TERRESTRIAL MAGNETISM. 255 



and vapours, which appear to exist, relatively to each 

 other, sometimes in the one, and sometimes in the other 

 condition.* 



To endeavour to reduce our knowledge of these facts 

 to some practical explanation, we must bear in mind 

 that particular spaces around the north and south geo- 

 graphical poles of the earth, are regarded as circles to 

 which all the magnetic lines of force converge. Under 

 circumstances which should prevent any interference 

 with what is called ferro-magnetic action, all , bodies 

 coming under that class would arrange themselves ac- 

 cording to the laws which would regulate the dispo- 

 sition of an infinite number of magnets, free to move 

 within the sphere of each other's influence. The north 

 and south pole of one magnetic body would attach itself 

 to the south and north pole of another, until we had a 

 line of magnets of any extent ; the two ends being in 

 opposite states, like the magnetic points of convergence 

 of the earth. 



Every body, not ferro-magnetic, places itself across 

 such a line of magnetic force as we have conceived ; and 

 if the earth were made up of separate layers of ferro- 

 magnetic and diamagnetic bodies, the result would be 

 the formation of bands at right angles to each other. 

 This is not the case, by reason of the intermingling of 

 the two classes of substances. Out of the known che- 

 mical elements we find only about ten which are actively 

 ferro-magnetic ; the others combining with these give 

 rise to either a weaker state, a neutral condition, or the 

 balance of action is turned to the diamagnetic side. 

 Sulphate of iron, for instance, is a magnetic salt; but 



* On the Diamagnetic conditions of Flame and Gases, by Michael 

 Faraday, F.H.S. ; and On the motions presented by Flame when 

 under Electro-Magnetic Influence, by Professor Zanclcteschi. 

 Philosophical Magazine, lb'47, pp. 401421. 



