Contemporary Advances in Physics — XIII. 

 Ferromagnetism 



By KARL K. DARROW 



Magnetism was revealed to Europeans by pieces of a mineral later 

 to be called lodestone, which lay scattered in the fields of Magnesia in 

 Asia Minor, and were endowed with the curious power of attracting 

 iron. They who first noticed it were apparently Greeks of the period 

 before the practice of writing; for legends of the discovery were trans- 

 mitted by the Greeks of later centuries, legends entangled with tales 

 of Cretan shepherds and the myth of Medea. Electricity was dis- 

 closed, evidently in the same dim period and region, by fragments of 

 amber on which friction conferred the remarkable power of attracting 

 shreds and flakes of light materials. 



By these quaint phenomena electricity and magnetism were disclosed 

 to the European world before the beginnings of written history ; and the 

 intimations were recorded in writings of classical antiquity, and handed 

 down from generation to generation. Yet two millennia and more 

 were destined to flow past, before sufficiently many further data should 

 be gathered to make possible the forming of a valid conception of 

 either. The nineteenth century arrived, before anyone detected the 

 signs that the two are but difl^erent aspects of one fundamental entity. 

 Obviously the early hints were not sufficient; but it would not be well 

 to conclude that therefore the Greeks were unwise. If they are in- 

 dicted for stupidity because they did not understand the lodestone and 

 the electrified amber, the indictment lies also against ourselves. For 

 these are instances of ferromagnetism and of frictional electricity; 

 which is to say, they belong to provinces which to this day are not fully 

 incorporated into the empire of the theory of electricity and mag- 

 netism. 



How then does it happen that the phenomena earliest discovered 

 must still be listed among the least well understood? There is nothing 

 unusual in this. There is no general reason for expecting that the 

 phenomena which occur spontaneously and frequently and conspicu- 

 ously in Nature should be the easiest to understand. On the contrary, 

 it frequently happens that they are much less instructive and inter- 

 pretable than others which can be brought to pass only by careful 

 choice of conditions and skilful experimentation. The history of 

 physics abounds in instances of such contrasts, and there is none more 

 striking than the one with which I am to deal. Many phenomena of 



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