58 • cosmos. 



estimated the ship's speed merely by the eye, while they found 

 the distance they had made by the running down of the sand 

 in the glasses known as ampolletas. For a considerable pe- 

 riod the horizontal declination from the north pole was the 

 only element of magnetic force that was made use of, but at 

 length (in 1576) the second element, inclination, began to be 

 first measured. Robert Norman was the first who determ- 

 ined the inclination of the magnetic needle in London, which 

 he noted with no slight degree of accuracy by means of an 

 inclinatorium, which he had himself invented. It was not 

 until 200 years afterward that attempts were made to meas- 

 ure the third element, the intensity of the magnetic terrestrial 

 force. 



About the close of the 16th century, William Gilbert, a 

 man who excited the admiration of Galileo, although his 

 merits were wholly unappreciated by Bacon, first laid down 

 comprehensive views of the magnetic force of the earth.* 

 He clearly distinguished magnetism from electricity by their 

 several effects, although he looked upon both as emanations 

 of one and the same fundamental force, pervading all matter. 

 Like other men of genius, he had obtained many happy re- 

 sults from feeble analogies, and the clear views which he had 

 taken of terrestrial magnetism (de magno magnete tellure) 

 led him to ascribe the magnetization of the vertical iron rods 

 on the steeples of old church towers to the effect of this force. 

 He, too, was the first in Europe who showed that iron might 

 be rendered magnetic by being touched with the magnet, al- 

 though the Chinese had been aware of the fact nearly 500 

 years before him.f Even then, Gilbert gave steel the pref- 

 erence over soft iron, because the former has the power of 

 more permanently retaining the force imparted to it, and of 

 thus becoming for a longer time a conductor of magnetism. 



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



* Cosmos, vol. i., p. 177. Calamitico was the name given to these 

 instruments in consequence of the first needles for the compass hav- 

 ing been made in the shape of a frog. 



t See Gilbert, Physiologia Nova de Magnete, lib. iii., cap. viii., p. 121. 

 Even Pliny (Cosmos, vol. i., p. 177) remarks generally, without, how- 

 ever, referring to the act of touching, that magnetism may be impart- 

 ed for a long period of time to iron. Gilbert expresses himself as 

 follows in reference to the vulgar opinion of a magnetic mountain: 

 " Vulgaris opinio de montibus magneticis aut rupe aliqua magnetica, 

 de polo phantastico a polo mundi distante" (1. c. p. 42-98). The va- 

 riation and advance of the magnetic lines were entirely unknown to 

 him. " Varietas uniuscujusque loci constans est" (1. c. 42, 98, 152, 

 153). 



