The 'New Observatory' in the south ground is crowned indeed with the dome devoted to the great Thompson photographic refractor, but this is not its chief purpose. Its principal floor contains four fine rooms which are used as 'computing rooms'--for the office work, that is to say, of the Observatory. Of these the principal is in the north wing, where the main entrance is placed, and is occupied by the Astronomer Royal and the two chief assistants. The basement contains the libraries and the workshops of the mechanics and carpenters. The upper floor will eventually be used for the storage of photographs and manuscripts, and the terrace roofs of the four wings will be exceedingly convenient for occasional observations, as, for example, of meteor showers. The central dome, which rises high above the level of the terraces, is the only room in the building devoted to telescopic work. As in the New Altazimuth building, a ring of circular lights just below the coping of the wall recalls the portholes of a ship, and again reminds us of the connection of the Observatory with navigation. [Illustration: THE WORKSHOP.] Here the spectroscope is now placed, but not, as it happens, on the Thompson refractor. The equatorial mounting in this new dome is a modification of what is usually called the 'German' form of mounting--that is to say, there is but one pier to support the telescope, and the telescope rides on one side of the pier and a counterpoise balances it on the other The 'Great Equatorial,' on the other hand, is an example of the English mounting, and has two piers, one north and the other south, whilst the telescope swings in a frame between them. In the new dome three telescopes are found rigidly connected with each other on one side of the pier, the telescopes being (1) the great Thompson photographic telescope, double the aperture and double the focal length of the standard astrographic telescope used for the International Photographic Survey; (2) the 12-3/4 telescope by Merz, that used to be in the great South-East dome, but which is now rigidly connected with the Thompson refractor as a guide telescope; and (3) a photographic telescope of 9 inches aperture, already described as the 'Thompson' photo-heliograph, and used for photographing the sun or in eclipse expeditions. The counterpoise to this collection of instruments is not a mere mass of lead, but a powerful reflector of 30 inches' aperture, and it is to this telescope that the spectroscope is now attached. At the present time, however (August, 1900), regular work has not been commenced with it. [Illustration: THE 30-INCH REFLECTOR WITH THE NEW SPECTROSCOPE ATTACHED.]