972 Transactions of the American Institute. 



within the arctic ckcle to which the needle points. By the North 

 pole we mean« of course, the polar axle of the earth on which she 

 tui-ns in her diurnal revolution. And by the variations of the com- 

 pass, we mean the divergence of the needle's point east or w^st, from 

 the true north point, with its variableness at different times and in 

 different places. 



The revolution of the magnetic pole occurs gradually, through 

 a long period of time, and, according to the best data which I can 

 obtain, is completed only once in about six hundred and forty 

 years. The time may be found to be somewhat longer or shorter, 

 when settled by accurate observation. 



The exact position of the magnetic pole has never been accu- 

 rately known. It is known, however, to be at present situated on 

 the North American continent, in a high latitude, and considerably 

 west of the longitude of New York. This was made manifest by 

 the observations of Captain Eoss in his polar expedition. He 

 placed the magnetic pble in latitude about 70 deg. 30 min. north, 

 and longitude 96 deg. west from Greenwich. It has changed con- 

 .uderably since that time, and is at present both farther north and 

 farther west than he placed it.* 



The variation of the compass from the true north point at London 

 or Greenwich is at present westerly. At New York it is still west- 

 erl}^ in a less degree, and at the islands in the Pacific Ocean it is 

 easterly. Now, if the accurate variation at each of these points be 

 taken (all local attractions being absent), and lines in the direction 

 of the needle be produced northerly, they will meet at a point not 

 far fi-om 76 deg. north latitude, and 118 deg. west longitude from 

 Greenwich. And that point, wherever they do meet, may safely 

 be affirmed to be the present position of the North magnetic pole. 

 It is not necessary for our present purpose that we should fix the 

 exact point, nor are the means at hand to do it if needed — it must 

 be done by careful and repeated observations at the same time on 

 different and widely separated meridians, so as to exclude all pos- 

 sibility of error, 



* That Captain Ross did not quite reach the pole, is, I think, self-evident; because, 

 if the situation of the pole had been in 70 deg. 30 min. north, and longitude 96 deg. west, 

 it would have given a greater variation at London than existed at that time. But that 

 tis was the nearest approximation to the truth ever before known, is nevertheless quite 

 certain. Almost at the same period of time, Humboldt placed it in his estimation in 

 latitude 79 deg. north, and longitude 27 deg. west from Greenwich. This was certainly 

 very far from the truth, as the observations of Capt. Ross, and all other authentic facts, 

 conclusively show. For myself, I am unable to perceive on what basis of known truths 

 Humboldt could have grounded his opinion. 



