TERRESTRIAL MAGNETISM. 59 



distinguished clearly between magnetism and electricity in 

 respect to their effects, while he yet regarded both as 

 emanations of a single fundamental force inherent in all 

 matter. As is the privilege of genius, from feeble ana- 

 logies he successfully divined much. Prom the clear con- 

 ceptions which he formed of terrestrial magnetism (de 

 magno magnete tellure), he even at that time correctly 

 ascribed the origin of magnetic poles in the upright iron 

 bars of crosses on old church-towers, to impartation from 

 the magnetism of the earth. He was the first in Europe 

 who showed how to render iron magnetic by rubbing it with 

 the loadstone, which indeed the Chinese had known and 

 practised almost 500 years before.( 59 ) Gilbert also already 

 gave steel the preference over soft iron, because capable of 

 appropriating to itself and retaining more permanently the 

 magnetic force imparted to it. 



In the course of the 17th century, the navigation of 

 the Dutch, English, Spaniards, and French (which had so 

 greatly increased in extent through the improvement in the 

 means of determining the direction of a ship's course, and the 

 length or amount of distance traversed by her), augmented 

 the knowledge already possessed of different isogonic lines, 

 and more particularly of the lines of no declination, which, 

 as already mentioned, Acosta had attempted to form into a 

 system. ( 60 ) In 1616, Cornelius Schouten pointed out in 

 the middle of the Pacific Ocean, near the Marquesas, places 

 where the needle had no variation. We still find in this 

 region a singular " closed" system of isogonic lines, within 

 which the declination changes in amount in successive con- 

 centric curves. ( 61 ) The eagerness to discover new methods 

 of determining the longitude, for which it was thought not 



