50 TERRESTRIAL MAGNETISM. 



remains ever the same. The investigation of the dominion 

 of law amidst variability, is itself the proximate object, or 

 the goal immediately aimed at, in every investigation into a 

 force in nature. "While the labours of Coulomb and Arago 

 have demonstrated that the electro -magnetic process can be 

 elicited in the most various substances, Faraday's brilliant 

 discovery of diamagnetisin, on the other hand, shows us 

 here also, in the distinction of north and south axiality in 

 one class of substances, and east and west axiality in 

 others, that influence of the diversity or heterogeneity of 

 substances of which molecular or mass-attraction is wholly 

 independent. Oxygen gas, enclosed in a thin glass tube, 

 when placed under the action of a magnet in its vicinity, 

 assumes " paramagnetically" a north and south direction, 

 like iron; nitrogen, hydrogen, and carbonic acid gas, 

 remain unaffected ; while phosphorus, leather, and wood, 

 under the same circumstances, range themselves "dia- 

 magnetically," i. e. in an equatorial or east and west 

 direction. 



The facts known in Greek and Roman antiquity were : 

 the adhesion of iron to the loadstone ; magnetic attraction 

 and repulsion ; the propagation of the attracting influence 

 through iron vessels, and also through rings ( 52 ) forming 

 links in a chain (one ring being in contact with the load- 

 stone) ; and the non-attraction of wood, or of other metals 

 than iron. Of the polar directive force which magnetism 

 could impart to a body susceptible of its influence, the 

 early western nations (Phoenicians, Etruscans, Greeks and 

 Romans) knew nothing. It is not until the llth and 12th 

 centuries of our era that we find among the European 

 nations any knowledge existing of this " directive force," 



