OF ARTS AND SCIENCES. 23 



We may conceive of this electric wind as a breeze of the ether: 

 the proof of the identity will be given later. 



It is in currents flowing along metallic wires that the phenomena 

 of electricity have been most carefully studied, and it is the phe- 

 nomena of such currents that have therefore been for the most part 

 utilized in electrical inventions. 



Nature's wind is used to waft our ships across the seas, and it is 

 perhaps not a wild idea to conceive of electric repulsion utilized to 

 support and propel heavily laden air ships through the space above 

 our heads; but it is with electric phenomena as they have been 

 investigated and utilized up to the present time that we have to 

 deal in this article, and this, as we have seen, means the phenom- 

 ena of electric currents flowing through metallic wires. 



What are some of these phenomena ? 



Electricity — or what we shall soon see is the same thing, a cur- 

 rent of ether — passes readily through a copper wire. To the ether 

 current, the wire is hollow; in electrical terms, it is a good con- 

 ductor. It also passes quite readily through an iron wire, but not 

 so readily as through copper. It passes still less readily through 

 a wire of carbon. It passes more readily through a large wire than 

 through a small wire. In all wires, there is more or less ethereal 

 friction or electric resistance. 



In virtue of this ethereal friction or electric resistance, the cur- 

 rent heats the wire through which it passes, — of course heating a 

 small wire more than a large one, and heating an iron wire more 

 than one of copper, and a carbon wire most of all. We see this in 

 our household system of electric lighting. The current passes 

 from the central station and throughout our houses to the lamps, 

 over comparatively large wires of copper, which it warms only 

 slightly; but coming to the lamps, it passes through a fine wire 

 of carbon, in which the friction and consequent heating is so great 

 that the filament becomes white hot; and were it not contained in 

 a glass globe, from which the air has been removed, it would take 

 fire and disappear. 



Again, an electric current flowing in a wire coiled around a bar 

 of iron converts the bar of iron into a magnet, so that it may at- 

 tract an iron armature placed near its end, and thus do mechanical 

 work. The converse of this is equally true, and if we move an 

 iron armature to or from the end of an iron bar around which a 

 wire is coiled, an electric current will be set up in the same coil, 

 and by means of the connecting wires may be carried to a distance 



