150 REPORT — 1891. 



An attempt has also been made to apply the Gaussian analysis to 

 sudden magnetic disturbances, and, with a view to their application in 

 fature work, the Talues of the Gaussian coeflBcients have been obtained 

 for twenty different observatories, and the numerical equations formed 

 for the elements of magnetic force in three directions mutually at right 

 angles, and also the equation for the magnetic potential in terms of the 

 Gaussian constants to the fourth order. The observatories of Washing- 

 ton and Los Angeles in the United States of America are included in 

 this list. 



During the past year a very interesting volume has been published, 

 giving the magnetic observations at the United States Naval Observa- 

 tory at "Washington for 1888 and 1889. In accordance with the recom- 

 mendatioi^ made at the International Conference held at Washington in 

 1884 the hours adopted in these American tables are for the seventy-fifth 

 meridian (west of Greenwich), mean time. 



The results of the Washington observations are contained in ten 

 tables, as follows : — 



Table I. — Mean hourly values of declination for 1888-89. 

 Table II. — Mean hourly declination for each month of 1888-89, taken from monthly 



composite curves. 

 Table III. — Mean hourly values of horizont.il force for each month of 1889 in c.g.s. 



■units (dynes). 

 Table IV. — Mean hourly values of vertical force for each month of 1889 in c.g..s. 



units (dynes). 

 Tables V., VI., and VII. — Hourly values of declination, horizontal force, and vertical 



force respectively. 

 Table VIII. — Summary of disturbances in declination during 1888-89, determined 



from the composite curve. 

 Tables IX. and X.— Observations for 1888-89 for horizontal force and dip respec- 

 tively. 



In addition to the tables there are fourteen plates as follows : — 



Plate I. — Examples of the daily photographic traces of declination, horizontal 

 and vertical force. 



Plate II.— Mean diurnal variation of the magnetic elements for 1889. 



Plates III., IV., V., VI. — Monthly composite curves of declination for 1888 and 

 1889, each plate for six months. 



Plates VII. to XIV. — Comparisons of disturbed days of declination at Washing- 

 ton, Los Angeles, Toronto (Canada), and Pawlowsk (St. Petersburg). 



The traces are all placed for the same time, and are reduced to the 

 same length of base line. In the horizontal-force trace increase of ordi- 

 nate denotes increase of force, and in the vertical-force trace increase of 

 ordinate denotes decreasing force, and the scale-value adopted for both 

 horizontal and vertical force instruments is very nearly the scale-value 

 recommended in the third report of this committee to the British Asso- 

 ciation (1887), viz., 1 centimetre of ordinate='0005 c.g.s. units. 



The Committee entertain hopes that another of their recommendations, 

 to which attention was first drawn in their third report (1887), and to 

 which attention was again drawn in their fifth and sixth reports, viz., 

 the establishment of a Magnetic Observatory at the Cape of Good Hope, is 

 about to be carried out. At a meeting of the Committee held on June 2, 

 1891, at which the Chairman, Sir William Thomson, Professor Riicker, 

 Commander Creak, Mr. Ellis, and Mr. Whipple were present, and at which 

 Mr. Gill also attended at the request of the Committee, a statement was 

 drawn up with regard to the requirements for a Magnetic Observatory 

 at the Cape of Good Hope, and a rough estimate of cost and maintenance 



