constructing a catalogue of fixed stars. 415 
With the mural circle, or any similar instrument, the place of 
a star appears to be defined at the moment of observation with 
much greater precision than by a transit instrument ; but the 
error of the latter, I conceive, to be much more purely 
accidental ; so that the result of a great number of observa- 
tions will be more exact. Local refraction places an insur- 
mountable limit to observations in declination, particularly at 
any sensible distance from the zenith : observations in right 
ascension are free from this material source of error, and are 
therefore susceptible of attaining greater accuracy by con- 
tinued perseverance. 
I have no doubt but to many persons, and even to those 
extremely conversant with the theory of astronomy, it may 
appear, that a very undue degree of importance is attached 
by practical astronomers to the investigation of such minute 
quantities as form the subject of this paper; and it is a 
question often asked, of what importance can it be to science, 
that the place of a fixed star should be so accurately ascer- 
tained ? A person in my situation might reply, that being 
employed to do this, it is incumbent on him to do it in the 
best manner possible, leaving the question of utility to 
others; but there is really a very reasonable and satis- 
factory answer to be given to this question. In the first 
place, since the position of the sun, moon, and planets, are 
deduced from direct comparison with the principal stars, it is 
requisite, for this purpose, that their places should be accurately 
known, and their various changes ascertained. Moreover, 
very good one ; but of all the instruments in the Observatory, it is certainly that In 
which improvement would be most beneficial. 
