ON MAGNETIC OBSERVATIONS. 



149 



Report of the Committee, consisting of Professor W. Grylls Adams 

 {Chairman and Secretary), Sir William Thomson, Professor 

 Gr. H. Darwin, Professor Gr. Chrystal, Professor A. Schuster, 

 Professor KiJCKER, Mr. C. H. Carpmael, Commander Creak, the 

 Astronomer Eotal, Mr. William Ellis, and Mr. Gr. M. W^hipple, 

 appointed for the purpose of considering the best means of 

 Comparing and Reducing Magnetic Observations. 



In accordance witli the arrangements made last year for determining the 

 mean diurnal range from the observations taken on five days in each 

 month, the following list of quiet days during the year 1890 has been 

 selected by the Astronomer Royal as suitable for the determination of the 

 magnetic diurnal variations : — 



Quiet Days in 1890. 



During the past year the magnetic survey of the United Kingdom, 

 now in progress under the supei'intendence of Professors Riicker and 

 Thorpe, has advanced rapidly. Messrs. Gray, A.R.C.Sc, and Watson, 

 B.Sc, A.R.C.Sc, are at present working in Ireland and Scotland respec- 

 tively. A body of computers has been organised at South Kensington, 

 so that the reductions are pi'oceeding j^ari passu, with the observations, 

 and by the end of this summer complete observations will have been made 

 at more than 600 stations in the British Isles. 



On June 18 last, in a paper read before the Royal Society on the 

 * Comparison of SimuUaneons Magnetic Disturbances at several Observa- 

 tories, and Determination of the Value of the Gaussian Coefficients for 

 those Observatories,' the Chairman pointed out the importance of adopt- 

 ing the same scale- values for similar instruments at different observatories, 

 «specially at new observatories which have been recently established, and 

 discussed special magnetic disturbances, especially the disturbances of a 

 great magnetic storm which occurred on June 24 and 25, 1885, for which 

 photographic records have been obtained from seventeen different obser- 

 vatories : eleven in Europe, one in Canada, one in India, one in China, 

 one in Java, one at Mauritius, and one at Melbourne. 



In this paper the records are discussed and compared, tables are 

 formed of the simultaneous disturbances, and the traces are reduced to 

 Greenwich mean time and brought together on the same plates arranged 

 on the same time-scale. Plates I. and II. show the remarkable agreement 

 between the disturbances at the different observatories, and the tables 

 show that the amount of disturbance, especially of horizontal magnetic 

 force, is nearly the same at widely distant stations. 



