Description of the Kew Observatory. 143 



are compared with one or more standards in a vertical position, 

 readings being taken in the majority of instances at intervals of 10. 

 There are special arrangements for securing and maintaining a 

 uniform temperature. 



SECOND FLOOK. 



New Addition to West Wing. These rooms, built in 1.892, are not 

 jet much used. They contain a Hypsometer (17), of the form in use 

 at the Bureau International at Sevres (see Dr. Guillaume's ' Thermo- 

 metrie de Precision,' p. 113), and an air pump with other apparatus 

 employed in investigating the behaviour of aneroid barometers. 



Superintendent's Room. This contains a considerable part of the 

 Library. 



First Assistant's Room. This room is chiefly devoted to the mag- 

 netic computing work ; it contains an apparatus for testing the shades 

 of sextants (' Boy. Soc. Proc.,' vol. 35, p. 42). 



Optical Room. This is chiefly used for testing and marking 

 binoculars, Navy telescopes and air meters ; it also contains part of 

 the Library. 



The Library. A room similar in size to the Superintendent's 

 room, lined with book-cases. It contains a large glycerine barometer 

 (18) erected by Jordan in 1879, not now in action ('Boy. Soc. Proc./ 

 vol. 30, p. 105). 



THE BOOF. 



The Dome contains the photoheliograph erected in 1856 by Dr. 

 Warren De la Bue. For some years the instrument has been used 

 only for eye observations of sun-spots. Work done with it in earlier 

 years is described in the ' Phil. Trans.,' (vol. 159, pp. 1 110, and 

 vol. 160, pp. 389496). 



The Lens Room. This contains the self-recording apparatus (19), 

 designed by Beckley (' B.A. Beport,' 1858, p. 306, and ' Beport of 

 Met. Com.,' 1867) for the Bobinson anemometer, which is placed 

 above the dome. A long rod is geared to the anemometer spindle 

 by means of an endless screw. At the lower end of this rod is a 

 gearing by which a small horizontal cylinder is made to effect one 

 complete revolution for every 50 miles of wind. The cylinder is 

 encircled by a spiral knife-blade shaped strip of metal, and the 

 edge of this strip touches a chronograph cylinder beneath it, at one 

 point only at a time. During a complete revolution of the small 

 cylinder each point of the spiral strip comes in contact with the 

 chronograph. The chronograph sheet being of metallic register 

 paper, the contacts of the spiral strip are recorded. There is a 

 similar arrangement for recording the wind direction, the small 



