[ 310 ] 

 XL. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 246.] 



November 15, 1860. — Major-General Sabine, R.A., Treasurer and 



Vice-President, in the Cbair. 

 T^IIE following communication was read : — 



-*- " On the Laws of the Phenomena of the larger Disturbances 

 of the Magnetic Declination in the Kew Observatory : with notices 

 of the progress of our knowledge regarding the Magnetic Storms." 

 By Major-General Edward Sabine, R.A., Treas. and V.P. 



The laws manifested by the mean effects of the larger magnetic 

 disturbances (regarded commonly as effects of magnetic storms) 

 have been investigated at several stations on the globe, being chiefly 

 those of the British Colonial Observatories ; but hitherto there" has 

 been no similar examination of the phenomena in the British Islands 

 themselves. The object of the present paper is to supply this de- 

 ficiency, as far as one element, namely the declination, is concerned, 

 by a first approximation derived from the photographs in the years 

 1858 and 1859, of the self-recording declinometer of the observatory 

 of the British Association at Kew ; leaving it to the photographs 

 of subsequent years to confirm, rectify, or render more precise the 

 results now obtained by a first approximation. The method of in- 

 vestigation is simple, and may be briefly described as follows : — 



The photographs furnish a continuous record of the variations 

 which take place in the direction of the declination-magnet, and ad- 

 mit of exact measurement in the two relations of time, and of the 

 amount of departure from a zero line. From this automatic record, 

 the direction of the magnet is measured at twenty-four equal inter- 

 vals of time in every solar day, which thus become the equivalents 

 of the "hourly observations" of the magnetometers in use at the 

 Colonial Observatories. These measures, or hourly directions of the 

 magnet, are entered in monthly tables, having the days of the month 

 in successive horizontal lines, and the hours of the day in vertical 

 columns. The "means" of the entries in each vertical column indi- 

 cate the mean direction of the magnet at the different hours of the 

 month to which the table belongs, and have received the name of 

 " First Normals." On inspecting any such monthly table, it is at 

 once seen that a considerable portion of the entries in the several 

 columns differ considerably from their respective means or first nor- 

 mals, and must be regarded as " disturbed observations." The laws 

 of their relative frequency, and amount of disturbance, in different 

 years, months and hours, are then sought out, by separating for that 

 purpose a sufficient body of the most disturbed observations, com- 

 puting the amount of departure in each case from the normal of the 

 same month and hour, and arranging the amounts in annual, monthly, 

 and hourly tables. In making these computations, the first normals 

 require to be themselves corrected, by the omission in each vertical 

 column of the entries noted as disturbed, and by taking fresh means, 

 representing the normals of each month and hour after this omission, 

 and therefore uninfluenced by the larger disturbances. These new 



