really constitutes an important step in the development of this
subject. I refer to the form given in 1857 to the rotating armature
by Dr. Werner Siemens, of Berlin. Instead of employing coils wound
transversely round cores of iron, as in the machine of Saxton,
Siemens, after giving a bar of iron the proper shape, wound his wire
longitudinally round it, and obtained thereby greatly augmented
effects between suitably placed magnetic poles. Such an armature is
employed in the small magneto-electric machine which I now introduce
to your notice, and for which the institution is indebted to Mr. Henry
Wilde, of Manchester. There are here sixteen permanent horse-shoe
magnets placed parallel to each other, and between their poles a
Siemens armature. The two ends of the wire which surrounds the
armature are now disconnected. In turning the handle and causing the
armature to rotate, I simply overcome ordinary mechanical friction.
But the two ends of the armature coil can be united in a moment, and
when this is done I immediately experience a greatly increased
resistance to rotation. Something over and above the ordinary
friction of the machine is now to be overcome, and by the expenditure
of an additional amount of muscular force I am able to overcome it.
The excess of labour thus thrown upon my arm has its exact equivalent
in the electric currents generated, and the heat produced by their
subsidence in the coil of the armature. A portion of this heat may be
rendered visible by connecting the two ends of the coil with a thin
platinum wire. When the handle of the machine is rapidly turned the
wire glows, first with a red heat, then with a white heat, and finally
with the heat of fusion. The moment the wire melts, the circuit round
the armature is broken, an instant relief from the labour thrown upon
the arm being the consequence. Clearly realise the equivalent of the
heat here developed. During the period of turning the machine a
certain amount of combustible substance was oxidised or burnt in the
muscles of my arm. Had it done no external work, the matter consumed
would have produced a definite amount of heat. Now, the muscular heat
actually developed during the rotation of the machine fell short of
this definite amount, the missing heat being reproduced to the last
fraction in the glowing platinum wire and the other parts of the
machine. Here, then, the electric current intervenes between my
muscles and the generated heat, exactly as it did a moment ago between
the voltaic battery and its generated heat. The electric current is
to all intents and purposes a vehicle which transports the heat both
of muscle and battery to any distance from the hearth where the fuel
is consumed. Not only is the current a messenger, but it is also an
intensifier of magical power. The temperature of my arm is, in round
numbers, 100° Fahr, and it is by the intensification of this heat that
one of the most refractory of metals, which requires a heat of 3,600°
Fahr. to fuse it, has been reduced to the molten condition.
Zinc, as I have said, is a fuel far too expensive to permit of the
electric light produced by its combustion being used for the common
purposes of life, and you will readily perceive that the human
muscles, or even the muscles of a horse, would be more expensive
still. Here, however, we can employ the force of burning coal to turn
our machine, and it is this employment of our cheapest fuel, rendered
possible by Faraday's discovery, which opens out to us the prospect of
being able to apply the electric light to public use.
In 1866 a great step in the intensification of induced currents, and
the consequent augmentation of the magneto-electric light, was taken
by Mr. Henry Wilde. It fell to my lot to report upon them to the
Royal Society, but before doing so I took the trouble of going to
Manchester to witness Mr. Wilde's experiments. He operated in this
way: starting from a small machine like that worked in your presence a
moment ago, he employed its current to excite an electro-magnet of a
peculiar shape, between whose poles rotated a Siemens armature;
[Footnote: Page and Moigno had previously shown that the
magneto-electric current could produce powerful electro-magnets.] from
this armature currents were obtained vastly stronger than those
generated by the small magneto-electric machine. These currents might
have been immediately employed to produce the electric light; but
instead of this they were conducted round a second electro-magnet of
vast size, between whose poles rotated a Siemens armature of
corresponding dimensions. Three armatures therefore were involved in
this series of operations: first, the armature of the small
magneto-electric machine; secondly, the armature of the first
electro-magnet, which was of considerable size; and, thirdly, the
armature of the second electro-magnet, which was of vast dimensions.
