138 Prof. Lloyd's Notice of a Magnetic Disturbance 



observations taken at the regular hours immediately prece- 

 ding (2 and 4 a.m. Gotfingen mean time) gave no warning of 

 the approaching change. 



From 6 a.m., for nearly an hour, both magnets returned 

 rapidly, and almost uninterruptedly, towards their mean posi- 

 tions, the declination diminishing, and the horizontal intensity 

 increasing. The latter element reached its maximum at 6 h 

 56 m ; the declination continued to decrease until 7 h 12 m . After 

 this, no very marked change occurred for some time, and the 

 extra observations were discontinued at 8 h 36 m . 



At 10 a.m. the declinometer indicated an increase of de- 

 clination amounting to 18*6 minutes; and the extra observa- 

 tions were resumed, and continued for an hour. By this time 

 (11 a.m.) both instruments had attained nearly their mean 

 positions, from which the observations taken at the regular 

 magnetic hours next following (noon, 2 p.m. 4 p.m.) showed 

 no variation. 



The extra observations were resumed at 5 h 36 m p.m., the 

 bifilar magnetometer then indicating an increase of the hori- 

 zontal intensity, amounting to "0062 of the whole. The ob- 

 servations were continued for more than an hour, but with- 

 out the occurrence of any very marked change. 



The regular observation at 10 p.m. showed a considerable 

 decrease of declination, accompanied by a decrease of hori- 

 zontal intensity ; and at 1 1 p.m. the extra observations were 

 resumed, and continued, with both instruments simultaneously, 

 until Sunday morning. In this interval another very remark- 

 able change took place. The declination, after some irre- 

 gular oscillations, began to increase rapidly, and reached its 

 maximum at ll h 48 m , the deviation from its mean value being 

 then 28*1 minutes. It then returned with a very rapid move- 

 ment, and in eight minutes the magnet traversed 83 divisions 

 of the scale, or 1° of arc; after which it made some smaller 

 oscillations of the same rapid kind. The change of the hori- 

 zontal intensity which occurred at the same time was still more 

 remarkable. This element increased from 1 l h 8 m to 1 1 1 * 20 m ; 

 it then rapidly diminished for 12 minutes more; in another 

 6 minutes it reached a second maximum (at ll h 38 m ); and 

 finally the magnet was driven impetuously beyond the limits 

 of the scale in the opposite direction, the intensity reaching its 

 minimum at ll h 50 m , and the disturbance exceeding the j^th 

 of the whole intensity. The returning oscillation occupied 

 12 minutes more; and at 12 h 2 m the magnet returned to its 

 extreme position on the opposite side, the fluctuation in this 

 time exceeding 111 divisions of the scale. The disturbance 

 during these two hours was characterized by the absence of all 



