158 Mr. Wood house on the derangement of, &c. 
can be partly explained from the fact, that the mean right 
ascensions of the stars having been increased in late cata- 
logues by Mr. Pond, by about o a .3, are greater, by that 
quantity, than in the catalogues from which the solar tables 
are computed. But the differences are very variable ; they 
are greater in summer than in winter. It is far from my 
intention to be cautiously aiming at a merely safe opinion, - 
when I state that, probably, the inequalities of these differ- 
ences arise partly from the errors of the solar tables, and 
partly from instrumental derangement. Certain I am that 
such a derangement, in degree at least, cannot fail to have 
taken place with the transit instrument of this observatory 
when exposed to the sun, and also with the Greenwich 
transit. A derangement of the instrument may also take 
place if a stream of hot, or cold air, should blow partially on 
one brace. 
It is incumbent on me then, at least, to make the experi- 
ment of removing the braces from the Cambridge instrument; 
whether or not the good that will thence result will be more 
than balanced by the evil of depriving the instrument of its 
props or supports in certain positions, is a point which I hope 
soon to ascertain.* 
* It is proper to state, that the fixing of braces to the Cambridge instrument, 
was contrary to the opinion of Mr. Dollond. They were fixed in consequence of 
instructions communicated to him through me (then, with my concurrence) “ to 
make the transit instrument, in all respects, like the Greenwich one.” It is now 
necessary to amend what was done by reason of these instructions, and, probably, 
(for I am anxious to render the instrument perfect by finding out its defects) we 
shall soon have other alterations to make : but if we can change for the better, I 
am sure of the zealous co-operation of Mr. Dollond, who has always been, and 
continues to be, extremely solicitous to render the instrument as perfect as possible. 
