22 Captain Sabine's Experiments on the 



in each of the other fifteen months, and continue an increase 

 of0".5 in each of the remaining months of 1823, we shall 

 make the best arrangement, perhaps, that circumstances will 

 permit, for the rate of this needle in London corresponding to 

 the observations made with it elsewhere. 

 With needle No. 6 we have, in 



1821, August, Regent's Park. Th. 60°, Arcs 20° to 2°. Rate 62i".12 



+ .0 + 0".98 = 622".l. 

 1821, October, Regent's Park. Th. 55°, Arcs 30° to 10°. Rate 619".5 



+ 0".63 + 4".02 - 624".0. 

 1823, April, Chiswick. Th. 42°, Arcs 30° to 5°. Rate 634".2 + 1".82 



+ 2".75 = 638".8. 



1828, September, Chiswick. Observed by Mr. David Douglas. Th. 67°, 



Arcs 30° to 5°. Rate 636".9— 0".76 + 2".76 = 638".9. 



1829, July, Chiswick. Th. 65°.5, Arcs 30° to 5°. Rate 637".0 — 0".56 



+ 2".76 = 63 9". 2. 



1821, August, Regent's Park . . . 622".l 



1821, October, Regent's Park . . . 624"»0 



1823, April, Chiswick ...» 638".8 



1828, September, Chiswick . . . 638".9 



1829, July, Chiswick . . . 639".2 



Hence we perceive that this needle also lost a portion of its 

 magnetism between 1821 and 1823; but that it has been sta- 

 tionary from April 1823, to the present time. If, then, we 

 distribute the total increase in the time of vibration between 

 October 1821 and April 1823, 14".8 in eighteen months, in 

 the following manner, viz. — An increase of 1".5 in each of the 

 first five months ; of 1" in each of the next five months ; and 

 of 0".5 in each of the remaining eight months; we may consider 

 the time of vibration in London during those months as satis- 

 factorily represented by the interpolated rates. 



On a review of the degree of permanency with which the 

 needles have preserved their magnetism, we perceive that three 

 of them have undergone no alteration in that respect in the 

 six years intervening between 1823 and 1829, during which 

 time they have been kept in pairs, and the small boxes, each 

 containing a pair, tied up together. This mode of keeping 

 needles has the advantage of rendering them less liable to be 

 injured by the accidental approach of iron or of a magnet, 

 than if they were kept separately. Their being kept in pairs, 

 also, probably contributes to preserve their magnetism unim- 



