ELECTRO-MAGNETISM. 441 



idly, the muscles are closed so firmly, that the handles can not be dropped, 

 and most powerful convulsive shocks are sent through the arms and body. 



What isadia- 819. It has been demonstrated by Professor 

 magnetic body? Faraday that bodies, not in themselves mag- 

 netic, may, when placed under certain physical conditions, 

 be repelled by sufficiently powerful electro-magnets. Such 

 substances have been termed diamaguetic, and the phe- 

 nomena developed have received the general name of dia- 

 magnetism. 



Bodies that are magnetic are attracted by the poles of 

 a magnet ; bodies that are diamagnetic are repelled by 

 the poles of a magnet. Magnetism may be regarded as 

 an attractive force, diamagnetism as a repelling one. 



Thus, if a bar of iron is suspended free to move in p^^ 



any direction, between the poles, N S, of a magnet. 

 Fig. 373, the bar will arrange itself along a line 

 which will unite the two poles ; it places itself in the 

 axial line, or along the line of force. Such is the con- 

 dition of a magnetic body. If a substance of the diamagnetic class is placed 

 „ ^^. in the same situation — as, for example, a bar of bis- 



muth — between the poles, N S, Fig. 374, it places it- 



^^ self across, or at right angles to the axial line, or the 



^^m ^® of force. 



^^^ Every substance in nature is in one or the other of 

 these conditions. " It is a curious sight," says Dr. 

 Faraday, " to see a piece of wood, or of beef, or an apple, or a bottle of water 

 repelled by a magnet ; or taking the leaf of a tree, and hanging it up between 

 the poles, to observe it taking an equatorial position." 



19' 



