- 
puted their angular distance from each other, which distance was 
very nearly equal to the double altitude of Polaris. I then 
watched the opportunity when they were both in the same ver 
tical plane, and when, being on opposite sides of the zenith, the 
whole effect of refraction was to diminish their distance from ea¢ 
other. I made repeated and careful measurements of their dis 
tance on two successive evenings, which made the error of the 
instrument 1’ 11”, being very nearly the difference in the results 
om the northern and southern stars. This difference was not 
owing to index error, which had been carefully measured and al- 
lowed for, but was certainly an error of the graduation, ‘The 
