154 APPENDIX. 



at Sea-horse Point, was only a very little less than that of 

 the earth ; and consequently when these forces were opposed 

 to each other, as was the case with the ship's head south, 

 the remaining intensity upon the needle, viz.^ .19, was by no 

 means sufficient to give it any direction, and hence its power- 

 less state with the ship's head towards this quarter. But 

 with the ship's head to the north, the magnetism of the 

 earth and that of the vessel conspired together, and the 

 needle was rendered active by their joint influence, although 

 this activity was obviously useless for the purpose of navi-. 

 gation. 



These deductions will perhaps be rendered more intelli- 

 gible to some readers by means of the diagram (Fig. 3.) 

 w^hich represents the vessel swung round to the four prin- 

 cipal quarters. North, South, East, and West, the letter n 

 in the vessel indicating the point in the same which attracts 

 the north end of the needle. Now, with the vessel's head 

 east, at Green Hithe, the needle was drawn by the earth to- 

 wards N', and by the ship towards n' ; and the angle which 

 the needle assumed having been S° from o n', shows that the 

 power emanating from N' was to that proceeding from n' as 

 ab to 6c, or as sin. 82° to sin. 8°, or, as we have seen, as 7 to 

 1. But in Hudson's Bay the ratio of these two forces was, in 

 consequence of the increase of the one and the decrease of 

 the other, reduced to that of ri9 to 1 : that is, nearly to 

 equality, and consequently now, with the ship's head to the 

 true magnetic east or west, the needle ought to have stood 

 nearly north-east and north-west; but incoming round to 

 the southward, the action of the ship counteracting more and 

 more the action of the earth, as it became more directly 

 opposed to it, the needle would become more and more in- 

 active, and incapable of taking up any decided line of direc- 

 tion. With the head towards the north the ship and earth 



