485 
the parallax of a. Lyrce. 
to support when the circumstances relative to Aldebaran, 
j3 Tauri, &c. are considered, to which stars I shall presently 
allude. 
Mr. Pond says, “ with respect to the zenith point, his (the 
“ Dublin) instrument, like every one of a similar construe- 
“ tion, is a perfect instrument. No portion of the arc is 
“ employed, nor can temperature have occasioned any error 
“ by its changes. As the star to be examined recedes from 
“ the zenith, the instrument becomes less and less perfect, 
“ and Dr. Brinkley finds a small parallax in a Cygni, a 
“ larger in a. Lyras, and oftentimes a still larger in stars more 
“ remote from the zenith." 
Had the names of the stars which appeared to show, and 
which appeared not to show parallax, been adverted to, this 
argument would have been seen to be of no avail. By a 
reference to my Paper in the Philosophical Transactions, 1821, 
it will be found that I observed, at the opposite seasons, 
Aldebaran, (1 Tauri, u Orionis, Castor, Procyon and Pollux, 
all considerably more distant from the zenith than Lyras. 
All the observations of these stars, in summer, amount to 
above 300, and in winter to nearly 400, and no perceptible 
differences were found at the two seasons. Here tempera- 
ture must have had a much greater effect than with respect 
to u Lyrae. These stars pass late in the evening in winter, 
and near noon in summer, and certainly the difference of 
temperatures is then much greater than between midnight 
in summer and noon in winter. 
But this is only a small part of the force of the argument 
that may be deduced from the observations of these star s. 
