410 An Account of the Measurement 
exactly in the true centre of the telescope, the dot on the edge 
of the other limb would have been bisected by the wire of the 
anterior microscope. This was found not to be the case ; but it 
was made to be so, by halving the differences, and moving the 
horizontal wire so as to bisect the mark. After this had been 
again examined, the vertical wire was examined, when it was 
found necessary to go through a part of the operation a second 
time. This was to be expected ; but the wires were, by these 
means, at last properly placed, and guards were then fixed over 
their adjusting-screws. I shall now proceed to speak of the use 
I made of this sector in the year 1802. 
Particulars relating to the Operations of the Tear 1802. 
I have already stated, that a proper observatory had been 
provided for the reception of the zenith sector. The dimensions 
of it were twelve feet square at bottom, and six feet square at 
top; its proportions being the same as those of the external 
stand. A floor having a square vacuity, to admit of the instru- 
ment standing on the ground, covered the joists of it. The sides 
of the observatory were of strong painted canvas ; and the roof 
of wood, with an aperture, which could be opened or closed at 
pleasure, for viewing the stars near the zenith. 
The instrument, with this observatory, was erected in the 
Tower on the 3d of April, merely to examine all its parts, and 
to ascertain whether any thing could be done to render it more 
perfect. Some trifling addenda were accordingly made, and 
the whole, thus rendered perfect, was removed to the Royal 
Observatory, and erected in the garden of the Astronomer 
Royal, close to the eastern extremity of the transit room. 
