At first it was supposed that double stars were double only in appearance; one star comparatively near us 'happened' to lie in almost exactly the same direction as another star much further off. It was, indeed, in the very expectation that this would prove to be the case, that the elder Herschel first took up their study. But he was soon convinced that many of the objects were true double stars--members of the same system of which the smaller revolved round the larger--not merely apparently double, one star appearing by chance to be close to another with which it had no connection--but real double stars. The discovery of these has led to the establishment of a new department of astronomy, again scientific rather than utilitarian. [Illustration: DOUBLE-STAR OBSERVATION WITH THE SOUTH-EAST EQUATORIAL. (_From a photograph by Mr. Edney._)] As mentioned above, it is only recently that Greenwich has taken any appreciable part in this work. Under Airy, the largest equatorial of the time had been furnished with a good micrometer, and observations of one or two double stars been made now and again; but Airy's programme of work was far too rigid, and kept the staff too closely engaged for such observations to be anything but extremely rare. And, indeed, when the micrometers of the equatorials were brought into use, they were far more generally devoted to the satellites of Saturn than to the companions of stars. In the main, double-star astronomy has been in the hands of amateurs, at least in England. But the discovery in recent years of many pairs so close that a telescope of the largest size is required for their successful observation, has put an important section of double stars beyond the reach of most private observers, and therefore the great telescope at Greenwich is now mainly devoted to their study. The Astronomer Royal, therefore, soon after the completion of the great equatorial of 28-inches aperture placed in the south-east dome, added this work to the Observatory programme. The 28-inch equatorial is a remarkable-looking instrument, its mounting being of an entirely different kind to that of the other equatorials in the Observatory, with the solitary exception of the Shuckburgh, which is set up in a little dome over the chronograph room. The Shuckburgh was presented to the Observatory in the year 1811, by Sir G. Shuckburgh. It was first intended to be mounted as an altazimuth, but proved to be unsteady in that position, and was then converted into an equatorial without clockwork, and mounted in its present position. The position is about as hopelessly bad a one as a telescope could well have, completely overshadowed as it is by the trees and buildings close at hand. The dome is a small one, and the arrangements for the shutters and for turning the dome are as bad as they could possibly be. It has practically been useless for the last forty years.