No. IV. 



REMARKS ON TABLE, No. VII. 



633 



General Remarks on the Variation of the Compass, observed during our Journey in North 

 America, and along the Arctic Sea. — The Compasses used were of Captain 

 Eater's improved Construction. 



The results of the observations obtained in Hayes, Steel, and Hill Rivers, (lying 

 between the latitudes 57° 00' N., and 55° 14' N., and longitudes 92° 26' W., and 

 94° 22' W.,) were so very variable, that no inferences can be drawn from them as to 

 any proportionable increase or decrease of variation in advancing to the westward ; 

 and it would be difficult to assign any cause for these irregularities in the two lower 

 rivers, whose banks are entirely composed of alluvial soil. The rocks in Hill River 

 occasionally contained magnetic iron ore. 



As we advanced to the westward from Hill River to Carlton, (latitude 52° 51' N., 

 and longitude 106° 3' W.,) we found the easterly variation to increase in the mean 

 ratio of fifty-two minutes for each degree of longitude. I am of opinion, that this 

 augmentation of the variation was not owing to the small angle which our route 

 made to the southward. From Carlton we advanced to the northward, by Isle a la 

 Crosse to the Methye Lake, and found that the -variation did not increase with the 

 latitude ; which confirmed me in the opinion just stated, that in these parallels the 

 variation was not affected by a change of latitude ; or in other words, that the lines 

 of variation run nearly north and south in that quarter. In proceeding from the 

 Methye Lake down the Clearwater River, which runs from east to west, an increase 

 of variation was observed, nearly equal to what occurred in a similar change of lon- 

 gitude, farther to the southward; but in descending the Athabasca River, upon 

 nearly a north course, the variation decreased a degree and half, notwithstanding a 

 small increase of westerly longitude. 



We had not an opportunity, during the descent of Slave River, of making a suffi- 

 cient number of observations to ascertain whether the variation increased regularly 

 with the longitude; but at Moose Deer Island, (bearing N. 26° W., 168 miles from 

 Fort Chipewyan,) the variation was found to be 2° 51' greater than at the latter 

 place. 



After leaving Moose Deer Island, and proceeding to the northwards across Slave 

 Lake, the variation, contrary to the law it had hitherto followed, increased with an 

 increase of latitude. At an island adjoining to Isle la Cache of Mackenzie, (bear- 

 ing N. 20° E , forty-two miles of Moose Deer Island;) the variation was 5° 20' 

 greater ; and at Fort Providence, bearing N. 40° W., and thirty-five miles from the 

 latter place, a farther increase of 2° 33' was observed ; making, at that place, a total 

 of 7° 55' E. The fishermen at Fort Providence occasionally collect pieces of magnetic 

 iron ore in their nets, and it is probable that the same ore may occur among the 



4 M 



