of a Transit Circle. 151 
to be as steady as can well be desired. I had more of these 
dots ; because, the instrument being new, I could not be cer- 
tain in what position it might be found most convenient to 
adjust. I now do it always with the telescope pointing to the 
zenith ; and in another instrument, I should recommend the 
having no more than two dots for that purpose. 
Some small errors I do perceive, which I believe are to be 
ascribed to the great power of my microscopes, which are too 
strong for works of art. It was against the judgment of Mr. 
Cary that they magnified so much ; and I believe he was in 
the right. Some errors are certainly to be laid to the charge 
of my own eyes, which do not define objects as they used to 
do. But in general, I may fairly say, my observations of the 
same star, seldom differ from each other above 5 seconds in 
altitude, and most commonly they are much within that 
limit. 
In observing, I always study to be as much at my ease as 
possible : and therefore I always sit, and use a prismatic eye- 
glass. To avoid touching the instrument itself, or even the 
stone on which it stands, I have four upright poles from the 
floor to the roof, with cross braces on a level with the bottom 
plate of the instrument ; against which I may lean, while I 
observe, or when I handle any part of the instrument. These 
I find to be of great comfort and use. Against two of the 
poles I hang a curtain occasionally, to keep off the sun, or to 
lessen the false light when I observe a star in the day. 
The two exterior horizontal wires, mentioned above, I find 
very convenient. They are really if 43", 5 of a great circle 
distant from the centre. By means of them, I can, without 
any hurry, observe the preceding limb of the sun at 3 wires ; 
X 2 
