GILBERT'S MAGNETIC DISCOVERIES. 289 



netism, and disposes itself in the line of a great circle 

 passing through the poles ; or, in other words, in a mag- 

 netic meridian, a term also first used by Gilbert. 



That iron or steel acquires magnetism from the lodestone 

 and is thus itself a magnetic body, capable of attracting 

 the stone as the stone attracts it, so that the two come 

 together by forces mutually exerted, and not by the one- 

 sided attraction of magnet on object. This was, to some 

 extent, pre-suggested by Cardan, and, long before him, by 

 St. Thomas Aquinas and Cardinal de Cusa. 



That the magnetic force moves from one end of an iron 

 rod to the other. It travels through all bodies, he says, 

 and is continued on by them. Here was the first notion 

 of magnetic conduction ; the first suggestion of the pos- 

 sible movement of the force from point to point. 



That magnetization of iron occurs with great rapidity. 

 1 'It is there in an instant," he asserts, u and is not intro- 

 duced in any interval of time, nor successively, as when 

 heat enters iron, for the moment the iron is touched by 

 the lodestone it is excited throughout." 



That the lodestone most strongly attracts the best and 

 purest iron that the best iron is derived from the lode- 

 stone or magnetic ore that the strongest magnets are 

 made from the best iron and that the best iron, even if 

 not magnetized, acts like the lodestone in directing itself 

 to the earth's poles, through induction from the earth. 



That iron can be magnetized by simple placing in the 

 plane of the magnetic meridian or, better, by being 

 hammered or wire-drawn, or heated and cooled while so 

 disposed ; and that maintenance of a magnet in the same 

 plane conserves its properties. Thus Gilbert says that 

 iron bars which have been fixed in buildings for twenty 

 years or more in north and south position acquire ver- 

 ticity, and thus he explains the magnetization of the iron 

 rod taken down from the church of St. Augustine in 

 Rimini ; a phenomenon which Giulio Cesare had accident- 

 ally remarked several years before. There is a world of 

 19 



