570 SPECIAL METHODS OF DISCOVERY. 



continual inclination towards the point, ping, or . south.' l 

 It was by observation ttiat Kobert Norman discovered, in 

 1576, the dip of a magnet. Julius Caesar, a surgeon at 

 Eimini, observed in the year 1 590, that iron was converted 

 into a magnet by position alone. Professor Gunter, of 

 Grresham College, was the first to observe, in the year 

 1622, the change of declination of a magnet in the same 

 place. Gassendi also, by means of observation, discovered 

 about the year 1630, that an iron bar which had long 

 remained in one position, and had been struck by light- 

 ning, had become a magnet. In the year 1 633, Gallibrand 

 discovered by observation that the amount of variation of 

 the magnetic needle at London was not constant. Professor 

 Wargentin observed, in the year 1750, that the northern 

 aurora affected the magnetic needle. In 1778, Brugmans 

 discovered by experiment and observation, that bismuth 

 and antimony were each repelled by the poles of a magnet. 

 About the year 1805, Komagnesi observed that a magnet- 

 ised needle experiences a declination when submitted to 

 the action of a voltaic current. 2 In 1806, Humboldt, at 

 Berlin, observed and discovered the existence of magnetic 

 storms. Arago was the first to observe and discover, in 

 1824, the retarding influence of substances, metals in 

 particular, upon the movements of an adjacent magnetic 

 needle. By means of observation, comparison, and infer- 

 ence, Sabine, in 1851, discovered that the sun is a great 

 magnet, and magnetises our earth, because the terrestrial 

 magnetic force has periods respectively of 24 hours, 365 

 days, and 10 solar years. 3 



1 See Sir W. Snow Harris, Rudimentary Magnetism, part iii. p. 80 ; 

 Davis, The Chinese, pp. 277, 278 ; also Mrs. Somerville, Connexion of the 

 Physical Sciences, 2nd edit. p. 334. 



2 See Manuel du Galvanisms, par Joseph Izarn, Paris, 1805, p. 120 ; 

 also Journal of the Society of Arts, April 23, 1858, p. 356. 



3 See Encyclopedia Britannica, 8th edit., art. ' Magnetism,' p. 18. 



