of a Transit Circle. 149 
any deviations in the limb, a quadrant is at the best but an 
imperfect instrument for right ascensions. 
I believe, in the best observatory, I should confine myself 
to a telescope of 4,5 inches, with a circle of about 3 feet 6 
inches. Such a telescope would have great power ; and the 
whole would not be encumbered with too great weight. If 
the telescope be of 5 feet, the circle must be of 4 feet 6 inches 
But I certainly should dissuade the ever going beyond that ; 
and I doubt whether the great additional weight of metal, 
and the disparities there will be in such a mass, would not 
counteract the advantage of a longer telescope. Beside, it 
may deserve consideration, that in a larger instrument some 
parts may be out of the extent of the observer's arms, which 
he could wish to reach. Our late friend, Mr. Smeaton, was 
against a circle of above 3 feet diameter. Between stone piers, 
there must be a double apparatus of microscopes, &c. to use 
when the instrument is reversed. 
In conclusion, it may perhaps be proper to add, since some 
gentlemen may feel inclined to ask, How my instrument lias 
performed ? whether in actual observation it does what was 
expected from it ? To this, I think, I now may fairly answer 
in the affirmative ; that I do find it a very useful instrument, 
and the best adapted, of any that I know, to the perfecting of 
our catalogues. For some time, I will confess, I had my doubts, 
I received it in the beginning of the winter, when the cold 
and dark weather made all examination of it irksome. As a 
transit-instrument, I soon was satisfied with its performance, 
even in respect of the pole star itself. It is very steady ; and 
rarely wants any re-adjustment at all. As a circle, I was not. 
The deviation of the axis, though both ends, as far as I could 
mdccxciii. X 
