10 Mr, Boner onthe [JutT, 



variation will be 24° 40^ 31'^; the dip 72° 04' 44'', and the Ion- 

 gitude of the magnetic pole 70° 12' 52", its latitude 74° 56' 32". 



When I say that these things are to take place, it will be 

 understood oi course that I do not pretend to affirm it positively, 

 but only so far as the observations which I have made subser- 

 vient to corroborate my theory, are correct. So much, I am 

 confident, is true, that the annual progress cannot differ much 

 from what I have stated it to be, and that in every case it will 

 be found dependant on some one of the astronomical periods 

 which I have mentioned. An inquiry into the cause of variation 

 seems therefore to be a subject as much deserving the atten- 

 tion of the astronomer as that of the tide and the monsoon, with 

 both of which it is probably connected. The result of his obser- 

 vations being every year inserted in the Nautical Almanac, 

 would, I should think, be of material service to the mariner. I 

 need not say, how easy it would be to find the longitude, if we 

 could depend on the exactness of the dip and variation, as this 

 must be obvious to every mathematician. It is therefore of the 

 greatest importance, that we should learn to determine the true 

 dip and variation, though the instruments made use of should 

 not be quite perfect, in the same manner as we may know the 

 exact time of the day by means of an incorrect watch, as soon as 

 we are acquainted with its defects. 1 have been told that the 

 dip cannot be depended on so much as the variation ; but on 

 examining a series of observations made by Capt. Parry and 

 Capt. Lyon, I find to the contrary the dip almost constantly very 

 nearly, what I should have expected it to be, whilst the variation 

 bears not the least resemblance to truth ; for I see it constantly 

 west, when I had every reason to think it would have been east. 

 The only way of accounting for this contradiction is to suppose 

 that the poles of the needle have been changed, a fact which I 

 have often witnessed myself; and concerning the reality of 

 which the following passage, taken from the Imperial Encyclo- 

 paedia, will remove every doubt : — 



" Although magnetic attraction generally takes place only 

 between the opposite poles of two magnets, yet it often happens 

 that though the north' pole of one magnet be presented to the 

 north pole of another, that they show neither attraction nor 

 repulsion; but that wheii placed very near each other, they will 

 attract. For it often happens that one of the magnets^ J)eing 

 more po>verful than the other, will chaage the pcle of that o^her 

 magnet, and then _ au atUjaction will take [)Lice betvve^i^ ,two 

 poles apparently of* tbe'^sanie name, though m ,t^^ .i!ilA^,.an 

 attraction between poles of difFerent names, because one of them 

 has actually J>een changed." h2 ^80 *^til = 171 *^I 9fli8 



Confvwie^-*^ 4^y PP^".^^"^ ^y *^ passagitf, i cdTidli^fi^ that if 

 the poles-D£ the' needle had exchanged places, that end of it 

 which, l^thoutisuch a change, would have pointed eastward, 



