April 13, 1893] 



NATURE 



571 



down, under the direction of the late Sir William Siemens, 

 from the Palais de I'lndustrie to the Place de la Concorde, 

 upon which a tramcar worked by an electric motor plied up and 

 down with great regularity and success during the period of the 

 Exhibition. Yet few of those who saw in this experiment the 

 possibilities of a great future for a new mode of traction would 

 have ventured to predict that within ten years' time, in the 

 United States alone, over 5,000 electric cars would be in opera- 

 tion, travelling 50,000,000 miles annually, and carrying 

 250,000,000 passengers, or that electrical traction would have 

 solved the problem of better communication in London and 

 other large cities. Two years before the exhil)ition in Paris the 

 late Dr. Werner Siemens had exhibited at the Berlin Exhibition 

 in 1879 an experimental electric tramway on a much smaller 

 scale, and his firm had put down in 188 1 the first permanent 

 electric railway in the short length of line at Lichterfelde, near 

 Berlin, which, I believe, is still at work. In the same year Dr. 

 William Siemens undertook to work the tramway, then pro- 

 jected, between Portrush and Bushmills, in the north of Ireland, 

 over six miles in length, by electric power, making use of the 

 water power of the Bush River for the purpose, an undertaking 

 which I had the advantage of carrying out under his direction. 

 It is no pan of my object to-night to follow further the history 

 of electric traction, which is so recent that it is familiar to 

 all ; but, in alluding to these initial stages of its development, 

 I have desired to recall that it was to the foresight and energy of 

 Dr. Werner and Dr. William Siemens, and their skill m apply- 

 ing scientific knowledge to the uses of dailv life, which gave 

 the first impulse to the development of the new elecirical power. 



The problem of electric traction may be naturally considered 

 under three heads : — 



(i) The produc'ion of the electrical power. 



(2) Its distribution along the line. 



(3) The reconversion ot electrical into mechanical power, in 

 the car motor or locomotive. 



The first of these here in England at any rate is dependent 

 upon the economical production of steam power, although there 

 are essential points of difference between the conditions under 

 which steam power is required for electric traction purposes and 

 for electric lighting. But in Scotland and Ireland and in many 

 countries abroad there is abundant water power, now only very 

 partially utilised. The Portrush line is worked in part by water 

 and in part by steam power, but in the Bessbrook and Newry 

 Tramway (of which there is a working model on the table) 

 water power is exclusively used. 



A few experiments will show that the demand for power on 

 the generating plant is greatest at the moment of starting 

 the car or tram, when in addition to the power required to over- 

 come the frictional resi>tances pjwer is also required to accelerate 

 the velocity. Thus, if instead of a single car there are a number 

 of trains moving on the one system, and it so happens that 

 several are starting together, the demand made upon the gener- 

 ating plant may at one moment be three or four limes as great 

 as that made a few seconds after. This is shown in the diagrams 

 which exhibit the variation of current supplied by the generators 

 on the City and South London Railway, with eight trains run 

 ning together, the readings being taken every ten seconds. The 

 maxima rise as high as double the mean; thus the generating 

 plant must be capable of instantly responding to a demand 

 double or even treble the average demand upon it. 



In electric lighting it is true there is not less variation between 

 the maximum demand and the mean taken during the ordinary 

 hours of lighting, but it is only in the event of sudden fog that 

 the probable demand cannot be accurately gauged beforehand, 

 and provided for by throwing more generators into action. Thus 

 in a lighting station each generator may be kept working 

 approximately at its full load, and therefore under conditions of 

 maximum economy, whereas in a traction station the whole 

 plant must be kept ready to instantaneously respond to the 

 maximum demands which maybe made upon it, and must there- 

 fore necessarily work with a low load factor, and consequently 

 with diminished economy. So important is the influence on 

 cost of production of the possible demand in relation to average 

 demand, that the Corporation of Manchester under their 

 order for electric supply, have decided upon the advice of 

 their engineer to annually charge a customer £,'>, per quarter 

 for each unit per hour of maximum supply which he may 

 require, in addition to 2d. per unit for each unit actually 

 consumed, i.e. for being ready to supply him with a certain 

 amount of electrical power if required to do so, they charge an 



^'O. 1224, VOL. 47] 



additional sum equivalent to the chaise for its actual consump- 

 tion for 1440 hours. 



