4 8 



same solar mendian to the centre of the sun's disc. In 

 1913, which, as noted above, was a year in which the sun's 

 surface was almost completely free from spots, there were 

 no days of great magnetic disturbance, and only one was 

 classified as of small disturbance. 



The Magnetical Department has had a close bearing 

 upon the science of navigation. Thus, when steamships 

 were substituted for sailing vessels, and ships built of iron 

 for those of wood, it fell to Airy to investigate several import- 

 ant problems arising from the effect of these changes on the 

 magnetic compass, and in quite recent years the introduction 

 into ships of powerful dynamos for the generation of electricity 

 has rendered it necessary to investigate the effect of these 

 on the behaviour of chronometers carried in the same vessels. 

 This inquiry was carried out at Greenwich in the years 1911- 

 1912. Lastly, just as Halley, the second Astronomer Royal, 

 prepared the first magnetic chart of the world, so at the present 

 time it is at the Royal Observatory that the latest magnetic 

 chart of the world is in course of preparation. 



The Report of 1914 makes reference to the completion 

 of the new Magnetograph House. This has been set up a. v . a 

 considerable distance from the main Observatory buildings, 

 in the same enclosure as the Magnetic Pavilion erected 

 by Christie. The Magnetograph House consists of a small 

 room inside a larger one, the inner room being fitted with 

 an automatic arrangement for securing a uniform temperature 

 throughout the year. As the photographic sheets of the 

 self-recording instruments have to be changed every day, 

 provision is made by means of shutters in the walls of the 

 inner room that this can be done without the observer 

 actually entering it. The new instruments installed in the 

 room, and the recording apparatus, were constructed by the 

 CAMBRIDGE SCIENTIFIC INSTRUMENT COMPANY. 



The Meteorological Department is closely connected with 

 the Magnetical, and it is only necessary to say here that no 

 other meteorological observatory in the British Isles of the 

 same full equipment possesses so long and continuous a 

 record. 



Two other departments of Greenwich Observatory, the 

 fundamental importance of which will be recognised by every 

 one, call for mention. These are the departments of Chrono- 

 meters and of Clocks and Time Service. All the chronometers 

 for the Royal Navy are tested and rated at Greenwich, and are 

 returned thither for re-examination at the end of every 

 time of service abroad. The Clock Department is concerned 



