30 Captain Sabine's Experiments on the 



The dip in the spring of 1828, at Christiana, was observed 

 by M. Hansteen to be 72° 16'.2 ; in London, at the same pe- 

 riod, it was 69° 47': whence the total magnetic intensity at 



n . ... . 0.9147 x Cos. 69° 47' , n ™ .-* .' . 



Christiana, is as = l.Oo/o, to unity in 



Cos. 72° 16'.2 ' ' 



London ; and the needle which makes the time of vibration 

 300" in London, would require 294".47 in Christiana. 



The two stations common to M. Hansteen's observations and 

 mine, are Drontheim and Hammerfest. At Drontheim, in 1825, 

 M. Hansteen found that his horizontal needle, which at Chris- 

 tiana made 300 vibrations in 816", required 866 // .77 for the 

 same number ; he also observed the dip in that year at 

 Christiana 72° 26'; and in Drontheim, 74° 42'. The num- 

 bers 816", and 866". 77, reduced to the direction of the 

 dipping-needle, became 448". 30, and 445".30 ; and the rate 

 of vibration at Drontheim corresponding to 300" in London, 



is 3 Q0 '^^f/ 3 ° = 292".5. In 1827, Professor Keilhau made 

 448 2 .30 



a second comparison between Drontheim and Christiana, with 



a horizontal needle which had been compared at Christiana with 



M. Hansteen's. M. Keilhau made the relative times 816", and 



869".7, which reduced to the direction of the dipping-needle, 



are 448".30 and 446".8 ; and the rate of vibration at Drontheim, 



relatively to 300" in London, is 293.5. We have thus— 



Sabine, in 1823 . . . 294'M 



Hansteen, in 1825 . . . 292". 5 



Keilhau, in 1827 . . . 293". 5 



At Hammerfest, in 1827, Professor Keilhau observed 937".4 

 corresponding to 816" at Christiana. These make the relative 

 times in the magnetic direction, (the dip at Hammerfest being 

 77° 13', page 27) 448".30 and 440".94 ; and the rate of vibra- 

 tion at Hammerfest, corresponding to 294".47 in Christiana 

 or 300" in London, 289".6. A previous observation at Ham- 

 merfest is recorded by M. Hansteen (Astr. Nach. No. 146) to 

 have been made, in 1825, by some gentlemen who had under- 

 taken the charge of one of M. Hansteen's needles in a voyage 

 from Norway to Archangel, and who found the time of hori- 

 zontal vibration 930".8, relatively to 816" at Christiana. This 



