ELECTRIC LIGHTING, PROGRESS OF. 



271 



all portions of his entire electrical plant have at L. The large steam-dynamo, of the type 

 been designed from this point of view. The used at this station, and which is to be used in 



system is, in many respects, analogous to that 

 in use with gas. This latter illuminant is dis- 

 tributed from the works through large mains 

 and under low pressure, suitable for direct is- 

 suance from the burner. In Mr. Edison's sys- 

 tem the current is of low electro-motive force, 

 110 volts between the terminals of the machine, 

 and is distributed through large mains laid un- 

 der-ground. The lamps are arranged in what 

 is known as multiple arc, that is, on cross- wires 

 between the house conductors, which them- 

 selves form cross-wires to the mains. As the 

 current passing through each lamp depends 

 upon its resistance and the electro-motive force 

 of the current, when this latter is maintained 

 constant, each lamp draws its proper supply 

 without regard to any other on the circuit. 

 The generators at the central station are like- 

 wise arranged in multiple arc, one pole of each 

 machine being connected with the outgoing 

 and the other to the return main. The dispo- 

 sition of the machines, and the mode in which 

 the circuits are actually arranged in practice, is 

 shown in the diagram (Fig. 4). Each main 

 consists of an iron tube containing two half- 



round copper conductors imbedded in a resin- 

 ous insulator. A main of this kind is carried 

 around each city block, and each one connected 



all similar installations, is shown in Fig. 5. 

 The magnetic field is produced by twelve hori- 

 zontal electro-magnets, united at their farther 

 ends by a massive heel-plate, seen at the back 

 of the figure, and terminating in the heavy 

 pole-pieces seen in the front of the illustration. 

 The armature, which is a long cylinder, is com- 

 posed of a core of a great number of thin 

 sheet-iron disks, insulated from each other and 

 fitting over a central wooden cylinder. The 

 copper is in the form of straight bars instead 

 of wire, in order to make the resistance as 

 low as possible. These bars are united at al- 

 ternate ends to as many disks of copper, the 

 connection being such that the current passes 

 along one bar, across a disk at one end, along 

 the bar diametrically opposite the first, across 

 a disk at the other end, then along a bar next 

 to the first bar, and so on, the effect being the 

 same as would be obtained by a continuous 

 copper coil of low resistance. The diameter 

 of the complete armature is 28 inches, its 

 length 5 feet, and its weight over four tons. It 

 is driven at a speed of 350 revolutions per 

 minute. Its resistance is only -00049 ohm. 

 The field coils form a 

 shunt circuit to that of 

 the machine, and have a 

 resistance of 21 ohms. 

 The engine is a horizon- 

 tal Porter -Allen of 130 

 horse - power, nominal. 

 The entire machine, in- 

 cluding the bed - plate, 

 weighs over thirty tons. 

 It has a normal capacity 

 of 1,200 lamps of 16 can- 

 dles each, but can supply 

 1,600 when necessary. 

 There are at present six 

 of these enormous dyna- 

 mos in place at the cen- 

 tral station, but the com- 

 pleted installation will 

 comprise twelve of them. 

 The current used by 

 each lamp is measured 

 very simply by means of a 

 meter, which consists of 

 an electrolytic cell through which a small 

 fraction of the current passes. The cell con- 

 tains sulphate of copper, which is decom- 



with those of the adjacent blocks through the posed, and the copper deposited upon one of 



boxes B, as shown. The conductors in these 

 mains are of uniform size, but by means of the 

 auxiliary mains, termed feeders, shown in the 

 dotted lines, the conducting capacity is in- 

 creased to any desired extent throughout any 

 portion of the district. The system can by 

 this means be adapted to any increase of con- 



the electrodes, the amount so deposited being 

 an accurate measure of the current which has 

 gone through. A meter has been designed in 

 which the amount of copper deposited is indi- 

 cated on a dial, as the gas passing is registered 

 on a gas-meter, but the meter at present sup- 

 plied to consumers is without registering appa- 



sumers as occasion arises. The way in which ratus, the consumption being determined by 



the dynamos are arranged with regard to the the meter-inspector by direct weighing of the 



circuit is shown at G, and the mode in which electrode. This form of meter is shown in 



the lamps are connected with the mains shown Fig. 6. 



