282 EPOCHS IN THE HISTORY OF THE CONTEMPLATION OP 



nor that of the imperfect instruments employed at sea in 1493, 

 whether for measuring angles or time, were competent to the 

 practical solution of so difficult a problem. Under these 

 circumstances, Pope Alexander VI., in presumptuously 

 dividing half the globe between two powerful states, rendered 

 without knowing it an essential service to nautical astronomy 

 and to the physical science of terrestrial magnetism. The 

 great maritime powers were from that time continually 

 solicited to entertain innumerable impracticable proposals. 

 Sebastian Cabot, as we learn from his friend Eichard Eden, 

 still boasted on his death bed that there had been ' ' divinely 

 revealed to him an infallible method of finding the longitude." 

 This revelation was no other than his firm belief that the 

 magnetic declination changed rapidly and regularly with 

 the meridian. The cosmographer Alonso de Santa Cruz, 

 one of the instructors of Charles Y., undertook the drawing 

 up of the first general " Yariation Chart", ( 433 ) although, 

 indeed, from very imperfect observations, as early as 1530, 

 or a century and a half before Halley. 



The " movement" of the magnetic lines, the first recogni- 

 tion of which is usually ascribed to Gassendi, was not even 

 yet conjectured by William Gilbert ; but at an earlier period, 

 Acosta, " from the information of Portuguese navigators/' 

 assumed four lines of no declination upon the surface of the 

 globe. ( 434 ) Hardly had the inclinometer, or dipping needle, 

 been invented in England by Bobert Norman, in 1576, 

 than Gilbert boasted that, by means of this instrument, he 

 could determine the position of a ship in a dark and starless 

 night (acre caliginoso). ( 4 ^ 5 ) From my own observations 

 in the Pacific, I shewed soon after my return to Europe 

 that, in certain parts of the earth, and under particular local 



