MAGNETIC REPULSION. 51 



difficulty "why the vortex which circulates around the 

 lodestone does not make its way to wood or stone as well 

 as iron," and, again like Descartes, answers, that "the 

 pores of the iron have an analogy to the particles of the 

 vortex circulating about the lodestone which yields them 

 such access as they can find in no other bodies whose pores 

 are differently formed." 



Plutarch also refers to magnetic repulsion and says that 

 "like as iron drawn by a stone often follows it, but often 

 also is turned and driven away in the opposite direction, 

 so also is the wholesome good and regular motion of the 

 world." 



It must not be assumed, because of the interpretations 

 which it is possible to make at the present time of the 

 magnetic phenomena mentioned by lyucretius, that any 

 actual knowledge of the polarity of the lodestone existed 

 in his day. Not until centuries later did this come to the 

 civilized world. 



Even when in course of time the recurrence of the re- 

 pelling effect of the magnet attracted attention, no concep- 

 tion of polarity resulted. On the contrary, it was for a 

 long time believed that the stone which repelled was a 

 totally different stone from that which attracted iron. 

 This supposed repelling stone is described for the first time 

 by Pliny, 1 who calls it the "theamedes" and says that it 

 comes from "Ethiopia, not far from Zmiris." For the 

 first thirteen .centuries of our era, belief in its existence 

 was implicit. It served conveniently to explain mag- 

 netic repulsion, and hence, as frequently happens in such 

 circumstances, it prevented investigation of that effect. 



For discoveries concerning the amber, search may now 

 be made through many centuries in vain. Plato, as has 

 been stated, had linked together the attraction of the 

 amber and the Heraclean stone, and Epicurus had attrib- 

 uted both to the same cause, namely, atoms and invisible 



1 Pliny: lib. xxxvi. 25. 



