344 



Report of the Kew Committee. 



for their instruments, and suggests that the scale- values should be as 

 follows : — 



For the Declination 1 mm. 3D = 1'. 



Bifilar 1 mm. £11 = 0*0005 mm. mgr. units. 

 „ Balance 1 mm. 5V= 0*0005 ,, " „ 



The following are the values of the ordinates of the various photo- 

 graphic curves as determined at the various dates stated : — 



Declination 1 inch=0° 22'*04. 1 mm.=0° 0'-'87. 

 Bifilar Jan. 3, 1882, for 1 inch £H=0*0450 foot grain units. 



„ 1 mm. „ =0'0008 mm. mgr. units. 

 „ Mar. 27, „ „ 1 inch „ =0-0222 foot grain units.. 



,, 1 mm. ,, =0*0004 mm. mgr. units. 

 Balance Jan. 6, ,, 1 inch e)V=0*0341 foot grain units. 



,, 1 mm. „ =0*0006 mm. mgr. units. 

 The Committee having been asked bj the Secretaries of the Inter- 

 national Polar Commission to furnish that body with copies of their 

 hourly determinations of the magnetic elements, recommenced the 

 tabulation of the curves which had been suspended in 1879. (See 

 Report for 1880, p. 4.) 



With a view, however, of reducing the labour of tabulation, it was 

 decided that a sufficient degree of accuracy and greater rapidity would 

 be obtained by reading the curves by the unassisted eye, without the 

 aid of the tabulating frame and vernier hitherto employed. Scales 

 graduated on glass plates have therefore been prepared, and the 

 curves tabulated from August 1st up to the present date by this 

 means ; the declination being recorded to a tenth of a minute of arc, 

 and the force-traces to the tenth of a millimetre. 



In order to obtain a record of the more rapid changes which take 

 place during magnetic storms, a trial has been in progress since July 4 

 of the highly sensitive argentic gelatino-bromide photographic paper 

 prepared by Messrs. Morgan and Kidd. 



The results of the experiment show that the paper indicates clearly 

 small movements of the magnet which the waxed paper is unable to 

 register, and also that less gas-light is needed for the purpose of illu- 

 mination. . 



Three magnetic storms, or periods of considerable disturbance of the 

 needles, have been registered during the year; viz., on April 17th and 

 20th and on October 2nd. All were accompanied by auroral displays, 

 but these were only observed in this country on the last date. 



The Committee have to acknowledge with thanks the receipt of 

 photographic copies of traces during those magnetic disturbances 

 from the Observatories at the Mauritius, Melbourne, Toronto, and 

 Batavia. 



