Beyond the Record Rooms the boundary turns sharply south, where stands a large octagonal building surmounted by a dome of oriental appearance, a 'circular versatile roof,' as the Visitors would have called it a hundred years ago. This dome--which has been likened, according to the school of æsthetics in which its critics have been severally trained, to the Taj at Agra, a collapsed balloon, or a mammoth Spanish onion--houses the largest refractor in England, the 'South-east Equatorial' of twenty-eight inches aperture. But, though the largest that England possesses, it would appear but as a pigmy beside some of the great telescopes for which America is famous. Beyond this dome the hollow devoted to the Astronomer Royal's private garden reduces the Observatory ground to a mere 'wasp's waist,' a narrow, inconvenient passage from the old and north observatory to the younger southern one. The first building, as the grounds begin to widen out to the south, contains the New Altazimuth, a transit instrument which can be turned into any meridian. A library of white brick and a low wooden cruciform building--the Magnetic Observatory--follow it closely. This latter building houses the Magnetic Department, a department which, though it lies aside from the original purposes of the Observatory, as defined in the warrant given to Flamsteed, is yet intimately connected with navigation, and was founded by Airy very early in his period of office. This deals with the observation of the changes in the force and direction of the earth's magnetism, an inquiry which the greater delicacy of modern compasses, and, in more recent times, the use of iron instead of wood in the construction of ships, has rendered imperative. Closely associated with the Magnetic Department is the Meteorological. Weather forecasts, so necessary for the safety of shipping round our coasts, are not issued from Greenwich Observatory, any more than the _Nautical Almanac_ is now issued from it. But just as the Observatory furnishes the astronomical data upon which the almanac is based, so also a considerable department is set apart for furnishing observations to be used by the Meteorological Office at Westminster for their daily predictions. So far, the development of the Observatory had been along the central line of assistance to navigation. But the 'Magnetic Department' led on to a new one, which had but a secondary connection with it. It had been discovered that the extent of the daily range of the magnetic needle, and the amount of the disturbances to which it was subjected, were in close connection with the numbers and size of the spots on the sun's surface. This led to the institution of a daily photographic record of the state of the sun's surface, a record of which Greenwich has now the complete monopoly. [Illustration: PLAN OF OBSERVATORY AT PRESENT TIME. (For key to plan, see p. 135.)] KEY TO THE PLAN OF THE OBSERVATORY ON PAGE 134.