362 ACTION OF ELECTEIC CURRENTS. [SECT, xxxii. 



through them. All the experiments that can be performed 

 with the cylinder might be accomplished with a magnet. 

 That end of the cylinder, in which the current of positive 

 electricity is moving in a direction similar to the motion of 

 the hands of a watch, acts as the south pole of a magnet, 

 and the other end, in which the current is flowing in a con- 

 trary 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 common 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 ordinary electricity can be 

 accumulated in insulated 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 an- 

 other, 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 what- 

 ever when its motion is discontinuous or interrupted, like the 

 current produced by the common electrical machine when a 



