506 The Astronomer Royal on a recent Magnetic Disturbance. 



the declination needle increase as the north end of the needle 

 moves towards the east, and that the reading for the astro- 

 nomical meridian is 269° 51' 45" nearly; that the increasing 

 readings of the vertical-force magnetometer imply increasing 

 vertical force, one division being equal to 0*000471 of the 

 whole vertical force ; and that the increasing readings of the 

 horizontal-force magnetometer imply increasing horizontal 

 force, one division being equal to 0*0022 14 of the whole ho- 

 rizontal force. 



Early in the morning of Sept. 25, the needles were in an agi- 

 tated state. During the appearance of an aurora, additional 

 observations were taken; and the declination needle in less 

 than three hours traversed an arc of 34'. After this the needles 

 were in a tolerably quiet state, and extraordinary observations 

 were discontinued. 



The observation at 10 h a.m. showing a change of 17' of 

 arc from the previous reading, at 8 h a.m., extra observations 

 were again resumed,, and continued till ll h a.m.; nothing re- 

 markable appearing during this time, they were again discon- 

 tinued. 



At 2 h p.m., Gbttingen mean time, it was evident that all 

 the needles were affected by some unusual cause of disturbance, 

 and incessant observations were at once commenced, the in- 

 struments being observed successively, as quickly as one ob- 

 server could take them. At 3 h 53 m Mr. Hind joined, and 

 subsequently Messrs. Dunkin and Paul. From this time to the 

 discontinuance of the observations two persons were constantly 

 engaged, one taking the observations with the vertical-force 

 magnetometer, the other, those of the declination needle and 

 of the horizontal-force magnetometer. About 2 11 40 m p.m., 

 the motions of the needles became very peculiar ; the vibra- 

 tions of the declination needle and of the vertical-force mag- 

 netometer being quite destroyed ; and those of the horizontal- 

 force magnetometer being reduced to a continuous succession 

 of jerks or starts. It will perhaps contribute to clearness if 

 the motions of the three instruments are now separately de- 

 scribed. 



Declination Needle. — Every change in this instrument from 

 one position to another was by sudden impulses ; after each of 

 these it was stationary, for intervals varying from 5 s to 20 s ; 

 then it was forced again to another position, and was again 

 stationary without the slightest motion; and so on success- 

 ively. 



At 3 h 30 ra the changes from one position to another became 

 very decided, but the motions still partook of the same cha- 

 racter ; absolute rest and jerking motion followed alternately : 



