Fan. 11, 1883] 
NATURE 
255 
power has turned the attention of engineers to the consideration, 
whether electricity could not successfully supplant steam for the 
propulsion of trains and tram-cars; whether it could not, in fact, 
supply an efficient means of transmitting power, the absence of 
which caused Stephenson to abandon ropes in favour of a heavy 
locomotive engine. 
The whole question, like every similar one, is mainly a ques- 
tion of expense; and what we have to consider is, whether 
electric transmission on the whole leads to greater economy than 
can possibly be obtained by the employment of any kind of 
locomotive. The average weight of a locomotive is about that 
of six carriages fullof people ; ten carriages compose an ordinary 
train, hence the presence of the mass of the locomotive adds at 
least 50 per cent. to the horse-power absolutely necessary to 
propel the carriages alone, and therefore at least 50 per cent to 
the amount of coal burned. But there is another most serious 
objection to the engines, perhaps even more important than the 
preceding. The heavy engine passing over every part of the 
line necessitates the whole line and all the bridges being made 
many times as strong, and therefore many times as costly, and 
the expense of maintenance consequently also far greater, than 
if there were no locomotive. And it is not possible to make the 
enyine much lighter ; for it would not have then sufficient ad- 
hesion with the rails to be able to draw the train; in fact, you 
cannot diminish the weight as long as the train is propelled with 
only one or two pair of driving wheels as at present. The em- 
ployment of electricity, however, will enable a train to be driven 
with every pair of wheels, just as the employment of compressed 
air enables every pair of wheels to brake the train. 
To propel a train, we must either utilise the energy of coal 
by burning it, or use the energy possessed by a mountain 
stream, or the energy stored up in chemicals, and which is given 
out when the chemicals are allowed to combine, or we must 
employ the energy of the wind. Practically we employ at 
present only the first store for propelling railway trains—the 
potential energy of coal; and that is to a great extent the store 
on which we shall still draw, even when we employ electric 
railways. For experience shows that, with the modern steam- 
engine and dynamo, at least one-twentieth of the energy in coal 
can be converted into electric energy ; and that this is at least 
twenty times as economical as the direct conversion of the 
energy of zinc into electric energy by burning it in a galvanic 
battery. 
But it may be asked, did not Faraday’s discovery, in 1831, 
that a current could be produced by the relative motion of a 
magnet and a coil of wire, settle this point half a century ago? 
Theoretically—yes ; practically, however, the problem was very 
far from being solved, because the dynamo machine was very 
unsatisfactory, and it was not until Pacinotti, in 1860, suggested 
the solution of the problem of obtaining a practically continuous 
current from a number of intermittent currents, and until 
Gramme, about 1870, carried out Pacinotti’s suggestion in the 
actual construction of large working machines, that the me- 
chanical production of currents became commercially possible. 
[Experiments were then shown illustrating the complete electric 
tran-mission of power, a gas-engine on the platform giving 
rapid motion to a magneto-clectric machine, and the current 
thereby produced sent through an electro-motor at the other end 
of the room, which worked an ordinary lathe. ] 
In electric transmission of power there is not only waste of 
power from mechanical friction, but also from electric friction 
arising from the electric current heating the wire, through which 
it passes. 
It was then explained and demonstrated experimentally that 
this latter waste could be made extremely small by placing so 
light a load on the electro-motor, that it ran nearly as fast as the 
generator or dynamo, which converted the mechanical energy 
into electric energy; actual experiments leading to the result 
that for every foot-pound of work done by the steam-engine on 
the generator, quite seven-tenths of a foot-pound of work can be 
done by the distant motor. 
One reason why electric transmi sion of power can be effected 
with so little waste is because electricity has apparently no mass, 
and consequently no inertia; there is, therefore, no waste of 
power in making it go round a corner, as there is with water or 
with any hind of material fluid. Another reason why electro- 
motors are so valuable for travelling machinery is on account of 
the light weight of the motor. Experiment shows that one 
horse-power can be developed with 56 Ibs. of dead weight of 
electro-motor, and that for large electro-motors of several horse- 
power the weight per horse is even much less; a result im- 
mensely more favourable than can be obtained with steam, gas, 
or compressed-air-engines. 
