October i, 1891 



NATURE 



523 



potential difference at the dynamo terminals being some 

 1850 volts. 



The arrangement of the machines was very bitterly 

 criticized : some pronounced the result a great success ; 

 others that the whole thing was a fraud, that the power 

 did not go from the dynamo at Paris to Bourget and back 

 again, but that, owing to leakage from one of the tele- 

 graph lines to the other, the actual distance over which 

 the power was transmitted was far less than the distance 

 stated. 



The next experiments were made with the same 

 machines rewound and improved in insulation. They 

 were now employed to transmit power over 8| miles, from 

 \'izille to Grenoble, a pair of siliiiuni bronze wires 0079 

 inch in diameter being used to connect the dynamo and 

 motor. A difference of potential of about 3000 volts was 

 employed, and 7 horse-power was given off by the motor 

 with a commercial efficiency of 62 per cent. 



This experiment of transmitting power from Vizille to 

 Grenoble in 1883 was distinctly successful, and constituted 

 a great advance on anything in electric transmission that 

 had been attempted before. It is interesting, for example, 

 to compare it with the transmission from Hirschau to 

 Munich by Mr. Schuckertin 1882, and which was regarded 

 as very striking at the time it was carried out. 



Transmission of Power. 



1882. _ , . 1883. 



Hirschau to Munich. Vizille to Grenoble. 

 Distance in miles ... 3^ .. 8| 



Diameter of conducting 



wire in inches ... 018 ... 0*079 



Horse-power delivered 



by electromotor ... 5"8 ... 7 



Commercial efficiency 



of the transmission .. 36 ... 62 



Potential difference at 



terminals of dynamo 



in volts ... .. 700 ... 3000 



Comparing, then, the Vizille transmission of 1883 with 

 the Hirschau transmission of 1882, we see that the dis- 

 tance was twice as great, the cross-section of the wire 

 less than one-quarter, the power somewhat greater, and 

 the efficiency nearly twice as great ; this great improve- 

 ment being effected by using a pressure of 3000 instead 

 of 700 volts. 



But with 3000 volts the limit of constructing the com- 

 mutator of an ordinary direct current dynamo or motor 

 is reached — a fact which was not appreciated by M. 

 Deprez. For when it was decided somewhat later to try 

 and transmit 200 horse-power through 35 miles of copper 

 wire o'2 inch in diameter, stretched on telegraph poles 

 between Creil and Paris, by using a pressure of 6000 or 

 more volts, the same system of direct current dynamo 

 and motor, that had been employed by M. Deprez in his 

 previous transmissions, was resorted to The result was 

 that the 200 horse-power had to be reduced to 100, and 

 the dynamo and motor were burnt up time after time. 



Eventually, after the expenditure of a very large sum 

 of money, spent in several rewindings of the machines, 

 &c., M. Deprez succeeded in 1886 in obtaining from the 

 shaft of the motor at Paris 52 horse power, this being 45 

 per cent, of the power spent in driving the dynaino at 

 Creil. The power delivered at Paris was distributed by 

 coupling a low potential difference dynamo to this motor, 

 and using the current developed by this dynamo for 

 driving various smaller motors, so that the power actually 

 delivered to the pumps, &c., was soinewhat less than the 

 52 horse stated above. 



In the use of a dynamo and motor each with a high 

 resistance armature and a low resistance field magnet, the 

 fields being produced by separate excitation, and in the 

 employment of a motor-dynamo for utilizing the received 

 power, M. Deprez expressed his approval of the very 



NO. I 144, VOL. 44] 



plan proposed by Profs. Ayrton and Perry in 1879 for 

 " sending by even quite a fine wire a small current," and 

 so obtaining " an economic arrangement for the trans- 

 mission of power." 



This experiment, although very costly, had consider- 

 able interest, in showing that as much as 52 horse-power 

 could be actually delivered at the end of thirty-five miles of 

 copper wire 02 inch thick, and that a pressure of 6000 

 volts could be practically employed with a lead covered 

 insulated conductor. But probably the most important 

 lesson learned from it was, that when the distance 

 over which power had to be transmitted was so great that 

 a pressure of 6000 volts became necessary to obtain 

 economy in the conducting wire, an alternating and not a 

 direct current ought to be used. 



While these various experiments of M. Deprez with 

 direct currents were being carried out, the transmission 

 of power by means of alternating currents had been pro- 

 gressing in the face of considerable opposition. The 

 exhibition at the Aquarium, Westminster, in the spring of 

 1883, will probably be chiefly remembered from its being 

 there that Messrs. Gaulard and Gibbs showed what they 

 called a " secondary generator," which was simply an im- 

 proved form of Ruhmkorff induction coil, without the 

 ordinary vibrating make and break. A current from an 

 alternating dynamo was sent round one of the coils, and 

 to the terminals of the other were attached lamps, the 

 brightness of which could be varied by pulling out the 

 iron core of the induction coil more or less, as is done 

 with medical coils to alter the strength of the shocking 

 current. 



Nobody thought much of the " secondary generator '' ; 

 it seemed to have no very special use ; the iron core felt 

 very hot, so that there would be a new waste of power 

 introduced into electric lighting by the use of secondary 

 generators. Besides, the electricians saw that Messrs. 

 Gaulard and Gibbs were employing methods and ap- 

 paratus for measuring the power which must give totally 

 erroneous results when used with alternating currents ; 

 and so, forgetful of the fact that invention is frequently 

 quite ignorant of the language of the text-book, they 

 decided that there was nothing in it. 



But Messrs. Gaulard and Gibbs believed in their 

 secondary generator, whatever electricians and the 

 technical press might say ; they put them at the 

 Notting Hill Gate, Edgware Road, Gower Street, King's 

 Cross, and Aldgate stations of the Metropolitan Railway, 

 joined the fine wire coils of all the generators in series 

 with one another, and sent a small alternating current 

 through the whole circuit from a dynamo placed at 

 Edgware Road. Lamps of different kinds attached to 

 the thick wire coils of each of the generators at the five 

 railway stations burned steadily and brightly ; an alter- 

 nate current motor, even, which was put at one of the 

 stations, revolved rapidly : but what a great waste of power 

 there must be in all this unnecessary transformation, said 

 the learned. 



Well, in the spring of the next year, 1884, Dr. J. Hop- 

 kinson te-.ted the efficiency of these secondary generators 

 on the Metropolitan Railway, and, to the surprise of 

 nearly everyone, it came out close on 90 per cent. 



In the autumn of the same year, in connection with 

 the Exhibition at Turin, power was transmitted to Lanzo, 

 twenty-five miles away, by means of a bare overhead wire 

 rather less than one-quarter of an inch in thickness, and, 

 by means of Gaulard and Gibbs's secondary generators, 

 the power was distributed at Lanzo and elsewhere along 

 the route, for lighting incandescent and arc lamps. The 

 jury reported that the efficiency of the transformers was 89 

 per cent., the whole distribution strikingly successful, and 

 a prize of 10,000 francs was awarded to Messrs. Gaulard 

 and Gibbs by the Italian Government. 



No electromotors, however, appear to have been 

 driven by the transmitted power, for, even in 1884, alter- 