With the currents drawn from this third armature, Mr. Wilde obtained
effects, both as regards heat and light, enormously transcending those
previously known. [Footnote: Mr. Wilde's paper is published in the
'Philosophical Transactions 'for 1867, p. 89. My opinion regarding
Wilde's machine was briefly expressed in a report to the Elder
Brethren of the Trinity House on May 17, 1866: 'It gives me pleasure
to state that the machine is exceedingly effective, and that it far
transcends in power all other apparatus of the kind.']
But the discovery which, above all others, brought the practical
question to the front is now to be considered. On the 4th of
February, 1867, a paper was received by the Royal Society from Dr.
William Siemens bearing the title, 'On the Conversion of Dynamic into
Electrical Force without the use of Permanent Magnetism.' [Footnote: A
paper on the same subject, by Dr. Werner Siemens, was read on January
17, 1867, before the Academy of Sciences in Berlin. In a letter to
'Engineering,' No. 622, p. 45, Mr. Robert Sabine states that
Professor Wheatstone's machines were constructed by Mr. Stroh in the
months of July and August, 1866. I do not doubt Mr. Sabine's
statement; still it would be dangerous in the highest degree to depart
from the canon, in asserting which Faraday was specially strenuous,
that the date of a discovery is the date of its publication. Towards
the end of December, 1866, Mr. Alfred Varley' also lodged a
provisional specification (which, I believe, is a sealed document)
embodying the principles of the dynamo-electric machine, but some
years elapsed before he made anything public. His brother, Mr.
Cromwell varlet', when writing on this subject in 1867, does not
mention him (Proc. Roy. Soc, March 14, 1867). It probably marks a
national trait, that sealed communications, though allowed in France,
have never been recognised by the scientific societies of England.] On
the 14th of February a paper from Sir Charles Wheatstone was received,
bearing the title, 'On the Augmentation of the Power of a Magnet by
the reaction thereon of Currents induced by the Magnet itself.' Both
papers, which dealt with the same discovery, and which were
illustrated by experiments, were read upon the same night, viz. the
14th of February. It would be difficult to find in the whole field of
science a more beautiful example of the interaction of natural forces
than that set forth in these two papers. You can hardly find a bit of
iron--you can hardly pick up an old horse-shoe, for example--that does
not possess a trace of permanent magnetism; and from such a small
beginning Siemens and Wheatstone have taught us to rise by a series of
interactions between magnet and armature to a magnetic intensity
previously unapproached. Conceive the Siemens armature placed between
the poles of a suitable electro-magnet. Suppose this latter to possess
at starting the faintest, trace of magnetism; when the armature
rotates, currents of infinitesimal strength are generated in its coil.
Let the ends of that coil be connected with the wire surrounding the
electro-magnet. The infinitesimal current generated in the armature
will then circulate round the magnet, augmenting its intensity by an
infinitesimal amount. The strengthened magnet instantly reacts upon
the coil which feeds it, producing a current of greater strength.
This current again passes round the magnet, which immediately brings
its enhanced power to bear upon the coil. By this play of mutual give
and take between magnet and armature, the strength of the former is
raised in a very brief interval from almost nothing to complete
magnetic saturation. Such a magnet and armature are able to produce
currents of extraordinary power, and if an electric lamp be introduced
into the common circuit of magnet and armature, we can readily obtain
a most powerful light. [Footnote: In 1867 Mr. Ladd introduced the
modification of dividing the armature into two separate coils, one of
which fed the electro-magnets, while the other yielded the induced
currents.] By this discovery, then, we are enabled to avoid the
trouble and expense involved in the employment of permanent magnets;
we are also enabled to drop the exciting magneto-electric machine, and
the duplication of the electro-magnets. By it, in short, the electric
generator is so far simplified, and reduced in cost, as to enable
electricity to enter the lists as the rival of our present means of
illumination.
