1. Chronograph Room. 2. Old Altazimuth Dome. 3. Safe Room. 4. Computing Room. 5. Bradley's Transit Room. 6. Transit Circle Room. 7. Assistants' Room. 8. Chief Assistant's Room. 9. Computers' Room. 10. Record Rooms. 11. Chronometer Rooms and South-east Dome. 12. Greenhouse and Outbuildings. 14. New Library. 15. Magnetic Observatory. 16. Offices. 19. Sheds. 23. Winch Room for Time-ball. 24. Porter's Lodge. 25. New Transit Pavilion. 26. New Altazimuth Pavilion. 27. Museum: New Building. 28. South Wing " 29. North Wing " 30. West Wing " 31. East Wing " F. Rooms built for Flamsteed. H. Added by Halley. B. " Bradley. M. " Maskelyne. A. " Airy. F'F'. Flamsteed's boundaries. M'M'. Maskelyne's " 1790. P'P'. Pond's " 1814. A'A'. Airy's " 1837. A"A". Airy's " 1868. Beyond the Magnetic Observatory the ground widens out into an area about equal to that of the northern part, and the new building just completed, and which is now emphatically 'The Observatory,' stands clear before us. The transfer to this stately building of the computing rooms, libraries, and store rooms has been aptly described as a shift in the latitude of Greenwich Observatory, which still preserves its longitude. It may be noted that the only two buildings of any architectural pretensions in the whole range are--Flamsteed's original observatory, built by Sir Christopher Wren, and containing little beyond the octagon room, in the extreme north; and this newest building in the extreme south. This 'New Observatory,' like the old, and like the great South-eastern tower, is an octagon in its central portion. But whilst the two other great buildings are simply octagonal, here the octagon serves only as the centre from which radiate four great wings to the four points of the compass. The building is by far the largest on the ground, but in little accord with the popular idea of an astronomer as perpetually looking through a telescope, carries but a single dome; its best rooms being set apart as 'computing rooms,' for the use of those members of the staff who are employed in the calculations and other clerical work, which form, after all, much the greater portion of the Observatory routine. An observer with the transit instrument, for instance, will take only three or four minutes to make a complete determination of the place of a single star. But that observation will furnish work to the computers for many hours afterwards. Or, to take a photograph of the sun will occupy about five minutes in setting the instrument, whilst the actual exposure will take but the one-thousandth part of a second. But the plate, once exposed, will have to be developed, fixed, and washed; then measured, and the measures reduced, and, _on the average_, will provide one person with work for four days before the final results have been printed and published.