On Magnetic Observations transmitted from York Fort. 145 



where it was nearly 90° ; and by grapliieal deliueatlons, 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 tban 70°, the greatest intensity of the 

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

 vicinity of Hudson's Baj', 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 toller Majesty's 

 Government, that in the northern hemisphere a magnetic survey 

 should be made of those parts of the British possessions which were 

 adjacent to the position which observation had indicated as that of the 

 principal maximum of the magnetic force in that hemisphere. This 

 recommendation was carried out in 1843 and 1844, and the particulars 

 of the survey, together with the conclusions derived from it, form 

 No. VII. of the magnetic contributions ia the ' Philosophical Trans- 

 actions' for 1846, Art. XVII. The geographical position of the maxi- 

 mum of magnetic force derived from the combination of the 7S sta- 

 tions of that survey was 52° 19' N. and 91° 59' W. of Greenwich, and 

 the absolute value of the force at its point of maximum was found to 

 be I4'21 in British units (/. e. of mass, a grain; of time, a second; and 

 of space, a foot). As both the geographical position of the point of 

 maximum and the absolute value of the force prevailing there, are sub- 

 ject to a secular variation, of which the nature, the period, and the 

 epochs are desiderata of the highest theoretical importance, — and as 

 the determinations which are now made may therefore probably be 

 referred to as data by remote posterity, — their confirmation, by the 

 observations of a second observer visiting the same localities within a 

 few years of the same date, furnished with different instruments, and 

 pursuing in some respects different methods, was viewed as a circum- 

 stance much to be desired by the Committee of the Royal Society 

 appointed, at the request of Her Majesty's Government, to suggest 

 scientific desiderata, to be accomplished by IMr. Palliser's North 

 American Expedition, 



York Fort had been one of the stations visited by Lieut, (now 

 Lieut. -Col.) Lefroy, in the Survey of 1843-44. It is situated 



Phil. Mag. S. 4. Vol. 16. No. 105. Aug. 1858. L 



