SECT. XXXI. ELECTRIC CURRENTS. 317 



as the south pole of a magnet, and the other end, in which the 

 current is flowing in a contrary direction, exhibits northern 

 polarity. 



The phenomena mark a very decided difference between the 

 action of electricity in motion or at rest, that is, between Voltaic 

 and static electricity ; the laws they follow are in many respects 

 of an entirely different nature, though the electricities themselves 

 are identical. Since Voltaic electricity flows perpetually, it 

 cannot be accumulated, and consequently has no tension, or 

 tendency to escape from the wires which conduct it. Nor do 

 these wires either attract or repel light bodies in their vicinity, 

 whereas static or ordinary electricity can be accumulated in insu- 

 lated bodies to a great degree, and in that state of rest the 

 tendency to escape is proportional to the quantity accumulated 

 and the resistance it meets with. In ordinary electricity, the 

 law of action is, that dissimilar electricities attract and similar 

 electricities repel one another. In Voltaic electricity, on the 

 contrary, similar currents, or such as are moving in the same 

 direction, attract one another, while a mutual repulsion is exerted 

 between dissimilar currents, or such as flow in opposite directions. 

 Common electricity escapes when the pressure of the atmosphere 

 is removed, but the electro-dynamical effects are the same whether 

 the conductors be in air or in vacuo. 



The effects produced by a current of electricity depend upon 

 the celerity of its motion through a conducting wire. Yet we 

 are ignorant whether the motion be uniform or varied, but the 

 method of transmission has a marked influence on the results ; 

 for, when it flows without intermission, it occasions a deviation 

 in the magnetic needle, but it has no effect whatever when its 

 motion is discontinuous or interrupted, like the current produced 

 by the common electrical machine when a communication is 

 made between the positive and negative conductors. 



M. Ampere has established a theory of electro-magnetism 

 suggested by the analogy between electro-dynamic cylinders and 

 magnets, founded upon the reciprocal attraction of electro-cur- 

 rents, to which he reduces all the phenomena of magnetism and 

 electro -magnetism, by assuming that the magnetic properties 

 which bodies possess derive these properties from currents of 

 electricity, circulating about every part in one uniform direction. 

 Although every particle of a magnet possesses like properties 



