

83 



In the Arctic Expeditions of 1818, 1819, and 1820, I had an op- 

 portunity of measuring the intensity of the magnetic force at several 

 stations in the immediate vicinity of the dip of 90 ; and in the years 

 1821 and 1822, of comparing these measures with others made at 

 several points of the coasts of Europe, Africa, and America, and at 

 islands in the Atlantic Ocean (which I visited for the purpose of 

 making observations with the pendulum), in dips which, including the 

 Arctic stations, varied from to 88 47'. The result of this compa- 

 rison was to place beyond a question the irreconcilability of the phe- 

 nomena with the supposition of a coincidence between the points of 

 90 of dip and of the maximum of force. For example, the mag- 

 netic force was found to be considerably greater at New York, where 

 the dip was not more than 73, than at the stations in the Polar Sea 

 where it was nearly 90 ; and by graphical delineations, according to 

 well-known methods, in which all the observations were taken into 

 the account, it was shown that whilst the dip of 90 could not be in 

 a more southerly latitude than 70, the greatest intensity of the 

 force would be found somewhere about the 53rd parallel in the 

 vicinity of Hudson's Bay, not less than 1000 geographical miles 

 distant from the point of 90 of dip with which it had been supposed 

 to coincide, 



The hypothesis, so generally put forward in the elementary trea- 

 tises on Magnetism of that period, was therefore shown to be no 

 longer tenable. It was in fact specially one of that class of specula- 

 tions designated by Bacon as "anticipations of nature," of which 

 it is so commonly the fate to be swept away, as knowledge advances 

 by that more slow and gradual, but more philosophical and certain 

 "interpretation of nature," which results from a strictly inductive 

 process. 



Steadily pursuing this last-named process, the Royal Society after 

 provision had been made by the establishment of Colonial Magnetic 

 Observatories for a systematic examination of the phenomena of the 

 variations of comparatively small amount, which are produced at the 

 surface of our planet by the influence of other bodies of our system; 

 and by the Antarctic Expedition of Sir James Ross, for the magnetic 

 survey of such portions of the higher latitudes of the southern hemi- 

 sphere as are accessible to navigation, recommended to Her Majesty's 

 Government, that in the northern hemisphere a magnetic survey 



G2 



