1325.] Variation of the Mariner* s Compass, 11 



must now necessarily point westward, and that to judge rightly 

 of the variation, we ought to make it equal to the supplement of 

 that marked by the compass, and call it by a contrary name. 

 Experience, however, did not quite answer my expectations ; 

 for in the first example, where 1 supposed the variation would 

 turn out to be 61° 44' E, being the supplement of 118° 16^ W; 

 computation gave only 53° 50' 26" ; that is, nearly eight degrees 

 less ; but the dip was only 38' 36" less than that by observation. 

 Suspecting now that the dip observed might be nearly correct, 

 and having little doubt but that the longitude and latitude of 

 the magnetic pole, calculated for the time of observation by the 

 table ot mean annual motion; namely, 38' 20" 47'''-28, would 

 not be far from the truth, 1 concluded that the dip, with the lati- 

 tude of the place of observation, would suffice to find the longi- 

 tude in spite of. the irregularity of the compass and of time- 

 keepers, without any astronomical observation but what was 

 requisite for the finding of latitude. The result was satisfactory 

 beyond all expectation ; the difference of longitude observed and 

 that by computation being but half a minute* , . l e:iij> 



Observations from Capt . Lyovis last Voyage, ' * ed^ .;* ' '^^ 



1820.— Regent^s Inlet, Latitude . ) .C! ) . . 72° ^S^^ff '^^l 

 '?^t ^Iff / > Longitude 89 41 W^ r 



. ^ ,. ,-; as?, dfl. ^ Dip j ^8 26 1 



ii;q,jx,«o;^i variati^.';;K/|^p^ i|S^^;:' 



Computed lafitiide of magnetic pole. '/^'^^'"^j^ 10 

 Computed longitude of ditto ;i i'^^^^8 16 



Supposing the longitude unknown, how could it be found by 

 these data, of which the three last, owing to the irregularity of 

 the 5i04)^p^ji^, are^ positively, wrong? _ 



P M, complement of latitude „„_- jfJxjob viavs r 



of magnetic pole iMoPSSe m9h^,:.(^L^.^^^- . , 



P R, complement of latitudefj owJlo asloq ai^&«ftro?rf:t iiis'-vl^ 



of Regent's Inlet .„ .j7o 'il%lo^ril?on ofilii^uoaf h*'^ 



M R, double complement oi/^^di Udi .ladioniJ ^;o alo | i^-' 

 ' "^>P(SR*"^t^^^4,?Sr,#^'p#^i^^)ogaq ^^w 3Bib fud ' nobr 



' Pt, meridian iif'Lon^n,'anH'liiP''^^^^^ ''"^ 



MPL, longitude of magnetic pole in 1820 at'O^'^^.S'/^p" 47-W28 

 annual progression =75° 49^ 31i-"^ its latitude considered an 

 invariable quantity =? 74° 5& 32". , , . 



- ■ iifilo 9ii(j .j.usiOd^ ,e.:-- ' io 26loq nasw ^ad aor )/-,/ 



! ' SinePM = 15^ 03' 28" . .v^9gq^4^ ^35414^*"^^^ 



iiditefeje^^oi ;!^i' m 40 ^,^^v^p,\. 9-47209 " 



>bp9 iBilJ ^830isl^ L^gnBfbxs bed albso __^^ - 



