Polytechnic Association Proceedings. 971 



Some knowledge of polar attraction is necessary to the study of 

 astronomy; it is of national importance, inasmuch as the direction 

 of the needle is oftentimes the arbiter of the lines and boundaries 

 of our .national domain, as it is also of our private estates; we rely 

 upon it when, in traversing the continent, we plunge into the depths 

 of the forest, and it is our only safe guide over a trackless ocean, 

 through darkness and tempest, to the haven we seek. Tens of 

 thousands of lives, and hundreds of millions of property through- 

 out the world, are every hour dependent on it for safety; any 

 inquiry therefore into its causes, and the laws which govern it, is 

 invested with an interest second to no other; and, notwithstanding 

 this, it may safely be said that, in comparsion with the whole that 

 may be known, very little is at present positively known concerning it. 



The existence of polar magnetism was first revealed to us by the 

 discovery of the compass. There is some doubt as to the exact 

 time of that discovery, but it is supposed to have been first put to 

 practical use by the early navigators in their commerce on the 

 Mediterranean sea. At that time, and long afterward, the needle 

 was supposed to tend always toward a fixed pomt in the north; 

 and therefore, when Columbus undertook his voyage of discovery, 

 he was greatly suprised and not a little perplexed to find that, as 

 he sailed westward, the needle gradually changed its direction; 

 and his crew became so much alarmed by it, that all the steadiness 

 of mind which that great navigator possessed was necessary suffi- 

 ciently to calm their fears to prevent an open mutiny, and thus 

 defeat his enterprise. In later times, by the observations of later 

 voyagers, explained by charts, together with improved instruments 

 for observation, and the means invented for determining the varia- 

 tion at any point, navigation has been made quite safe and certain 

 to the careful and skillful navigator. But, so far as I am informed, 

 the cause of these variations of the compass, and the laws which 

 govern them, are wholly unknown to science. 



I shall not detain you with a detail of the course of reasoning by 

 which I have, in my own judgment, arrived at a full conclusion in 

 this matter^ but state broadly, and at once, what that conclusion 

 is, and then explain some of the evidences on which it rests. 



The cause, then, of the variations of the compass, which some 

 have supposed to proceed from the oscillations of the earth, is, in 

 my judgment, the revolution of the magnetic pole around the 

 North pole. 



By the magnetic pole we mean that point on the earth's surface 



