130 . SEVENTH REPORT—1837. 
is common to all, and each set should give it the same value. This 
is not rigorously the case, and the difference proceeds partly from 
accidental errors in bisecting the star or reading the divisions, 
but still more from causes which are as yet unknown, and whose 
influence is but beginning to be noticed. Lastly, the corrections 
thus obtained must be combined into a general mean according 
to the most probable method, attending to their different weights. 
In some stars nutation appears with a larger coefficient, some 
have been more frequently observed, and both these circum- 
stances must be duly estimated in taking the mean. 
These are my results. To increase Lindenau’s nutation : 
710 observations of y Draconis give + 0-28 
776 —- a Lyre om 20° 54 
705 — « Cygni — + 0°03 
452 a Arcturus — + 0° 33 
369 —_— 6 Urseminoris— + 0° 35 
224 ——— 6 Tauri — + 0°35 
284 —— Aldebaran — +0°31 
2359 ——— a Arietis — +031 
279 —_ a Corone — + 0° 61 
287 ——_ Pollux — + 0°54 
267 ——— Castor — + 0.52 
190 2a a Persei — +0°77 
To diminish it : 
397 observations of » Urs give — 0-29 
403 ——— Capella — —0°31 
393 —— Polaris — —0° 01 
The mean of all being, 
+. 0.1257 
8° 977 
Lindenau = 9-234 
differing only 0-016 from the number selected by Mr. Baily 
for the admirable catalogue which has already been so useful to 
astronomy, and which I trust by the aid of the Association may 
soon be increased far beyond its present extent®. 
It remains to consider what errors may be supposed to affect 
this conclusion. Some may object that I have used with Mr. 
Baily the constant of aberration 20°36, instead of employing 
20°50, which Mr. Richardson has so ably deduced from the 
* Since reading this notice to the Association I have received the Green- 
wich observations for 1836, which enables me to complete the cycle for # 
Cygni, and to determine the proper motions of Castor and Pollux more cor- 
rectly. These, and some other changes of less importance, have slightly changed 
my result, which is now considered by me to be 9°239, 
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