1^ Mr» Boner on the [JtJtt^ 



•Complement of sum ,;..; ...•• M1329 (« 



Sine of J- sum of threfe sides 18^ 21" SCV' . . . . 949837 \h 



Sine of differ, of 4- sum and side? lo ac oo noomc / 



1^ -p * ^ lo oo oo fc,,, y*ooiyo (c 



Sum of tf, h,c 2)19-99362 



Cosine ^ | = 6^ 56" 9*99681 



Therefore ^ P = 13° 52' 



•f Longitude of magnetic pole, or z M P L = 75 49 31^" 



Hence long, of place of observation 89 41 31-i- 



Lonff. observed 89 41 00 - 



DiflPerence . . . . Sl^^; 



After so perfect an agreement between observation and conT- 

 putation, I have reason to think that I had determined the true 

 place of the magnetic pole for the time of observation, and that 

 consequently it may, upon the same principle, be determined 

 for any particular time, its revolution being necessarily as regular 

 as the course of the stars. If this regularity be once irrevocably 

 established, vte shall have one side P M of the triangle, and the 

 angle M P L constantly givefi, and P R, the complement of 

 latitude, mostly without much difficulty. If then by any means 

 we can succeed in discovering the error either of the variation, 

 or the dip, we shall always have a sufficient number of data for 

 the discovery of longitude. I know that the longitudes and 

 latitudes of the magnetic pole calculated by Capt. Parry and 

 other gentlemen, a^ree with their relative variations and dip, 

 but they must be, calculated for every new observation, and every 

 new result contradicts all the preceding operations, which, I am 

 confident, is owing to an error of the compass, and not to a real 

 shifting of the magnetic pole. 



The change of position in the pole is slow and regular, and I 

 have sufficient reasons to beheve that I have not erred much 

 respecting the rate of its periodical progress, or that I have at 

 least pointed out the means of determining it. 



If this be done, the most important question will be, how we 

 may discover the errors of the compass and of the dipping nee- 

 dle, if we cannot prevent them ? I should think, that the follow- 

 ing experiment might be a means of obtaining that end, or at 

 least of facilitating our research after it. Having determined the 

 situation of the magnetic pole by the preceding table for any 

 particular time in London, and calculated the variation and dip 

 accordingly, then an observation made with a compass and dip- 

 ping needle would show, how near their quantities agree with 

 those found by calculation, and the same operation being 

 repeated, with the very same instruments, at different places, at 