In one respect water power has an economic advantage over 

 steam power, because although steam engine and turbine alike 

 work with greatly reduced efficiency at reduced loads, when 

 the turbine gates are partially closed and the water restrained in 

 the reservoir, it is not subject to loss of potential energy, 

 whereas the energy of the steam held back by the valves of the 

 engine suffers loss through radiation and condensation. 



At Bessbrook the turbine and generator dynamo combined 

 yield 60 per cent, of the energy of the water as electrical energy 

 available for work on the line, but when the load is reduced to 

 a third of the full load the efficiency is reduced to 33 per cent. 

 So on the City and South London line a generator engine and 

 dynamo will yield, when working at their full load, 78 per cent, 

 of the indicated horse-power as useful electrical power, but at 

 half load the efficiency falls to 65 per cent. Notwithstanding 

 these conditions the generator station of the City and South 

 London line is producing electrical energy at a cost of i •5611'. per 

 Board of Trade unit, which is less than the annual average cost 

 of production of any electric station in England, with the single 

 exception of Bradford, which has the advantage both of cheap 

 coal and cheap labour. In output it is the largest of any Electric 

 Generating Station in England, the total electrical energy 

 delivered in 1892 being 1,250,000 Board of Trade units, the 

 second on the list being the St. James and Pall Mall wi h 

 1,186,826 units. 



Let us pass now to the consideration of the distribution of the 

 electric power along the line. I have equipped the three model 

 tracks before you with three different kinds of conductors. In 

 two of them the rails of the permanent way, which are 

 necessarily uninsulated, are made use of for the return current. 

 This plan, with I believe the almost .-ingle exception of the 

 Buda Pesth Tramway, has been universally adopted with the 

 object of saving the cost of a return conductor ; but it is doubt- 

 ful whether such an arrangement can be considered final, for it 

 must necessarily create differences of potential in the earth, which 

 already in some instances have had disturbing effects upon our 

 observatories, or upon our telegraph and telephone systems. It 

 appears to be probable in the more or less distant future that the 

 use of the earth for the passage of large current will be guarded 

 by legislation ; and that it will be reserved for the more delicate 

 and widely extended operations of telegraphy and telephony. 

 These disturbances may of course be easily avoided by the use 

 of an insulated conductor for the return circuit. In the case of 

 conductors which are in such a position that contact may be 

 made from them to the ground through the body of a horse or 

 some other animal coming into contact with them, there is 

 another strong argument for an insulated return, as many 

 animals, and notably horses, are far more sensitive to electric 

 shock than man. It is not perhaps well known, but still a fact, 

 that a shock of 250 volts is quite sufficient to kill a horse almost 

 instantaneously. 



The first model has a single overhead conductor with return 

 by the rails ; but in place of a single fishing-rod collector or 

 trolley to take the current from the overhead wire there are fixed 

 on the car two rigid bars, one at each end. which slide along 

 the under surface of the wire and make a rubbing contact against 

 it. This system, devised by Dr. John Hopkinson, has the 

 advantage that there is less difficulty in main'aining contact on 

 uneven roads or on curves, and that the catenaries of the sus- 

 pended wire may be hung with greater dip, and therefore with 

 less tension. Again, the double contact obviates the frequent 

 breaks and consequent sparking of a single trolley system. The 

 second model >hows the system adopted on the City and South 

 London line, and more recently followed on the Liverpool Over- 

 head line, of a conductor of channel steel, upon which collectors 

 fixed to the locomotives make a sliding cont.act. The third 

 track shows an overhead system like the first, but with an insu- 

 lated return in place of return by the rails. 



The characteristic feature of an electric motor is that it de- 

 livers us the mechanical power we require directly in the form 

 of a couple about an axis instead of in the form of a rectilinear 

 force, as is the case with steam, gas, or air engines, which 

 must be reduced to a rotary form by connectintj rod and crank. 

 Thus it is possible to sweep away all intermediate gear, and to 

 arrive at once at the simplest of all forms of a traction motor, 

 consisting of but one pair of wheels fixed on a single axle with 

 the armature constructed directly upon it, with its magnets sus- 

 pended from it arid maintained in their position against the 



