No. IV.] 



639 



REMARKS ON THE DIP OF THE MAGNETIC NEEDLE. 



Previous to our departure from London the instrument was compared, and found 

 to agree with an excellent dipping-needle belonging to Henry Browne, Esq., of Portland 

 Place, which was afterwards used on Captain Parry's late Expedition to the Polar Sea. 

 One of the sides of our needle was marked with a + , and it was balanced with that 

 mark towards the observer, in which position it hung when the single observations 

 given in the subsequent Table were made ; but, whenever two results are put down, 

 the needle was inverted, and it is to be remembered the upper one is the dip shewn 

 with the marked side towards the observer. The initials B., H., F., indicate by whom 

 the observations were made, and the mean result is given. 



The observations made at York Factory, Norway House, and Cumberland House, 

 shew an increase of dip in proceeding to the south-west. Mr. Hood's observation 

 made in the spring at Cumberland House, compared with mine of the preceding 

 autumn, shew an increase of 1° 32' 48' in that interval. At Isle a la Crosse, bearing 

 about W.N.W. from Cumberland House, the dip was found by Mr. Hood to be less 

 than at Cumberland House ; but beyond that place we found that the dip increased 

 with the latitude, whether our course laid to the eastward or westward of the 

 meridian. It is to be observed, however, that the places where observations were 

 made, were perhaps too distant to enable us to deduce any general law. The great 

 dip observed at Point Turnagain, would appear to evince the proximity of that station 

 to the magnetic pole. 



The column of differences produced by changing the face of the instrument 

 exhibits a remarkable variation in these differences connected in some manner with 

 the place of observation, and which have not been noticed I believe by any previous 

 observer. I leave to others better informed on these matters than myself, to deter- 

 mine whether they ought to be ascribed to local causes, to some defect in the instru- 

 ment, or to a general law of magnetism. 



The dip was always greatest when the face of the instrument being to the west, 

 the needle hung with the marked side to the observer ; and least when the marked 

 side was from the observer, the instrument still facing to the west. The dips, when 

 the instrument was faced east, were intermediate between these extremes ; but in 

 this case, when the marked side was turned to the observer, it was less than when 

 turned from him, which is contrary to what is stated above, as taking place when 

 the instrument was faced west. These facts may, perhaps, be deemed to indicate 

 some defect in the balancing of the needle, or in the correctness of the pivots upon 

 which it turned. 



