made by Graham, but greatly improved by Earnshaw, who so simplified the
train as to exclude two or three wheels, and also added cross-braces to
the gridiron-pendulum, by which an error of a second per day, arising
from its sudden starts, was corrected. The quadrant-room has a stone
pier in the middle, running north and south, having on its east face a
mural-quadrant, of eight feet radius, made by Bird, in 1749, by which
observations are made on the southern quarter of the meridian, through
an opening in the roof three feet wide, produced by means of two sliding
shutters; on its west face is another eight-feet mural quadrant, with an
iron frame, and an arch of brass, made by Graham, in 1725: this is
applied to the north quarter of the meridian. In the same apartment is
the famous zenith-sector, twelve feet in length, with which Dr. Bradley,
at Wanstead, and at Kew, made those observations which led to the
discovery of the aberration and nutation: here also is Dr. Hooke's
reflecting telescope, and three telescopes by Harrison. On the south
side of this room is a small building, for observing the eclipses of
Jupiter's satellites, occultations, &c., with sliding shutters at the
roof and sides, to view any portion of the hemisphere, from the prime
verticle down to the southern horizon: this contains a forty-inch
achromatic, by the inventor, Mr. John Dolland, with a triple
object-glass, a most perfect instrument of its kind; and a five-feet
achromatic, by John and Peter Dolland, his sons. Here, likewise, are a
two-feet reflecting-telescope (the metals of which were ground by the
Rev. Mr. Edwards), and a six-feet reflector, by Dr. Herschell.

The lower part of the house serves merely for a habitation; but above is
a large octagonal room, which, being now seldom wanted for astronomical
purposes, is used as a repository for such instruments as are too large
to be generally employed in the apartments first described, or for old
instruments, which modern improvements have superseded. Among the former