THE NATIONAL PHYSICAL LABORATORY. 



Report on the Observatory Department for the Year 

 ending December 31, 1900. 



The work at the Kew Observatory in the Old Deer Park at Richmond, 

 now forming the Observatory Department of the National Physical 

 Laboratory, has been continued during the year 1900 as in the past. 



This work may be considered under the following heads : — 



I. Magnetic observations. 

 II, Meteorological observations. 



III. Seismological observations. 



IV. Experiments and Researches in connexion with any of the 



departments. 

 V. Verification of instruments. 

 VI. Rating of Watches and Chronometers. 

 VII. Miscellaneous. 



I. Magnetic Observations. 



The Magnetographs have been in constant operation throughout 

 the year, and the usual determinations of the Scale Values were made 

 in January. 



The ordinates of the various photographic curves representing 

 Declination, Horizontal Force, and Vertical Force were then found 

 to be as follows : — 



Declinometer : 1 cm. = 0° 8 ,- 7. 

 Bifilar, January, 1900, for 1 cm. SH = 0-00051 C.G.S. unit. 

 Balance, January, 1900, for 1 cm. SV = 0-00049 C.G.S. unit. 



The distance between the dots of light upon the vertical force 

 cylinder having become too small for satisfactory registration, the dots 

 were separated on June 20 by slightly altering the position of the 

 zero mirror. 



The curves have been quite free from any large fluctuations ; indeed, 

 no unusual disturbance has been registered for some time past. The 

 principal variations that were recorded during the year took place on 

 the following days : — 



• January 19th-20th ; March 8th-9th and 13th ; May 5th. 



The hourly means and diurnal inequalities of the magnetic elements 

 for 1900, for the quiet days selected by the Astronomer Royal, will be 

 found in Appendix L 



