MAGNETISM AND ELECTRICITY. 239 



copper wires which complete the circuit of a galvanic 

 battery, will attract and hold up large quantities of iron 

 tilings, and the wires of the electric telegraph will do 

 the same, while any signal is being conveyed along 

 them. Again, all the phenomena common to galvanic 

 electricity can be produced by merely disturbing the 

 power permanently secured in the ordinary magnet. 

 . It was thought that magnets would become weakened 

 by this constant disturbance of their magnetism ; but, 

 since its application to the purpose of manufacture, and 

 magneto-electricity has been employed in electro-plating, 

 it has been found that continued action for many 

 years, during which enormous quantities of electricity 

 have been thus given out and employed in producing 

 chemical decomposition, has not, in the slightest degree, 

 altered their powers. Thus a small bar of metal is 

 shown to be capable of pouring out, for any number of 

 years, the principle upon which the phenomena of mag- 

 netism depend. 



There are, however, differences, and striking ones, 

 between ordinary and magnetic electricity. In the 

 magnet we have a power at rest, and in the electrical 

 machine or galvanic battery, a power in motion. 

 Ordinary electricity is stopped in its passage by a plate 

 of glass, of resin, and many other substances ; but mag- 

 netism passes these with freedom, and influences mag- 

 netic bodies placed on the other side. It would appear, 

 though we cannot explain how, that magnetism is due 

 to some lateral influence of the electric currents. A 

 magnetic bar is placed over a copper wire, and it hangs 

 steadily in the direction of its length ; an electric current 

 is passed along it, and the magnet is at once driven to 

 place itself across the wire. Upon this experiment, in 

 the main, Ampere founds his theory of terrestrial mag- 

 netism. He supposes electrical currents to be travers- 

 ing our globe from east to west, and thus, that the 

 needle takes its direction, not from the terrestrial action 



