THS 



VOLUME 



ORGAN IZ 

 KNOWLEDGE 



STORY 

 AND' PICTURE 



FOUR 



ELECTROLYTE, elek'trolite, any chemical 

 compound which can be decomposed by an 

 electric current. The substance resulting from 

 such decomposition is called an ion. 



ELEC'TROMAG'NET, a magnet produced 

 by the magnetic action of an electric current. 

 An electromagnet consists essentially of a coil 

 of wire having an iron core, and it is usually of 

 horseshoe form. The story of the development 

 of the electromagnet is the story of our modern 

 electrical industries, for the electromagnet is 

 the foundation of nearly all the great electrical 

 inventions. Without it there could be no tele- 

 graph, telephone, electric light or electric power. 



Strong electromagnets are used for lifting 

 heavy weights of iron. The lifting magnet is 

 lowered from the arm of a crane until it is in 

 contact with the iron; the electric circuit is 

 then closed and the magnet attracts the iron 

 and holds it firmly. Magnet and iron are then 

 lifted by the crane, swung to the place where 

 it is desired to deposit the iron, when the 

 current is cut off and the magnet releases its 

 hold. In this way masses of iron weighing 

 many thousands of pounds, as well as .red-hot 

 iron, can readily be moved. 



The strength of an electromagnet depends 

 on the number of turns of wire, the strength 

 of the current and the permeability of the iron 

 core. By the permeability of the iron core is 

 meant the magnetic strength produced in the 

 iron by a certain magnetizing force; the 

 greater the permeability the more strongly 

 will a given current magnetize the iron. The 

 invention of an insulating covering made it 

 possiDle to wind many turns of wire on an 

 iron core and produce a strong electromagnet 

 (see INSULATOR). This in turn made possible 

 the telegraph relay, in which a very weak cur- 

 rent produces sufficient magnetic force to move 

 the armature. It also made possible the strong 

 electromagnets used in modern dynamo- 

 electric machinery. E.E.B. 



ELEC'TROMAGNET'IC THEORY OF 

 LIGHT. According to this theory light con- 

 sists of very short electromagnetic waves, com- 



monly called electric waves, which are trans- 

 mitted through the ether (see ELECTRICITY). 

 The wireless telegraph message is also trans- 

 mitted by waves in the ether. The two kinds 

 of waves are known to be alike in many re- 

 spects; either may be reflected from a mirror 

 surface of metal; electric waves are bent on 

 entering certain substances as light is bent on 

 entering water; certain substances are trans- 

 parent to electric waves as glass is transparent 

 to light. The fact that light waves and elec- 

 tric waves are alike in so many respects leads 

 to the belief that they are of the same kind, 

 the only difference being in the length of the 

 waves. It was Maxwell's mathematical proof 

 that electromagnetic energy is transmitted by 

 waves of the same kind as light waves, which 

 led to the discovery of the wireless telegraph. 



The waves used in wireless telegraphy are 

 produced by a violent electrical discharge in 

 the air. The discharge at the spark gap of a 

 wireless telegraph sending instrument consists, 

 according to the electron theory, of violent 

 motion of electrons across the gap. Light is 

 believed to be produced also by motion of the 

 electrons. To produce light the electrons must 

 vibrate in a very small space with very great 

 speed. The space in which the electron vi- 

 brates is equal to that occupied by an atom. 

 The speed is so great that the electron to pro- 

 duce light that is just visible (red light) must 

 make about as many vibrations in a second as 

 there are seconds in twelve million years. We 

 know this because we know the number of light 

 waves produced in one second and it requires 

 one vibration for each wave. To produce 

 white light the electron must vibrate much 

 faster. Heating an object sets the electrons 

 vibrating violently and thus causes them to 

 send out very short electromagnetic, or light, 

 waves. In this manner heat produces light. 



Thus the electromagnetic theory of light and 

 the electron theory of electricity fit together 

 as parts of one theory and explain better than 

 any other theory the known facts of electricity 

 and light. E.E.B. 



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2001 