Soon after the announcement of their discovery by Siemens and
Wheatstone, Mr. Holmes, at the instance of the Elder Brethren of the
Trinity House, endeavoured to turn this discovery to account for
lighthouse purposes. Already, in the spring of 1869, he had
constructed a machine which, though hampered with defects, exhibited
extraordinary power. The light was developed in the focus of a
dioptric apparatus placed on the Trinity Wharf at Blackwall, and
witnessed by the Elder Brethren, Mr. Douglass, and myself, from an
observatory at Charlton, on the opposite side of the Thames. Falling
upon the suspended haze, the light illuminated the atmosphere for
miles all round. Anything so sunlike in splendour had not, I imagine,
been previously witnessed. The apparatus of Holmes, however, was
rapidly distanced by the safer and more powerful machines of Siemens
and Gramme.
As regards lighthouse illumination, the next step forward was taken by
the Elder Brethren of the Trinity House in 1876-77. Having previously
decided on the establishment of the electric light at the Lizard in
Cornwall, they instituted, at the time referred to, an elaborate
series of comparative experiments wherein the machines of Holmes, of
the Alliance Company, of Siemens, and of Gramme, were pitted against
each other. The Siemens and the Gramme machines delivered direct
currents, while those of Holmes and the Alliance Company delivered
alternating currents. The light of the latter was of the same
intensity in all azimuths; that of the former was different in
different azimuths, the discharge being so regulated as to yield a
gush of light of special intensity in one direction. The following
table gives in standard candles the performance of the respective
machines:
Name of Machines. Maximum. Minimum.
Holmes 1,523 1,523
Alliance 1,953 1,953
Gramme (No. 1). 6,663 4,016
Gramme (No. 2). 6,663 4,016
Siemens (Large) 14,818 8,932
Siemens (Small, No. 1) 5,539 3,339
Siemens (Small, No. 2) 6,864 4,138
Two Holmes's coupled 2,811 2,811
Two Gramme's (Nos. 1 and 2) 11,396 6,869
Two Siemens' (Nos. 1 and 2) 14,134 8,520
[Footnote: Observations from the sea on the night of November 21,
1876, made the Gramme and small Siemens practically equal to the
Alliance. But the photometric observations, in which the external
resistance was abolished, and previous to which the light-keepers had
become more skilled in the management of the direct current, showed
the differences recorded in the table. A close inspection of these
powerful lights at the South Foreland caused my face to peel, as if it
had been irritated by an Alpine sun.]
These determinations were made with extreme care and accuracy by Mr.
Douglass, the engineer-in-chief, and Mr. Ayres, the assistant engineer
of the Trinity House. It is practically impossible to compare
photo-metrically and directly the flame of the candle with these
sun-like lights. A light of intermediate intensity--that of the
six-wick Trinity oil lamp--was therefore in the first instance
compared with the electric light. The candle power of the oil lamp
being afterwards determined, the intensity of the electric light
became known. The numbers given in the table prove the superiority of
the Alliance machine over that of Holmes. They prove the great
superiority both of the Gramme machine and of the small Siemens
machine over the Alliance. The large Siemens machine is shown to
yield a light far exceeding all the others, while the coupling of two
Grammes, or of two Siemens together, here effected for the first time,
was followed by a very great augmentation of the light, rising in the
one case from 6663 candles to 11,396, and in the other case from 6864
candles to 14,134. Where the arc is single and the external
resistance small, great advantages attach to the Siemens light. After
this contest, which was conducted throughout in the most amicable
manner, Siemens machines of type No. 2 were chosen for the Lizard.
[Footnote: As the result of a recent trial by Mr. Schwendler, they
have been also chosen for India.]
