C >73 3 
Appendix to Mr. Pond's Paper on Parallax . 
Read March 13, 1817. 
From the month of April 1814, to the present time, the 
observations have been made with two microscopes only, 
and not having this subject in view, they generally are not 
calculated to throw much additional light on this question » 
But last autumn, being induced to suspect, that the discord- 
ance I had met with in favour of parallax, might arise from 
the difference of temperature in summer and winter being in 
an opposite state relatively to the interior and exterior ther- 
mometer, I endeavoured this winter to keep the interior tem- 
perature of the observatory the same as that without, which 
the extreme mildness of the season rendered very easy to 
accomplish. It likewise so happens that from the 1st of 
July last to the present time, the index error of the instru- 
ment has suffered no variation. It may, perhaps, have oscil- 
lated a small fraction of a second on each side the mean, but 
not more ; so that during this interval, the circle may be 
considered as having been a fixed instrument, and therefore 
not liable to any of the objections above stated by Dr. 
Brinkley. Under these circumstances, the observations, 
though not made with six microscopes, are very worthy of 
attention. Those of # Lyrce, 7 Draconis, « Cygni, and a 
Aquilas, are very numerous, and there does not appear the 
least indication of any periodical variation whatever; the 
