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.
PLAN OF OBSERVATORY AT PRESENT TIME.
(For key to plan, see p. 135.)
Key to the Plan of the Observatory on Page 134.
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.