The first stone of this Observatory was laid by Flamstead, on the 10th of August, 1675. It stands 160 feet above low-water mark, and principally consists of two separate buildings: the first contains three rooms on the ground-floor--viz. the transit-room, towards the east, the quadrant-room, towards the west, and the assistant's sitting and calculating-room, in the middle; above which is his bed-room, the latter being furnished with sliding shutters in the roof. In the transit-room is an eight-feet transit-instrument, with an axis of three feet, resting on two piers of stone: this was made by Bird, but has been much improved by Dolland, Troughton, and others. Near it is a curious transit-clock, 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.