282 
Dr. Brinkley on the 
puted, which in fact is much the same as to recompute the 
index error, 
I know not how far this may have been a source of inac- 
curacy in the north polar distances (p. 388, Phil. Trans. 
1813), from the French refractions. 
They seem to have been merely deduced from the column 
of N. P. D. by Bradley's refraction, and the mean heights 
of the barometer and thermometer, as given in page 386. 
3. As to p, or the effect of parallax, we are not certain that 
many of the standard stars may not have a parallax in de- 
clination, amounting to a fraction of a second. This there- 
fore so far will render the index error uncertain. 
4. As to a , or the effect in declination of the aberration of 
light. 
The maximum of aberration, pretty generally adopted of 
late years by astronomers, is 20", 25. The researches of the 
Chevalier Delambre have principally led to this. The 
maximum formerly used was 20". The former is probably 
more exact, but by no means certainly so. It is even possi- 
ble that the maximum of aberration may be so low as 20", or 
icy', 8. The strongest argument for 24J" is derived from the 
researches of M. Delambre, respecting the reflected light 
from Jupiter’s Satellites ;* which certainly cannot be consi- 
dered conclusive as to the direct light of the stars. 
It seems reasonable to conclude, from an examination of 
Dr. Bradley’s paper on aberration, that this matter requires 
farther examination, and that there is an uncertainty amount- 
ing to a quarter of a second.-f If so, the index error com- 
* Delamb re, Astron. Tom. 3, p. 105 
f See note (A) at the end of this paper. 