*****
We have machines capable of sustaining a single light, and also
machines capable of sustaining several lights. The Gramme machine,
for example, which ignites the Jablochkoff candles on the Thames
Embankment and at the Holborn Viaduct, delivers four currents, each
passing through its own circuit. In each circuit are five lamps
through which the current belonging to the circuit passes in
succession. The lights correspond to so many resisting spaces, over
which, as already explained, the current has to leap; the force which
accomplishes the leap being that which produces the light. Whether
the current is to be competent to pass through five lamps in
succession, or to sustain only a single lamp, depends entirely upon
the will and skill of the maker of the machine. He has, to guide him,
definite laws laid down by Ohm half a century ago, by which he must
abide.
Ohm has taught us how to arrange the elements of a Voltaic battery so
as to augment indefinitely its electromotive force--that force,
namely, which urges the current forward and enables it to surmount
external obstacles. We have only to link the cells together so that
the current generated by each cell shall pass through all the others,
and add its electro-motive force to that of all the others. We
increase, it is true, at the same time the resistance of the battery,
diminishing thereby the quantity of the current from each cell, but we
augment the power of the integrated current to overcome external
hindrances. The resistance of the battery itself may, indeed, be
rendered so great, that the external resistance shall vanish in
comparison. What is here said regarding the voltaic battery is
equally true of magneto-electric machines. If we wish our current to
leap over five intervals, and produce five lights in succession, we
must invoke a sufficient electromotive force. This is done through
multiplying, by the use of thin wires, the convolutions of the
rotating armature as, a moment ago, we augmented the cells of our
voltaic battery. Each additional convolution, like each additional
cell, adds its electro-motive force to that of all the others; and
though it also adds its resistance, thereby diminishing the quantity
of current contributed by each convolution, the integrated current
becomes endowed with the power of leaping across the successive spaces
necessary for the production of a series of lights in its course. The
current is, as it were, rendered at once thinner and more piercing by
the simultaneous addition of internal resistance and electro-motive
power. The machines, on the other hand, which produce only a single
light have a small internal resistance associated with a small
electro-motive force. In such machines the wire of the rotating
armature is comparatively short and thick, copper riband instead of
wire being commonly employed. Such machines deliver a large quantity
of electricity of low tension--in other words, of low leaping power.
Hence, though competent when their power is converged upon a single
interval, to produce one splendid light, their currents are unable to
force a passage when the number of intervals is increased. Thus, by
augmenting the convolutions of our machines we sacrifice quantity and
gain electro-motive force; while by lessening the number of the
convolutions, we sacrifice electro-motive force and gain quantity.
Whether we ought to choose the one form of machine or the other
depends entirely upon the external work the machine has to perform. If
the object be to obtain a single light of great splendour, machines of
low resistance and large quantity must be employed. If we want to
obtain in the same circuit several lights of moderate intensity,
machines of high internal resistance and of correspondingly high
electro-motive power must be invoked.
When a coil of covered wire surrounds a bar of iron, the two ends of
the coil being connected together, every alteration of the magnetism
of the bar is accompanied by the development of an induced current in
the coil. The current is only excited during the period of magnetic
change. No matter how strong or how weak the magnetism of the bar may
be, as long as its condition remains permanent no current is
developed. Conceive, then, the pole of a magnet placed near one end
of the bar to be moved along it towards the other end. During the
time of the pole's motion there will be an incessant change in the
magnetism of the bar, and accompanying this change we shall have an
induced current in the surrounding coil. If, instead of moving the
magnet, we move the bar and its surrounding coil past the magnetic
pole, a similar alteration of the magnetism of the bar will occur, and
a similar current will be induced in the coil. You have here the
fundamental conception which led M. Gramme to the construction of his
beautiful machine. [Footnote: 'Comptes Rendus,' 1871, p. 176. See
also Gaugain on the Gramme machine, 'Ann. de Chem. et de Phys,'
vol. xxviii. p. 324] He aimed at giving continuous motion to such
a bar as we have here described; and for this purpose he bent it into
a continuous ring, which, by a suitable mechanism, he caused to rotate
rapidly close to the poles of a horse-shoe magnet. The direction of
the current varied with the motion and with the character of the
influencing pole. The result was that the currents in the two
semicircles of the coil surrounding the ring flowed in opposite
directions. But it was easy, by the mechanical arrangement called a
commutator, to gather up the currents and cause them to flow in the
same direction. The first machines of Gramme, therefore, furnished
direct currents, similar to those yielded by the voltaic pile. M.
