146 Royal Society : — 



nearly due north of the point of maximum deduced from that survey, 

 and less than 300 miles distant from it. The intensity of the force 

 at York Fort in July 1843, derived from the combined observations 

 of the inclination and of the horizontal force observed by Gauss's well- 

 known absolute method, was 14-07 ; and by Mr. Fox's statical appa- 

 ratus, taking Toronto as a base, 14'03. We have now to compare 

 with these Lieut. Blakiston's results in August 1857, viz. 14"024 by 

 the combination of the inclination and the absolute horizontal force, 

 and 14'017 by a recent improvement of Dr. Lloyd's statical method, 

 which renders the result independent of changes which may take place 

 in the magnetic moment of the needle employed in the determination. 

 The first of these two last-named results has been computed by Mr. 

 Welsh, of the Kew Observatory, from the observations received from 

 Lieut. Blakiston, who was too much pressed for time by his ap- 

 proaching departure from York Fort to compute them himself. 

 The second is the mean of five determinations on three different 

 days, which were computed by himself on the spot ; they are severally 

 as follows :— August 20th, noon 14-03 



„ 20th, 3 P.M. .... 14-01 



„ 22nd, 5 P.M 14-024 



„ 24th, noon 14-00 



„ 24th, 3 P.M 14-02 



Mean 14-017 



We have therefore by the mean of the two methods in 1843, 

 14-05, and by the mean of the two methods in 1857, 14-02, dif- 

 fering only about j^-yth from each other. As far, therefore, as 

 agreement at a single statio?i may be regarded as confirming the 

 conclusions of the survey of 1843-44, Lieut. Blakiston's results 

 furnish that confirmation ; and judging from the result at the first 

 station at which the comparison has been made, we may anticipate, 

 from the opportunities which he is likely to have of repeating obser- 

 vations at other stations of the former survey, as well as of adding sta- 

 tions previously unvisited, that the ultimate conclusion in respect to 

 the absolute value of the magnetic force at its point of maximum at 

 this particular magnetic epoch, will be as perfect as could be desired. 

 With respect to its present geographical position, we may also hope 

 that Lieut. Blakiston may have an opportunity, before his employ- 

 ment is terminated, of removing any doubts that may exist as to the 

 precision of the longitude assigned to it by the survey of 1843-44. 

 It cannot have escaped notice that the 7S stations of that .survey, 

 which by their combination assigned the latitude and longitude of 

 the point of maximum, did not perfectly fulfil one important condi 

 tion regarding their distribution, viz. that of symmetrical arrange- 

 ment on all sides of the point in question. There was a considerable 

 preponderance of stations situated on the west of the meridian of the 

 point itself, and a deficiency on the eastern side, which might have 

 been remedied, had circumstances permitted, by a line of stations as 

 originally contemplated on the canoe route from Canada to Moose 

 Fort at the south-western end of Hudson's Bay, and possibly by 

 some additional stations between Moose Fort and York Fort. The 



