NATURE 
only requires four Faure accumulators to illuminate it, this one 
eight, and this other one twelve. But must the accumulators be 
even as large as those I am using on the table? The answer is, 
No; if you do not require them to give out the light for a very long 
time. Four much smaller boxes would give just as much light 
as you see at the present moment; but, of course, would not 
keep the light burning so long. It is, therefore, now possible 
to have a box of accumulators and an incandescent lamp, and 
the whole thing quite easily carried by one man. ‘ 
Last year Prof. Perry drew attention, in his lecture at the 
Society of Arts on the ‘‘ Future of Electrical Appliances,” to the 
great waste of energy that is produced by the coal being carried 
to the steam-engine, instead of steam-engines being brought to 
the coal, and the power given out by the engines conveyed elec- 
trically to the place where it was commercially required, Why, 
said he, should not the coal be burnt at the pit’s mouth, or in the 
pit, or even in that part of the mine where the seams were 
thickest, and the engines driven by burning it used to work large 
dynamo-machines on the spot, and the power transmitted electri- 
cally to any towns where it was required? Again, it has been 
often asked, why should not the wasted power in streams be 
utilised 2? At present it is more economical to use steam-engines 
in a town than to do work in the country by means of the 
streams, and convey the manufactured articles over the hills into 
the towns ; and for that reason one sees the old water-wheels, in 
the neighbourhood of a place like Sheffield, being gradually 
deserted, and the men preferring to pay a higher rent for steam- 
driven grindstones in the town, to a smaller rent for water- 
driven grindstones in the suburbs. The question then arises 
would it be possible to convey economically the power from the 
coal-pits or from the streams into the towns by means of electricity ; 
and this obviously turns on, how much power can be got ont of 
one end of a wire compared with the amount that is put in at 
the other. 1 have, during this evening, been talking of the 
measurements of electric energy put into or taken out of an 
accumulator in foot-pounds, and you may have wondered how 
it was possible to measure electric energy in the engineer’s unit 
of foot-pounds. In reality it is very simple. The maximum 
amount of work a waterfall can do, deperds on two things, the 
current of water and the height of the fall. In the same way, 
the work a galvanic cell or accumulator can do, depends on two | 
things, the current it is producing, and what is called its electro- 
motive force, the latter being analogous with the difference of 
pressure or head of water. Again, when electric energy is being 
turned into mechanical work by means of an electro-motor, the 
energy which is being put into the motor can be measured by 
the product of the current sent through the motor, and the 
electromotive force maintained between the terminals of the 
motor. Now, here are two instruments, devised by Prof. 
Perry and myself, an Am-meter and a Volt-meter, the one for | 
measuring a strong current, and the other a large electromotive 
force. With these we will now make simultaneous measurements | 
when we allow this motor, which is driving the lathe, and which 
is itself driven by an electric current, to run at different speeds. 
First, we will start with the motor, which has one ohm resistance 
absolutely at rest, by putting a break on it, and ending by 
allowing it to run as fast as possible. 
Experiment performed and the following results were ob- 
tained :— 
Electro- 
motive force) Electric power | she current heat 
Speed of |Currentin| between | put into the motor eceecee nee Z 
motor. | Ampéres. | terminals of in foot pounds per eae ai 
- ae mUABE: pounds per minute. 
° 15 rs | J 15% 15% 44-25) 15°X 1X 44.25 
|) “te. 9956.25] te. 9956.25 
2 
Slow 10 21 TO X 21 X 44.25) 10? x I x 44.25 
1.¢. 9292. § Zé. 4425 
i 2 
Fast 4x 28 x 44 25 4° x 1x 44. 5 
4 * Zé. 4956 i.e. 708 
We see in the last case, when the load was light and the speed 
of the motor very great, there was less than one-tenth of the 
waste of power arising from the current heating the wires when 
the speed was very slow. On the other hand, we observe that 
the electro-motive force between ‘he terminals of the motor has 
been practically doubled. “ 
‘This simple experiment really roints to the solution of economic 
transmission of power by electricity, and to which Prof. Perry 
and myself have on numerous occasions directed attention, It 
is, to allow only a very small current to pass through the wires 
connecting the electro-motor with the generator, and to maintain 
a very great electro-motive force between them ; since, in this 
way, the amount of power transmitted can be made as large as 
we like, and the waste from the heating of the wires from the 
passage of the current as small as we Jike. 
