483 
the parallax of a Lyra. 
The difference of the polar distances of Polaris and a Lyras 
{ an arch of only about 50°) was observed in three successive 
winters ; and the reduction to January 1,1815, will be found 
in Tab. II. The number of observations of each star are quite 
sufficient to obtain an exact result, did not other errors 
than the ordinary errors of observation interfere. These 
observations were made at the same seasons, and therefore 
the effects of different temperatures not likely to appear. 
It may be objected, indeed, that the telescope did not re- 
main in the same position. It remained in the same position 
in 1813 and 1814, but not in 1815; and in 1814 and 1815 
only two microscopes were used. But the result of 1815 
differs 4 seconds from the standard catalogue ; a difference 
far beyond any thing that could arise from errors of division, 
which are thought scarcely to exist in this instrument. 
Mr. Pond appears to consider it of great importance that, 
in the direct and reflected observations of a Lyrae, six micro- 
scopes were used. An inspection of Tab. III. will show an 
extreme unsteadiness in the microscopes when six were used 
in the year 1813, either arising from an unsteadiness in the 
circle, or in themselves. In what way this unsteadiness will 
affect the parallax, it is impossible to conjecture ; but we may 
safely conclude, that where discordances, amounting even to 
15" or 20", take place in the relative position of two micro- 
scopes, that the results, founded on these observations, cannot 
be depended on to a single tenth, or even to many tenths of 
a second. 
I shall now beg leave to make one or two remarks relative 
to the collateral circumstances, which appear to add very 
considerable weight to my explanation by parallax of the 
