MAGNETISATION. 57 



bastian Cabot, and Vasco de Gama, were not acquainted 

 with the log and its mode of application, and they 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 period 

 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 deter- 

 mined 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 afterwards, that attempts were made to 

 measure 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. 58 

 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 

 results from feeble analogies, and the clear views which he 

 had taken of terrestrial magnetism (de magno magnete 

 tellure) led him to ascribe the magnetisation 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, although the Chinese had been aware of the fact 

 nearly 500 years before him. 59 Even then, Gilbert gave 



58 Cosmos, vol. i, p. 170. Calamitico was the name given to these 

 instruments in consequence of the first needles for the compass 

 having been made in the shape of a frog. 



59 See Gilbert, Physiologia Nova de Magnete, lib. iii, cap. viii, p. 124. 

 Even Pliny (Cosmos, vol. i, p. 170), remarks generally, without, how- 

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

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

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

 " vulgiris opinio de montibus magneticis aut rupe aliqua magnetica, de 

 polo phantastico a polo mundi distante" (1. c. p. 42 98). The variation 

 and advance of the magnetic lines were entirely unknown to him. 

 ' Varietas uniuscujusque bci constana est" (1. c. 42, 98, 152, 153. 