Reasoning in this way, Sir W. Thomson showed, in his 
inaugural address last year to the British Association, that, if we 
desire to transmit 26,250 horse-power by a copper wire half an 
inch in diameter, from Niagara to New York, which is about 
300 miles distance, and if we desire not to lose more than one- 
fifth of the whole amount of work—that is, to deliver up in 
New York 21,000 horse-power—the electromotive force between 
the two wires must be 80,000 volts. Now, what are we to do 
with this enormous electromotive force at the New York end of 
the wires? Fancy a servant dusting a wire having this encr- 
mous electromotive force. You might as well, as far as ber 
peace of mind is concerned, ask her to put a lightning flash 
tidy. 
The solution of this problem was also given by Sir W. Thom- 
son on the same occasion, and it consists in using large numbers 
of accumulators, All that is necessary to do in order to sub- 
divide this enormous electromotive into what may be called 
small commercial electromotive forces is to keep a Faure battery 
of 40,0C0 cells always charged direct from the main current, and 
apply a methodical system of removing sets of 50 and placing 
them on the town supply circuits, while other sets of 50 are 
being regularly introduced into the main circuit that is being 
charged. Of course this removal does not mean bodiiy removal 
of the cells, but merely disconnecting the wires. It is probable 
that this employment of secondary batteries will be of great 
importance since it overcomes the last difficulty in the economical 
electrical transmission of power over long distances. 
1 will conclude my lecture by illustrating one of the other im- 
portant uses to which the accumulator can he applied, and that 
is the practical lighting of railway trains, which may be seen in 
daily oy eration in the Pullman cars on the Brighton line. The 
most natural wethod of lighting a railway train would be to 
attach a dynamo-machine to the axle of one of the carriages— 
the guard’s van, for exampie—and the rotation of which, neces- 
sarily very rapid when the train is going fast, would, without the 
use of any gearing, produce the necessary current. FEut the 
| difficulty that immediately meets us is that as soon as the train 
slows, or stops at a station, or in consequence of the signal 
being against it, the speed of the dynamo-machine will diminish 
and the lights will go out. If, however, while the train is going 
fast, the dynamo performs two operations, the one to keep the 
lights burning, the other to charge a battery of Faure’s accumu- 
lators on the train, then the electric energy so stored can be 
applied to maintain the lights while the train is going slowly or 
stopping. With such an arrangement there would be, of course, 
an automatic contrivance for disconnecting the dynamo-machine 
from the circuit when the speed becomes too low ; otherwise the 
Faure’s accumulators would simply discharge themselves back 
through the dynamo-machine. 
Imagine, now, we are in a train which is going slowly, or 
which has actually stopped, and that the Faure accumulators 
lying here on the floor is the Faure battery ‘in the train, and 
which have been charged when the train was going fast; then 
that it has sufficient store of energy to continue lighting is 
proved, because, on connecting these two wires, those fifty 
Maxim lamps, kindly lent me by the Electric Light and Power 
Company, and eight Edison lamps before you, are instantly 
brilliantly illuminated, each of the former possessing about 
forty candle-power, and each of the latter about seventeen, 
and giving, therefore, far more light than is, at present, ever 
cupplied to a whole train of twelve carriages. The light, you 
observe, is perfectly steady, and is turned on and off at will. 
Imagine, now, we are in a tunnel in the daytime, and the lights, 
therefore, burning. We now emerge from thc tunnel into day- 
light. 1 disconnect the wires, and the lights are instantly extin- 
guished. Again, it may be we are entering a second tunnel. 
The wires are again connected by the guard, and we have the 
whole of this lecture-theatre, which represents the train, bril- 
liantly illuminated. 
rae 
[March 23) 1882 B 
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