the fixed stars in right ascension. 483 
axis of the ellipse described by parallax should, in the brighest 
stars, amount to o ",5 of space, and not probable that it 
should amount to half this quantity, or to o",25. And when 
we consider that the minor axis of this ellipse is only measured 
in declination (and in a. Aquilse this is only equal to half the 
major axis); and that, moreover, the star is only deranged from 
its mean place, the half of this minor axis, I think it will not 
be very unsafe to conclude, that every attempt to discover the 
existence of parallax by a measure in declination, must end 
in disappointment. 
These observations, continued for many years with the 
transit instrument, must in the end either detect the existence 
of parallax, or still more correctly define its limits. But 
these appear to me even now so small, that I am not dis- 
posed to institute any farther observations with a view to this 
particular subject, but shall leave it to be determined by the 
regular course of observation.* 
• I take this opportunity of stating that the observations of « Cygni, continued in 
the manner described in a former paper, confirm, in the most decided manner, the 
total absence of any observable parallax. They are as follows : 
''gni. 
/3 Ac 
. 
1;° 
irivae. fi 
’S.2 3 
bo 3 
8 <30. 
Difference 
of a. and 
& Cygni. 
Winter, 1817 
Spring, «— 
Summer, — 
Autumn, — 
Winter, 1818 
25 
26 
32 
25 
52 
8,173 
7,920 
3,34° 
4.075 
5.645 
28 
29 
22 
J 7 
47 
„ Sum 
9,818 — i7",984 
10,044 =17 ,964 
14,825 — 18 ,165 
14,067 — 18 ,142 
12,529= 18 ,174 
5,226 
5,287 
5,432 
These observations seem to me to prove beyond a doubt that the parallax of 
a. Cygni cannot much exceed one-tenth of a second of a degree. Vide Phil. Trans, 
1817; 
sR 
MDCCCXVIII. 
