THE UNIVERSE. OCEANIC DISCOVERIES. 281 



That which belongs to Columbus is not the first observation 

 of the existence of the variation (which, for example, is noted 

 in the map of Andrea Bianco in I486), but the remark 

 which he made on the 13th of September, 1492, that "2J 

 east of the Island of Corvo the magnetic variation changes, 

 passing from N.E. to N.W." 



This discovery of a ' ' magnetic line without declination" 

 marks a memorable era in nautical astronomy. It has been 

 celebrated with just praise by Oviedo, Las Casas and Herrera. 

 Those who with Livio Sanuto would attribute it to the 

 famous navigator Sebastian Cabot, forget that the first 

 voyage of the latter, made at the cost of some merchants of 

 Bristol, and distinguished by its attaining the American 

 continent, took place five years later than Columbus's first 

 voyage of discovery. But not only has Columbus the merit 

 of having discovered the part of the Atlantic in which at that 

 period the geographic and magnetic meridians coincided; 

 he also made at the same time the ingenious and thoughtful 

 remark, that the magnetic variation might serve to determine 

 the ship's position in respect to longitude. In the journal 

 of the second voyage (April 1496) we find him really in- 

 ferring his position from the observed declination. The 

 difficulties which oppose this method of determining the 

 longitude, (more especially in a part of the globe where the 

 magnetic lines of declination are so much curved that they 

 do not follow the direction of the meridian, but correspond 

 even with the parallels of latitude for considerable distances), 

 were at that period still unknown. Magnetical and astrono- 

 mical methods were anxiously sought after, in order to deter- 

 mine, both on land and sea, the points intersected by the ideally 

 constituted line of demarcation. Neither the state of science 



