importance to have an easy and accurate method of finding the longitude at sea. A plan was proposed, founded upon the principle now in use, of observing the lunar motions and distances during a voyage, and comparing them with a previous home calculation, thus ascertaining the difference between home time and time at sea, from whence the difference of longitude is readily deduced. A reward being sought by the proposer from the government of Charles II. it was referred to a commission to report upon the merits of the scheme. Flamstead, one of the commissioners, at once decided against its practical utility, on the ground of the inaccuracy both of the lunar tables and of the positions of the stars in existing catalogues, which only a lengthened course of observation could rectify. The king, declaring that his pilots and sailors should not want such assistance, immediately instituted the office of astronomer royal, and determined upon founding an observatory. The site—selected by Wren—was a commanding eminence in Greenwich Park, in former times the seat of Duke Humphrey’s tower, within view of all vessels passing along the Thames; a spot which Piazzi was accustomed to call the “paradise” for an observer; being free from a fluctuating atmospheric refraction which annoyed him in the climate of Sicily. The foundation-stone was laid August 10th, 1675. An original inscription, still existing, states the design of the building—the benefit of astronomy and navigation. The observatory has been successively under the superintendence of Flamstead, Halley, Bradley, Bliss, Maskelyne, Pond, and Airy, its present head, with assistants for its proper management. It is not a spot devoted to star-gazing, and the general observance of celestial phenomena, but essentially a place of business, carrying on by day and by night, when the weather permits, those observations of the sun, moon, planets, and principal stars, passing the meridian, from which the nautical almanac derives its information. This has been done with admirable regularity for a long series of years, nor has Europe any data comparable with the Greenwich tables. During the interval in which the office of astronomer royal is necessarily vacant, the business of the observatory proceeds; and that interval is now less than formerly. Thirty-three days elapsed between Bradley’s last observation and Bliss’s first; fifty-three between Bliss’s last and Maskelyne’s first; four between Maskelyne’s last and Pond’s first; and two between Pond’s last and Airy’s first. It has been asserted by Baron Zach, that, if the other observatories had never existed, our astronomical tables would be equally perfect; and Delambre, when delivering an éloge on Maskelyne before the Institute of France, remarked, that if by some grand revolution in the moral or physical world, the whole of the monuments of existing science should be swept away, leaving only the Greenwich observations and some methods of computation, it would be possible to reconstruct from these materials the entire edifice of modern astronomy.

A few years ago it was resolved by the Lords of the Admiralty, that the time should be shown at Greenwich once in every day of the year. This is done by means of a large black ball which surmounts the north-western turret of the observatory. The ball, seen in the vignette, is elevated by machinery to the index, showing the four cardinal points; and, the instant it begins to descend, marks the mean solar time to be 1 P.M. Being plainly observable from the Thames, the arrangement affords a convenient opportunity for seamen to regulate their chronometers and clocks.