116 

 NOTE TO BOOK XIII. 



(E). p. 103. BY the discoveries related in the text, a 

 cylindrical spiral of wire through which an electric current 

 is passing is identified with a magnet ; and the effect of 

 such a spiral is increased by placing in it a core of soft 

 iron. By the use of such a combination under the influ- 

 ence of a voltaic battery, magnets are constructed far more 

 powerful than those which depend upon the permanent 

 magnetism of iron. The electro-magnet employed by Dr. 

 Faraday in his recent experiments would sustain a hun- 

 dred weight at either end. 



By the use of such magnets Dr. Faraday has recently 

 discovered that, besides iron, nickel and cobalt, which pos- 

 sess magnetism in a high degree, many bodies are mag- 

 netic in a slight degree. And he has made the further 

 very important discovery, that of those substances which 

 are not magnetic, many, perhaps all, possess an opposite 

 property, in virtue of which he terms them diamagnetic. 

 The opposition is of this kind ; that magnetic bodies in 

 the form of bars or needles, if free to move, arrange them- 

 selves in the axial line joining the poles; diamagnetic 

 bodies under the same circumstances arrange themselves 

 in an equatorial position, perpendicular to the axial line. 

 And this tendency is found to be the result of one more 

 general ; that whereas magnetic bodies are attracted to 

 the poles of a magnet, diamagnetic bodies are repelled 

 from the poles. The list of diamagnetic bodies includes 

 all kinds of substances ; not only metals, as antimony, bis- 

 muth, gold, silver, lead, tin, zinc, but many crystals, glass, 

 phosphorus, sulphur, sugar, gum, wood, ivory ; and even 

 flesh and fruit. 



