GILBERT'S ERROR IN COMPASS VARIATION. 367 



Now back to England, where we left Barlowe and Ridley 

 ''animadverting" upon one another over their respective 

 claims to Gilbert's experimental discoveries : and the 

 navigators trying to turn Gilbert's nautical instruments to 

 practical account. But the last were of no avail. Gilbert 

 had made a fundamental error as to compass variation ; 

 "that the arc thereof continues to be the same in what- 

 ever place or region, be it sea or continent, and is forever 

 unchanging." It was, however, soon detected, not by an 

 Englishman, but in all probability by Gian Francesco 

 Sagredo, who was Venetian Consul at Aleppo in about 

 1610, and who was then making observations himself 

 there, and having others do the same, at Goa in India. 

 Vastly important as this subject was to the English sailors 

 and merchants for the safety of their ships and the suc- 

 cess of their enterprises ultimately depended upon the 

 truth of their steering-needles little more than rumors of 

 the changes in local variation seem to have reached the 

 country for many years. Burton sums up, in a curious 

 blending of the old legends of the magnetic rocks with the 

 results of the new experimental observations, probably all 

 that was then known. He asks whether there be a great 

 rock of lodestone which may cause the needle in the com- 

 pass still to bend that way, and what should be the true 

 cause of the variation of the compass. 



"Is it a magnetical rock, or the pole star as Cardan 

 will ; or some other star in the bear, as Marsilius Ficinus ; 

 or a magnetical meridian, as Maurolicus ; vel situs in vena 

 terrcz, as Agricola : or the nearness of the next continent, 

 as Cabseus will; or some other cause, as Scaliger, Cortesius, 

 Conimbricenses, Peregrinus contend ; why at the Azores 

 it looks directly north, otherwise not? In the Mediter- 

 ranean or Levant (as some observe) it varies 7 grad. \ by 

 and by, 12, and then, 22. In the Baltic Seas near Rasce- 

 burg in Finland, the needle runs round if any ships come 

 that way, though Martin Ridley write otherwise that the 

 needle near the Pole will hardly be forced from his direc- 



