Force of the Earth's Magnetism, 29 



time at TeneriffeV 302,2 * 245 ' = 31 I'M ; and at Cu- 



/302 8 .2x245 f QOQ//Q 



mana A / a 3£o\3. 



V 229* 



We have thus, — 



At London 300 



Paris 302.2 



Teneriffe, 1799 . . . .31 



111.11 



Teneriffe, 1822 . . . . 309.1 J 



Cumana, 1799 .... 323.3) 

 Trinidad, 1822 . . . 321.5 J 



The intensity at Christiana and London was compared by 

 means of two of the same needles that were used between Paris 

 and London, Nos. iv. and viii. They were vibrated at Chris- 

 tiana by Mr. Hansteen, in January, 1828 ; in London, by 

 myself, in March ; in Christiana, a second time, in May ; and 

 in London, a second time, in June. Their times of vibration, 

 reduced to a mean temperature (49°), were as follows : — 



Needle iv. Needle viii. 



Christiana, Jan. 10 . Noon . 1097". 25 Noon . 886". 86 



London, March 23 . 1p.m. . 1049". 26 Noon . 850'. 96 



^, . .. ,, _ . Mean a.m.) , nnnl , ,, Mean a.m.) „ m 



Christiana, May 1-4 . > 1099". 11 . > 890". 67 



and p.M.j and p.m. J 



London, June3 . . 1p.m. . 1053". 80 2 p.m. . 853".7 



Whence, by interpolation, we obtain the time of vibration 

 in Christiana, in March, corresponding to the observations in 

 London at that period ; and in London, in May, corresponding 

 to the observations in May, at Christiana. 



N dl 4 I Marcn23 • Christiana . 1098". 45 London . 1049". 26 



\May2 . . Christiana . 1099".ll London . 1051". 76 



N dl 8 | March23 • Christiana . 889". 3 London . 850". 96 



\May 2 . . Christiana . 890". 67 London . 852". 46 



And if we take the horizontal intensity in London as unity, 

 in Christiana it will be as follows : — 



-r, ,, f Comparison in March 



By needle 4-^ ~ r . . _, 

 ' [ Comparison in May 



_, .. n ( Comparison in Mar< 



By needle 8^ r . ,, 



J (Comparison m May 



. 0.9124 



. 0.9157 



Comparison in March . . 0.9157 



. 0.9160 



Mean . . . 0.9147 



