CHAPTER I. 



DISCOVERY OF LAWS OF MAGNETIC PIIKXOMEXA. 



history of Magnetism is in a great degree similar to that of 

 J- Electricity, and many of the same persons were employed in the 

 two trains of research. The general fact, that the magnet attracts 

 iron, was nearly all that was known to the ancients, and is frequently 

 mentioned and referred to ; for instance, by Pliny, who wonders and 

 declaims concerning it, in his usual exaggerated style. 1 The writers 

 of the Stationary Period, in this subject as in others, employed them- 

 selves in collecting and adorning a number of extravagant tales, which 



o o o 



the slightest reference to experiment would have disproved ; as, for 

 example, that a magnet, when it has lost its virtue, has it restored by 

 goat's blood. Gilbert, whose work JDe Magnete we have already 

 mentioned, speaks with becoming indignation and pity of this bookish 

 folly, and repeatedly asserts the paramount value of experiments. He 

 himself, no doubt, acted up to his own precepts; for his work contains 

 all the fundamental facts of the science, so fully examined indeed, that 

 even at this day we have little to add to them. Thus, in his first 

 Book, the subjects of the third, fourth, and fifth Chapters are, 

 that the magnet has poles, that we may call these poles the north 

 and the south pole, that in two magnets the north pole of each 

 attracts the south pole and repels the north pole of the other. This 

 is, indeed, the cardinal fact on which our generalizations rest ; and the 

 reader will perceive at once its resemblance to the leading phenomena 

 of statical electricity. 



But the doctrines of magnetism, like those of heat, have an addi- 

 tional claim on our notice from the manner in which they are exempli- 

 fied in the globe of the earth. The subject of terrestrial magnetism 

 forms a very important addition to the general facts of magnetic 

 attraction and repulsion. The property of the magnet by which it 

 directs its poles exactly or nearly north and south, when once dis- 

 covered, was of immense importance to the mariner. It does not 



: Hist. Nat. lib. xxxVi. c. 25. 



