Electric Lighting. 99 



armature eool. The wire coils pass very close to the pole- 

 pieces of the field-magnets, the very excellent workmanship 

 shown in the construction of the machine enabling this to 

 be clone with safety. The commutator is so arranged as to 

 supply a current to excite the field magnets without passing 

 into the outside circuit, whilst it also cuts out all coils that 

 are not used in generating a current, thus reducing the 

 resistance of the machine. In other machines the same end 

 is obtained by using a separate machine to excite the field- 

 magnets of the generator; this, whilst keeping the field- 

 magnets in perfectly uniform condition, lowers the resistance 

 and increases the electro-motive force to a considerable 

 extent. The question, however, arises as to the advisability 

 of using machines of high tension. Looking at electric 

 lighting as a thoroughly practical means for illumination, it 

 appears certain that it will be necessary to maintain a con- 

 siderable number of lights on one circuit. I refer now to 

 arc lights. The difficulties I mention do not apply to the 

 same extent to the incandescent lamp. In the earlier dcays 

 of electric lighting, where instalations were used in certain 

 buildings only, lights fed from single machines were found 

 convenient, and unquestionably the most economical for 

 very powerful lights. When, however, the method of light- 

 ing from a central station and supplying a very great number 

 of lights distributed at various distances from the generator 

 had to be determined, it became evident that it would be 

 impossible to carry it out by the same system. The immense 

 number of conductors required would alone be sufficient to 

 condemn it, apart from the cost of attendance to the number 

 of machines that would be in use. Therefore, systems 

 capable of supporting a number of lights from one machine 

 rapidly gained public favour, and the system that could 

 support the greatest number of lamps in the same circuit 

 has commercially been the greatest success. But has this 

 advantage been gained in a right direction ? and if the 

 present system be adhered to, does it not amount to either 

 a limit to the number of lights to be used or the introduction 

 of machines which for safety to human life are hardly to be 

 desired. The original dynamo-machines constructed to 

 generate low tension currents are perfectly harmless, the 

 current may be conducted by imperfectly insulated con- 

 ductors, as in the instance of the Berlin electric railway, 

 where the iron rails laid on wooden sleepers are the only 

 conductors used, and they answer perfectly even in 



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