APPENDIX. 155 



would conspire together to give activity to the needle, as 

 above-stated. 



Now, when the correcting plate was applied, the needle 

 was then inactive, to whatever point the ship's head was 

 directed, at least after the dip exceeded S6°|-, although it 

 had done all that was required of it before. The reason of 

 this is also sufficiently obvious, for the plate counteracting 

 the magnetic power of the vessel, the directive intensity of 

 the needle in all positions was the same, and this, as we 

 have seen, was alone insufficient to give it direction. In the 

 preceding voyage of the Griper, under the command of 

 Captain Clavering, the greatest observed dip was 81°^, and 

 the plate was effective throughout. In the present case it 

 was found efficient till the dip amounted to 86°;^, but this 

 appears to be its limit, for beyond this the intensity of di- 

 rection was so small as to be incompetent to overpower the 

 friction on the point. 



It will be observed that all the above inferences are drawn 

 from the single shore observation at Sea-horse Point, but as 

 from these it appears the magnetic pole was then to the 

 south-west, and distant less than 7° ; and as the vessel 

 afterwards continued to advance nearly 3° in a line bearing 

 directly towards it, there can be no doubt the dip continued 

 to increase, and that at the most northern and western part 

 of the voyage the dip was at least 87-^°, while the variation, 

 if our preceding determinations are to be relied on, was re- 

 duced to almost nothing. Hence the reason, in the first 

 place, of all the observed irregularities getting greater as 

 the latitude increased ; and secondly, in consequence of a 

 probable decrease of at least three points westerly variation, 

 these irregularities would appear more easterly than before, 

 for as there was no means of estimating directions except by 

 the true meridians, and the variation having been more than 



