Masterpieces of Science 



the magnet is most extensive; while when the 

 sun's face is clear of spots, the needle vibrates 

 over its smallest diurnal arc. 



Then the intensity of the magnetic action has 

 been found to depend upon solar influences. 

 The vibrations by which the needle indicates 

 the progress of those strange disturbances of the 

 terrestrial magnetism which are known as 

 magnetic storms, have been found not merely to 

 be most frequent when the sun's face is most 

 spotted, but to occur simultaneously with the 

 appearance of signs of disturbance in the solar 

 atmosphere. For instance, during the autumn 

 of 1859, the eminent solar observer, Carrington, 

 noticed the apparition of a bright spot upon the 

 sun's surface The light of this spot was so 

 intense that he imagined the screen which shaded 

 the plate employed to receive the solar image 

 had been broken. By a fortunate coincidence 

 another observer, Mr. Hodgson, happened to be 

 watching the sun at the same instant and wit- 

 nessed the same remarkable appearance. Now 

 it was fcund that the self-registering magnetic 

 instruments of the Kew Observatory had been 

 sharply disturbed at the instant when the bright 

 spot was seen. And afterward it was learned 

 that the phenomena which indicate the pro- 

 gress of a magnetic storm had been observed in 

 many places. Telegraphic communication was 

 interrupted, and at a station in Norway the 

 telegraphic apparatus was set on fire; auroras 

 appeared both in the northern and southern 

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