Oh the Nmtk-tuest Magnetic Pole. S;l 



the embarrassment of southern magnetic poles, beyohd the re- 

 C]uisite one of the south end of the earth's axis: and all future 

 reasoning (till experience and experiment carry us further) must 

 be founded less on hypothesis, and more on fact, than has hither- 

 to been the case. 



Having premised thus much, we come to the consideration of 

 the wonderful and inexplicable phaenomenon in nature, the ac- 

 countmg for which has induced so many eminent scientific cha- 

 racters to form the theories briefly mentioned above.— Professor 

 Gillebrand having compared his own observations of the varia- 

 tion with those of others, ascertained that it gradually increased 

 westward. In the year 1576 the variation was found to be 1 1" 15' 

 east, in London. It diminished gradually till 1662 (or 165/ by 

 other accounts), when it became nothing; or in other words 

 the magnetic needle pointed to the true north. In 1666 Mr 

 Sellers made the variation 0" 'M' west. Since that period the 

 variation has been increasing westward, and during the three 

 last years it has remained nearly stationary. In comparing its 

 progress during similar periods, "it does not appear that the rate 

 of increase is equable, as it varies from one or two minutes to 

 a medium annual increase of 9' 48".— In the Royal Society-s 

 Rooms, the mean variation in June 1817 was 24° 17' 54"; and 

 in June 1818 it was in mean quantity 24° 17'. In June 1819 

 it was found to be 24» 15' 43"; from which it would seem that 

 It had begun to return. It was found, by Captain Cook, that 

 the same observers, with the same compass, in the same day 

 made a difference of five and six degrees ; and nearly the doub'e 

 of this was found as a dif!"erence between the variation taken on 

 the ice, and on board ship in Baffin'^ Ray. This leads to the 

 clear conclusion, that observation on terra firma can alone be 

 depended upon for real acairucy. 



The dip of the needle, or its inclination to the nearest pole 

 (and I have some reason to conclude that this also is subject to 

 a daily small variation), was an accidental discovery, made bv 

 Mr. Norman, in balancing his needles. It was in'l576 found 

 to be 71" 50' at London; and in June 1819 it was about 70^51' 

 in the Royal Society's Rooms. In the very same situation, at 

 ddFereiit periods, both the variation and dip are different; and 

 the di'j does not correspond to change in latitude unrlcr the same 

 meridian; nor is the same dip given by the same dipping needle, 

 at sea, on the same day. This again indicates the necessity of 

 observing the dip also on shore, when real accuracy is wanted. 

 If the variation and dip were not constantly altering' in the same 

 place, a certain theory might be arrived at ; but when the con- 

 trary proves to be the fact, the attempts made to lav down on the 

 globe a curve of no magnetic variation, is useless, i'f not absurd 



Vol.57. No. 274. /-V/-. Ib21. M .\ 8„,aii 



