THE MOST CURIOUS CRAFT AFLOAT 



229 



His works and our fellow-creatures in 

 all the different corners of the world," 

 etc., he goes on to say : 



"I hope that I shall be excused for 

 this short digression, it being only the 

 result of my feeling, when I conceived 

 that the longitude might be found by 

 magnetism (with the improvements 

 which I have made upon it) without any 

 trouble or calculation, and with as much 

 certainty at sea as any other way now in 

 use." Alas for Ralph Walker's fond 

 hopes ! In spite of his "improvements" 

 upon the Supreme Architect's magnet- 

 ism, we have not yet been able to find 

 the longitude at sea so simply as he 

 hoped, nor have we been able to make 

 use of his elaborate "Tables of Varia- 

 tion." 



THE earth's magnetic poles 



The earth, far from being magnetized 

 in the simple manner above supposed, is 

 instead most irregularly magnetized, the 

 distribution of land and water evidently 

 playing an important role. In place of 

 the magnetic poles being on opposite 

 sides of the earth, the North Magnetic 

 Pole is in about latitude 70° north and 

 longitude 97° west, and the South Mag- 



f^-^ 



-^ 



'^■■>\ 



' *V- - 



mmm 



mmL 



NATIVE HOUSE: PUNTA GORDA, BRITISH 

 HONDURAS 



CATHEDRAE ENTRANCE: HUEHUKTE- 

 NANGO, GUATEMALA 



netic Pole is approximately in latitude 

 2^° south and 156° east. Draw a 

 straight line connecting the two poles 

 and it will pass through the earth 750 

 miles off from the center. No formula 

 has as yet been found which, even if we 

 knew the exact positions of the two mag- 

 netic poles, could give the direction of 

 the compass at any point of the earth 

 sufficiently close to satisfy the demands 

 of the navigator and the surveyor. 



Hence, instead of mathematical tables, 

 charts must be supplied to the mariner 

 showing him, wherever he is likely to go, 

 just how the compass points. But, to 

 construct these charts, some one must 

 have found previously, by actual obser- 

 vation, the relation or angle between the 

 true north and the magnetic or compass 

 north. The mariner knows these charts 

 by the name of "Variation Charts," 

 and the lines drawn on them as, "Lines 

 of Equal A^'ariation," which connect all 

 places where the "variation" or compass 

 direction is the same, just as the iso- 

 thermal lines on a weather map join the 

 places of the same temperature. The 



