304 



ELECTRIC LIGHTING, PROGRESS OF. 



the theoretical maximum points the points 

 joined by a line at right angles to the line 

 drawn through the center of the field-mag- 

 net poles are in practice given a lead, or 

 displaced in the direction of rotation. Ac- 

 cording to Mr. Westou, the reason of this is 

 that the field-magnets tend to induce magnetic 

 poles in the iron core of the armature in the 

 line joining their poles, while the rotating coil 

 of wire wound on the core tends to induce 

 poles in this core at points at right angles to 

 this. The real maximum points are, therefore, 

 on a line between the theoretical ones and 

 that joining the field-magnet poles. The posi- 

 tion of these points changes with every varia- 

 tion of the strength of the field-magnets due to 

 variations in the current flowing in the field- 

 coils, while the position of the brushes remains 

 unchanged. That the difference of potential 

 between these should remain constant, it is 

 necessary that the position of the maximum 

 points should not change, and this will be the 

 case when the actual and theoretical positions 

 coincide. 



To realize this it is only necessary to make 

 the magnetic effect of the field upon the arma- 

 ture-core so greatly preponderate over that of 

 the wire upon it that the effect of this latter 

 is inappreciable. This he accomplishes by mak- 

 ing his field-magnets of great strength, wind- 

 ing but a single layer of wire upon the arma- 

 ture-core, and making this core, which con- 

 sists of a number of sheet-iron disks, with pro- 

 jections which come close to the face of the 

 magnet - poles. With this construction Mr. 

 Weston states that the theoretical and actual 

 maximum points so completely coincide that 

 the machine can be run in either direction 

 without changing the position of the brushes. 

 The dynamo is shunt-wound that is, the field- 

 magnets are placed in a shunt to the main cir- 

 cuit. 



Mr. Edison has continued to improve the de- 

 tails of his system, his latest improvement be- 

 ing an important modification of his system of 

 distribution by means of which the cost of the 

 conductors is materially reduced. Heretofore 

 he has used the simple multiple-arc system. 

 In this system each lamp requires its own sup- 

 ply of current, so that, to maintain a hundred 

 lamps, one hundred times the amount of cur- 

 rent must be transmitted as to maintain one. 

 If, however, the lamps be arranged on a mul- 

 tiple-series system that is, a system in which 

 each cross-circuit contains two or more lamps 

 arranged in series the supply of current will 

 depend upon the number of series circuits and 

 not upon the individual lamps. Thus, if two 

 lamps be placed in series, only one half the 

 current will need to be transmitted which 

 would be required in the simple series. If 

 three lamps are placed in series, only one 

 third the current will be required, and so on. 

 The electro-motive force of the current must, 

 however, be proportionately increased. The 

 defect of this arrangement is that the lamps 



are no longer independent of each other: 

 whenever one of a series is turned out, all of 

 that series must be. If they were not, they 

 would be destroyed by the increased current 

 which would flow through them on account of 

 the diminished resistance of the cross-circuit 

 in which they are placed. 



Mr. Edison has, however, succeeded in de- 

 vising a way of rendering the lamps in a mul- 

 tiple-series circuit independent of each other, 

 and thus rendering it as practicable for a gen- 

 eral distribution as the simple series. How he 

 accomplishes this is shown in Fig. 2, which 

 represents three lamps arranged in series on 



FIG. 2. 



each cross-circuit. The dynamos A, A, A, 

 are connected together in series, that is, one 

 after another. The two main conductors, P 

 and N, are connected, the one to the positive 

 pole of the first machine and the other to the 

 negative pole of the last. Between each line 

 of lamps compensating conductors, as Mr. Edi- 

 son terms them, are run to the generators and 

 connected with the conductor joining them, as 

 shown. With this condition of things, when 

 the same number of lamps are in each circuit, 

 no current will flow through the compensat- 

 ing conductors, but will pass from the main 

 positive conductor through each cross-circuit. 

 When, however, the number of lamps is un- 

 equal in two adjacent circuits, the excess of 

 current above that necessary for the smaller 

 number of lamps will flow through the com- 

 pensating conductor between them. In prac- 

 tice, the circuits would be so arranged that 

 the number of lamps in adjacent ones would 

 be nearly the same all the time. The compen- 



