^0 Sir George Shuckburgh's Account 
consequently subtends an angle of 18". The bisection of 
this last is made use of by day, and although, it is true, it is 
rather larger than is necessary for a meridian point , yet it was 
convenient it should be so, to render it visible in the dark 
winter months, if there was the least vapour rising from the 
ground. Yet with all this, no error need be apprehended ex- 
ceeding 2", equal to only of a second of time, nor that, un- 
less the image should be greatly agitated by the vapours. 
This mark is not only of use to find the meridian, but also 
to determine the horizontal point, when once the angle of it 
above or below the horizon is ascertained ; and, by comparing 
the meridian altitude of any object with this point, its declina- 
tion may be had, almost as nearly as by the level or plumb line. 
I ought to have mentioned before, that the box F is move- 
able upon the plane B,C, by means of an iron frame on 
which it slides, and screws to adjust it finally to the true 
meridian. 
Although there can be no great danger of a solid pier, like 
the above, erected on a foundation four feet deep, being 
likely to move, yet this doubt, if any should occur, may be 
examined by a plumb line a , b, suspended from a, and play- 
ing near a corresponding mark, on the top of a post driven 
into the ground at c. G, E, are steps to ascend to light 
the lamp, or take it in and out at the door d. The whole 
is surrounded by high pallisadoes, to protect it from the acci- 
dents of cattle, or curiosity. 
(20.) Having thus particularly described the various parts 
of the equatorial, I trust in a manner sufficiently intelligible 
to any person a little conversant with astronomical instru- 
ments, it may be proper to say something of its precision ; 
