ELECTRICITY. 73 



energy of coal used in the mechanical working of a dynamo. All methods of 

 generating electricity bring about a disturbance of the electrical equilibrium 

 existing under normal conditions in ail matter. Whenever this equilibrium is 

 disturbed there is a tendency to re-establish it, and it is during the process of 

 re-establishing the equilibrium that work is done electrically. 



One of the principal reasons that electrical phenomena offered great diffi- 

 culties to the investigator is that the electric undulations taking place in the 

 ether produce no effect whatever on our senses. Waves of air in striking certain 

 nerves in the ear produce the sensation of sound ; waves of ether affect certain 

 other nerves in such a manner as to produce the sensations of heat and light, 

 but man has no nerves that are affected by electric or magnetic waves i. e., 

 he is magnetically and electrically blind and deaf. The slow development of the 

 science of electricity was due to this fact. 



Magnetism. The native iron ore known as lodestone or mag- 

 netite (ferrous ferric oxide) has the power of attracting bits of steel 

 or iron, and also possesses the property of pointing north and south 

 when suspended by a thread. Pieces of iron may be caused to 

 acquire the same properties, and all bodies possessing them are called 

 magnets, while magnetism is the term used to designate the magnetic 

 condition of matter. 



Any bar of steel or iron may be magnetized by drawing over it 

 lengthwise a magnet ; but while a piece of hard steel will remain 

 a magnet almost indefinitely, soft iron loses its magnetism very 

 readily. A pivoted or suspended magnet always places itself in the 

 direction of the " magnetic meridian' 7 of the earth i.e., nearly 

 north and south. The end of the magnet pointing north is called 

 its north pole, the other its south pole. On bringing one pole of a 

 magnet near a suspended magnet it is found that with magnetism, as 

 with electricity, like poles repel and unlike poles attract each other. 

 There exists also magnetic induction, corresponding to induction by 

 electricity. This can be shown by placing a bar of iron near a 

 magnet, when it is found that the end of the bar nearest the north 

 pole is converted into a south pole, and vice versa. 





When a magnetized bar is dipped into iron filings, masses of the filings adhere 

 to the two extremities i. e., to the two poles while none are found at the 

 centre. When a magnetic bar is cut in halves at the non-magnetic centre, 

 two magnets are produced ; and this cutting into smaller lengths may be con- 

 tinned indefinitely, with the result that each length, and finally each particle, 

 possesses two poles and an intermediate neutral zone. This fact, as well as 

 other considerations, has led to the assumption that each molecule of iron is 

 a magnet in itself. In ordinary iron these little magnets are not arranged 

 systematically, while in magnetized iron all the north poles point in one direc- 

 tion, all the south poles in the opposite direction. Moreover, it is supposed 



