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THE NATIONAL GEOGRAPHIC MAGAZINE 



the; scientific staff and crfw of thf "carnfgie'' on thf cruise from saint 



JOHNS, N. F., TO FAEMOUTH, ENGLAND, OCTOBER, I909 



In the foreground is seen one of the two special observation houses in which the instru- 

 ments are placed. The dome can be revolved and an open panel pointed to any pait of the 

 skies, thus making possible both astronomical and magnetic observations, and affording pro- 

 tection from wind and weather. 



very few, chiefly iron, steel, nickel, and 

 cobalt. The last two substances respond 

 SO feebly to a magnetic force that com- 

 passes made of them would be almost 

 as useless as those made of brass. In 

 one other respect magnetic force differs 

 in its action from that of gravity : the 

 force exerted on a magnet is not the 

 same on the two ends — equal in strength 

 and likewise parallel, to be sure, but op- 

 posite in direction. 



If, therefore, as has long ago been con- 

 cluded, it is the earth itself, as a magnet, 

 which is exerting the force we saw act- 

 ing on the compass and on the dip needle, 

 then its action is that of a couple. That 

 is to say, were we to float, as Robert 

 Norman did, over three centuries ago, a 



magnetized needle on a cork in a bowl 

 of water, then, if the liquid is not agi- 

 tated, the cork will not move from place 

 to place, but simply turn around until the 

 needle points in the direction it occupied 

 at the end of the experiment of vibra- 

 tions made above. 



VAGARIES OF THE COMPASS 



If the compass invariably points out 

 some definite direction, where does it 

 point ? To the exact north — to the 

 North Star or to the true North Pole? 

 "True as the needle to the pole," the old 

 saying has it, but. alas, considerably far 

 from the truth. In northeastern Maine 

 the compass stands 20 degrees west of 

 north ; in the northwestern part of the 



