Page:Collier's New Encyclopedia v. 09.djvu/527

LEFT TBANSMISSION 465 TRANSPORTATION found profitable to transmit electric power is 220 miles. The plants at Niagara now generate upward of 250,000 horse power, and when equipment now in course of construction is complete the figure will be raised to 500,000 horse power. The greatest distance supplied is from Niagara to Syracuse, a distance of 165 miles. Plants in California supply power over a still greater distance, reach- ing in one case the high figure of 220 miles. Some of the details of the transmission equipment may now be briefly described. A device of some importance is the Lightning Arrestee: This is used to pro- tect the system against lightning dis- charges and other abnormally high volt- ages. The aluminum arrester is com- monly used, which consists of a nest of aluminum cones immersed in an electro- lyte, the cones being covered with a film of hydroxide. At a low voltage, only a very low current can flow through this contrivance, but when the voltage rises the possible current that it can carry is very high. As soon as the voltage drops below a certain critical point, the high resistance is restored and the cur- rent falls correspondingly. The arrester acts, so to speak, as a safety valve, re- leasing high voltages just as the safety valve on a steam line will release high steam pressure. The actual service line itself is protected from lightning by run- ning a steel wire parallel to the upper wires, this steel wire being grounded at every support. The lightning passes to the ground through this wire, rather than through the copper wires and glass or porcelain insulators. Switches are an- other important detail in high voltage systems. Oil switches are most common- ly used, in which the contacts are im- mersed in insulating oil, thus preventing the formation of an arc when a current is broken. They are generally operated at a distance by a system of levers, or by means of a small motor, and impor- tant switches are frequently arranged with each pole In a separate chamber of brick or concrete. On the switchboard are assembled ammeters, voltmeters, wattmeters, rheostats, and all the levers for controlling the generating and trans- mitting system, so that the man in charge can tell almost at a glance the condition of any part of the circuit. In cases where the area of distribution is small, direct instead of alternating current is used. In order to take care of variation in pressure in the supply line, caused by fluctuation in consump- tion, a storage battery is connected in parallel with the dynamo. When con- sumption is small, excess current from the dynamo flows to the batteries and charges them. When consumption is high, current from the dynamo is sup- plemented with that from the batteries. TRANSMISSION OF POWER, the doing of useful work at a distance from the engine or whatever other source sup- plies the energy. The revolving shaft of a screw steamer transmits rotary mo- tion through a considerable distance; but for long distance transmission ordinary mechanical devices, if they do not alto- gether fail, lose greatly in efficiency. Cable cars also form a good illustration. It is in electricity, however, that we find the most promising agent for indefinite transmission of power. Thus a dynamo- electric machine may be worked by a waterfall; its voltage or potential may be transmitted along wires to distant stations, and there transformed into cur- rents capable of driving an electric motor and keeping a whole factory in operation. Over 60,000 hoi'se power of electric current generated by Niagara Falls is in use in the many factories established at Niagara Falls and in Buffalo, N. Y., 26 miles away. In the latter city street railways, grain elevators and manufac- turing plants are run by this current, which is brought to the outskirts of the city over bare copper wires, and then distributed through the city in under- ground conduits. TRANSPORT, a ship or vessel em- ployed by a government for carrying soldiers, warlike stores, or provisions from one place to another. At the begin- ning of the American-Spanish War the United States had no ships of this class. A number of coastwise crafts were pur- chased and hastily transformed into transports, on which troops were shipped to Manila and other points. Although so hastily fitted up, they proved ade- quate. When the war closed, the United States Government fitted up a number of these vessels as model transports. They have every convenience and comfort, in- cluding gymnasiums, bath-rooms, hospi- tals and electric lights, etc. When the United States entered the World War in 1917 all the transports were in use as ocean freighters, but by remodeling the seized German ships and by borrowing transports from England the millions of American soldiers were carried across the sea with a minimum loss of life. TRANSPORTATION, a punishment till recent times in general practice in Great Britain for crimes of the more serious description, but falling short of the penalty of death. It varied in dura- tion from seven years to the termination