Proceedings of the Royal Society. 265 
in summer and winter within one-tenth of a second: but, on the 
contrary, that it shews the parallax of « Lyre to be half a second 
greater than that of y Draconis. 
In 1815, the first 15 summer observations, compared with the 
first 13 in November, give a parallax of + 0".72; the next 16 in 
summer, compared with the next 16 in winter, give a negative 
parallax of — 0”.58 ; a comparison which sufficiently proves the 
imperfection of the observations, depending probably on an un- 
steadiness in the instrument. 
In the whole five years the mean of all the observations in 
August exceeds the mean of July by 0".51; a discordance which 
parallax would diminish but in an inconsiderable degree. 
The author pursued a similar train of argument in the second 
part of the inquiry, relating to the absolute parallax of a Lyre. 
While the circle at Dublin, he observes, made from a mean of 
several years the double zenith distance of this star 3” greater 
in the beginning of December than in the beginning of August, 
that of Greenwich shews no difference whatever in the double 
altitude observed by reflection in summer and winter. There are, 
however, differences of above 4 seconds in the difference of alti- 
tude of Lyra and of the Pole-star, as determined in different 
years by the same instrument: and Dr. Brinkley observed, that an 
unsteadiness, amounting to 15” or 20”, is discoverable in the 
comparative results of the different microscopes ; whence he infers 
that there must be an uncertainty, amounting to many tenths of a 
second, in the mean. 
The co-efficients of aberration and of solar nutation, which 
come out 20".35 and 0".51, are certainly true to } or 1; of a 
second, as deduced from the observations of Dublin: the author 
thinks it therefore fair to infer that 1.14, the co-efficient of 
annual parallax for « Lyre, is correct nearly in the same pro- 
portion. Nor are there any changes from season that could pro- 
duce the appearance of regular parallax of all the stars in which 
it has been inferred: and it is very improbable that any error of 
the instrument could have given a parallax to Lyra, and left the 
Pole-star completely free from it. 