In addition to the loss of power arising from the heating of 
the wires by the passage of the current, there is another kind of 
loss that may be most serious inthe case of a long electric rail- 
way, viz., that arising from actual leakage of the electricity due 
to defective insulation. To send an electric current through a 
distant motor, two wires, a ‘‘ going” and ‘‘ return” wire mnst 
be employed, insulated from one another by silk, guttapercha, 
or some insulating substance ; and if the motor be on a moving 
train, there must be some means of keeping up continuous con- 
nection between the two ends of the moving electro-motor and the 
going and return wire. The simplest plan is to use the two rails as 
the two wires, and make connection with the motor through the 
wheels of the train ; those on one side being well insulated from 
those of the other, otherwise the current would pass through 
the axles of the wheels, instead of through the motor. It is this 
simple plan that is employed in Siemens’ Lichterfelde Electric 
Railway, now running at Berlin; the insulation arising from the 
rails being merely laid on wooden sleepers having been found 
sufficient for the short length, 14 mile. The car is similar to an 
ordinary tram-car, and holds twenty passengers. [Photographs 
were then projected on the screen of this and of the original 
electric railway laid by Siemens in the grouuds of the Berlin 
Exhibition of 1879, and exhibited in 1881 at the Crystal Palace, 
Sydenham.] It was explained that on this latter railway, which 
was goo yards long, both the ordinary rails were used as the 
return wire, and that the going wire was a third insnlated rail 
rubbed by the passing train. [Photographs were then projected 
oa the screen of Siemens’ electric tram-car at Paris, used to 
carry fifty passengers backwards and forwards last year to the 
Electrica] Exhibition.] In this the going and return wires were 
overhead and insulated, connection being maintained between 
them and the moving car by two light wires attached to the car, 
and which pulled along two little carriages running on the over- 
head insulated wires, and making electric contact with them, 
[Experiments followed, proving that although two bare wires lying 
on the ground could be quite efficiently employed as the going 
and return wire, if the wires were short and the ground dry, 
the leakage that occurred if the wires were long and the ground 
moist was so great, as to more than compensate for the absence 
of the locomotive. ] Consequently Prof. Perry and myself have 
for some time past been working out practical means for over- 
coming these difficulties, and we have arrived at what we hope 
is an extremely satisfactory solution. Instead of supplying 
electricity to one very long, not very well insulated rail, we lay 
by the side of our railway line a well insulated cable, which 
conveys the main current. The rail, which is rubbed by the 
moving train, and which supplies it with electric energy, we 
subdivide into a number of sections, each fairly well insulated 
from its neighbour and from the ground ; and we arrange that 
at any moment only that section or sections, which is in the 
immediate neighbourhood of the train, is connected with the 
main cable; the connection being of course made automatically 
by the moving train. As then leakage to the earth of the 
strong propelling electric current can only take place from that 
section or sections of the rail, which is in the immediate neigh- 
bourhood of the train, the loss of power by leakage is very much 
less than in the case of a single imperfectly insulated rail such 
as has been hitherto employed, and which being of great length, 
with its correspondingly large number of points of support, 
would offer endless points of escape to the motive current. 
Dr. Siemens has experimentally demonstrated that an electric 
railway can be used fora mile or two; Prof, Perry and myself, 
by keeping in mind the two essentials of success, viz. attention 
to both the mechanical and electrical details, have, we venture to 
think, devised means for reducing the leakage on the longest 
railway to less than what it would be on the shortest. 
For the purpose of automatically making connection between 
the main well-insulated cable and the rubbed rail in the neigh- 
bourhood of the moving train we have devised various means, 
one of which is seen from the following figures. 
AB (Fig. 1) is a copper or other metallic rod resting on the top 
of and fastened to a corrugated tempered steel disc DD (of the 
nature of, but of course immensely stronger than the corru- 
gated top of the vacuum box of an aneroid barometer), and 
which is carried by and fastened to a thick ring EE made of 
ebonite or other insulating material. The ebonite ring is itself 
screwed to the circular cast-iron box, which latter is fastened to 
