478 
Dr . Brinkley’s remarks on 
When, some time ago, in examining the Greenwich ob- 
servations, I found that a comparison of the intercepted arcs 
of the mural circle between Polaris and a Lyrae, in summer 
and winter, gave a parallax for « Lyrae equal to what I had 
found by the College circle, I considered that Mr. Pond’s 
argument from <y Draconis was greatly weakened, and this 
more recent examination has reduced its force comparatively 
to almost nothing. 
An unsteadiness evidently exists in the Greenwich instru- 
ment, and it is impossible to say to what extent it may have 
gone in opposite seasons. Circumstances would lead to the 
supposition that some cause diminishes the measure of the 
intercepted arc between y Draconis and a. Lyrae in winter, 
and so conceals the parallax of a Lyrae. 
The effect of some existing cause of error will appear still 
more plainly if we take an exact mean of all the observations 
in July, made during the five years, and compare them with 
the mean of all the observations in August. 
By 83 days of observation in July - 12 0 53' 56", 33 
63 - - - - - in August 56 ,84. 
Now it is impossible, if there were no cause for the diffe- 
rence of the results obtained under such favourable circum- 
stances, but the ordinary errors of observation, that it should 
have been so great. Parallax being admitted, would only 
do away part of the discordance. Mr. Pond has, in Table XI, 
counted on the agreement of sets of observations less in num- 
ber, and made under less favourable circumstances, to a tenth 
of a second. 
Part of the above difference of half a second in July and 
August, must arise from some change in the measure of the 
