parallax of certain fixed stars. 287 
respect to the observations given in the appendix of Mr. 
Pond's first paper. But the knowledge of the stability of the 
index error during six or eight months, depends on the 
reductions by the standard stars ; and therefore the above 
sources of uncertainty remain. Mr. Pond remarks, that 
between July and March the index error may have oscillated 
a small fraction of a second on each side the mean, and not 
more ; so that I think no important conclusion can be deduced 
from the results in that appendix. 
The differences between the exterior and interior tempera- 
ture may have tended to exaggerate the discordance between 
the summer and winter observations made at Greenwich ; 
but it may appear that sufficient observations have not been 
made to ascertain this point, when we consider the many 
other sources of uncertainty. As far as I have examined into 
this matter, with respect to my own observations, I cannot 
suppose any of my discordances materially affected by the 
difference of exterior and interior temperature. The room 
containing the circle at Greenwich is much smaller, and less 
lofty than the room of this Observatory, which contains both 
the circle and transit instrument. 
I hope I have so expressed myself, that I shall be under- 
stood to mean, that I consider the results of observations 
hitherto made by the Greenwich circle inconclusive as to 
the existence or non-existence of parallax, merely from 
the uncertainty of the elements used in the reductions, not 
from any errors of the observations, or from any defects in 
the construction of the instrument. 
I more particularly offer to the consideration of astro- 
nomers the preceding remarks, as in the present state of 
