THE NAMING OF THE MAGNET POLES. 175 



of the needle which touched the south part of the lode- 

 stone must have acquired north polarity, and, therefore, 

 have pointed to the south, which is exactly the reverse of 

 what he states. True, the doctrine of similitudes would 

 lead him to infer that the north pole of the magnet would 

 point to the north pole of the heavens; but why should he 

 allow that theory to control his ideas in the face of this 

 particular demonstrated fact, when he has no hesitation 

 in stating conclusions drawn from other facts in the same 

 series of experiments, which were directly in the teeth of 

 that theory ? Two reasons may be given to account for 

 this. The first is that .the error was not due to Peregrinus, 

 but to a transposition of terms by some copyist. 



The second and stronger reason becomes clear when it 

 is remembered that the doctrine of similitudes was more 

 commonly applied with reference to the magnet and 

 needle than with reference to needle and Pole star. The 

 end of the needle in the compass was always rubbed by 

 one and the same end of the magnet, and thereafter it 

 turned to the north. Therefore it was concluded a priori 

 that the pole of the magnetizing lodestone must also be 

 north. Peregrinus undoubtedly, as others had done, 

 rubbed the north end of his magnet to the needle and 

 saw the latter point to the north, and thus, as he supposed, 

 he established the principle, not by theory, but by actual 

 experiment. And that the prevailing theory harmonized 

 with the experiment tended, of course, still further to sup- 

 port the latter. 



If he had presented to the supposed north pole of the 

 needle the south pole of the magnet, he would have seen 

 repulsion instead of attraction, and possibly have been led 

 to question his hypothesis; but that is asking altogether 

 too much of an investigator of the thirteenth century. In 

 that he experimented on the subject at all connotes im- 

 portant progress. To suggest that he might have experi- 

 mented to test the apparently plain conclusions of observa- 

 tion, is simply to impute to him a capacity for inductive 

 reasoning far in advance of his ao;e. 



