The Astronomer Royal on a recent Magnetic Disturbance. 509 



At 3 h 35 m 21 s , the marked end of the needle (which is to- 

 wards the east, the needle being transverse to the magnetic 

 meridian) was resting on the eastern Y, or apparatus intended 

 for guarding the needle, dipping as much as the frame per- 

 mitted it, and held there apparently by a great power ; in 

 this situation it remained for ten minutes, till 3 h 45 m . 



h m s d 



At 3 45 42 pm., Gottingen mean time, scale read 73' 1 

 46 23 ... ... 689 



50 31 ... ... 63-4 



57 38 ... ... 57-7 



58 58 ... ... 55-6 



4 13 36 ... ... 629 



669 

 556 

 606 

 532 

 68-3 

 53-8 

 503 

 45-6 

 409 

 33-7 

 1 3 25 ... ... 361 



About 6 h 19 m p.m., the needle assumed a steadier appear- 

 ance, having a motion something like vibration, but exceed- 

 ingly irregular. 



Horizontal -Force Magnetometer. — The horizontal-force 

 magnetometer was not less affected than the other two instru- 

 ments. The effect on its vibrations was however peculiar to 

 itself: in the midst of its swings it was suddenly checked, and 

 held in that place for a second or two, then hurried back- 

 wards, again suddenly stopped, and then forced back in the 

 contrary direction ; these checks were sometimes at 5 s , some- 

 times at 1 s , after arriving at its limit. They were most stri- 

 king. From experience with this instrument We are accustomed 

 to look for an almost imperceptible motion at the extremities 

 of the vibrations, then to see it move slowly in the opposite 

 direction, quickly in the centre of swing, slowly towards the 

 end, then return, and so on ; but to see it, almost in the same 

 instant, moving rapidly and absolutely motionless, was very 

 striking and strange to the observers. 



This instrument was less affected in the early part of the 

 day than either of the others. About noon it showed signs 

 of being under the influence of some disturbing cause : the 

 scale then read 55 d, 8 ; at l h 50 m the reading increased to 

 58 d -6 ; at 2 h m to 59 d, 3 ; at 2 h 10 m to 60 d, l ; it then oscillated 



