ELECTRIC LIGHTING, PROGRESS OF. 



305 



sating conductors may therefore be quite small 

 and inexpensive. This method of distribution 

 is applicable to cases in which but one gener- 

 ator is used, the compensating conductor then 

 being connected to an extra brush on the ma- 

 chine placed between the two other brushes, 

 as shown in Fig. 3. This method of distribu- 



Fre. 3. 



tion has not as yet been put into use, but Mr. 

 Edison designs to employ it in the next electric- 

 light district which is soon to be established in 

 New York. The great importance of this sys- 

 tem of distribution will be appreciated when 

 it is remembered that even with the high-re- 

 sistance lamps used by Mr. Edison the cost of 

 the street mains is equal to the entire generat- 

 ing plant, and that tha great outlay necessary 

 for plant is to-day the chief obstacle to fur- 

 nishing the electric light cheaply. 



The system of distribution, which consists 

 in placing the lamps or other apparatus to be 

 used in the secondary circuit of an induction- 

 coil, the primary coil of which is in the main 

 circuit, has been proposed by various inventors 

 in the past few years. Mr. Edison himself 

 took out some patents on this method of dis- 

 tribution, though he has never put it into 

 practical use. M. Jablochkoff, in 1877, used 

 this system with his candles, employing for 

 this purpose an alternating-current generator. 

 VOL. xxin. 20 A 



The late J. B. Fuller also proposed to use the 

 system in 1879. His induction-coils were made 

 by winding over an iron core coils of coarse 

 wire at each end and a fine- wire coil at the 

 middle, the former being included in the main 

 circuit, and the latter forming the local circuit 

 in which the lamps were placed. Any number 

 of such induction apparatus or groups of them 

 may be placed on a circuit in series which the 

 tension of the current will permit, and by con- 

 necting the fine- wire coils in series or in multi- 

 ple the intensity or the tension of the lamp-cur- 

 rent may be varied within wide limits. The 

 death of Mr. Fuller cut short his experiments 

 in this direction, so that his apparatus was 

 never made practical use of. The secondary 

 current was also employed by Professors 

 Thomson and Houston for operating their vi- 

 bratory arc-lamp. For this purpose each lamp 

 was placed in a separate secondary circuit, and 

 by means of an electro-magnet, one of the car- 

 bon electrodes, usually the negative, was given 

 a rapid vibratory motion to and from the upper 

 positive carbon. This form of lamp was, how- 

 ever, abandoned by them, and they subse- 

 quently resorted to an arc-lamp operated in 

 the ordinary manner by a continuous current. 

 Various other inventors have patented differ- 

 ent forms of induction apparatus, but none of 

 them have passed into actual use. Quite re- 

 cently, however, this method has been revived 

 in England by Messrs. Goulard and Gibbs, who 

 have put the system into operation along the 

 line of the London Metropolitan railway (un- 

 derground). 



They construct their induction - coils by 

 forming each circuit primary and secondary 

 of cables containing a number of wires, and 

 then winding these cables as the wire is 

 ordinarily wound on such apparatus that is, 

 the coarse wire on a central paper or other 

 insulating tube, and the secondary over this. 

 The iron core is composed of a bundle of 

 wires, and is contained within a brass cylinder, 

 by the withdrawal of which the strength of 

 the secondary current can be regulated, and 

 consequently that of the lights. The primary 

 coil is in the main circuit, through which is 

 sent an alternating current from an alternat- 

 ing-current dynamo. This current is of high 

 tension, but, as this circuit is a permanently 

 closed metallic one, there is no danger from 

 the system on the score of the tension of the 

 main circuit current. 



Messrs. Goulard and Gibbs combine a num- 

 ber of their induction-coils into one apparatus 

 of sufficient capacity to do the lighting re- 

 quired say, that of a private house and con- 

 nect the coils so that any desired combination 

 of them, in series or multiple, may be made. 

 The secondary currents can therefore be made 

 to give currents of high tension suitable for 

 a number of arc-lamps in series, or low tension 

 such as are required for incandescent lamps in 

 multiple. In the installation on the Metro- 

 politan railway five stations are lighted, . each 