Gramme subsequently so modified his machine as to produce alternating
currents. Such alternating machines are employed to produce the
lights now exhibited on the Holborn Viaduct and the Thames Embankment.
Another machine of great alleged merit is that of M. Lontin. It
resembles in shape a toothed iron wheel, the teeth being used as
cores, round which are wound coils of copper wire. The wheel is
caused to rotate between the opposite poles of powerful
electromagnets. On passing each pole the core or tooth is strongly
magnetised, and instantly evokes in its surrounding coil an induced
current of corresponding strength. The currents excited in
approaching to and retreating from a pole, and in passing different
poles, move in opposite directions, but by means of a commutator these
conflicting electric streams are gathered up and caused to flow in a
common bed. The bobbins, in which the currents are induced, can be so
increased in number as to augment indefinitely the power of the
machine. To excite his electro-magnets, M. Lontin applies the
principle of Mr. Wilde. A small machine furnishes a direct current,
which is carried round the electro-magnets of a second and larger
machine. Wilde's principle, it may be added, is also applied on the
Thames Embankment and the Holborn Viaduct; a small Gramme machine
being used in each case to excite the electro-magnets of the large
one.
The Farmer-Wallace machine is also an apparatus of great power. It
consists of a combination of bobbins for induced currents, and of
inducing electro-magnets, the latter being excited by the method
discovered by Siemens and Wheatstone. In the machines intended for
the production of the electric light, the electromotive force is so
great as to permit of the introduction of several lights in the same
circuit. A peculiarly novel feature of the Farmer-Wallace system is
the shape of the carbons. Instead of rods, two large plates of
carbons with bevelled edges are employed, one above the other. The
electric discharge passes from edge to edge, and shifts its position
according as the carbon is dissipated. The duration of the light in
this case far exceeds that obtainable with rods. I have myself seen
four of these lights in the same circuit in Mr. Ladd's workshop in the
City, and they are now, I believe, employed at the Liverpool Street
Station of the Metropolitan Railway. The Farmer-Wallace 'quantity
machine' pours forth a flood of electricity of low tension. It is
unable to cross the interval necessary for the production of the
electric light, but it can fuse thick copper wires. When sent through
a short bar of iridium, this refractory metal emits a light of
extraordinary splendour. [Footnote: The iridium light was shown by Mr.
Ladd. It brilliantly illuminated the theatre of the Royal
Institution.]
The machine of M. de Méritens, which he has generously brought over
from Paris for our instruction, is the newest of all. In its
construction he falls back upon the principle of the magneto-electric
machine, employing permanent magnets as the exciters of the induced
currents. Using the magnets of the Alliance Company, by a skilful
disposition of his bobbins, M. de Méritens produces with eight magnets
a light equal to that produced by forty magnets in the Alliance
machines. While the space occupied is only one-fifth, the cost is
little more than one-fourth of the latter. In the de Méritens machine
the commutator is abolished. The internal heat is hardly sensible,
and the absorption of power, in relation to the effects produced, is
small. With his larger machines M. de Méritens maintains a
considerable number of lights in the same circuit. [Footnote: The
small machine transforms one-and-a-quarter horse-power into heat and
light, yielding about 1,900 candles; the large machine transforms
five-horse power, yielding about 9,000 candles.]
*****
In relation to this subject, inventors fall into two classes, the
contrivers of regulators and the constructors of machines. M. Rapieff
has hitherto belonged to inventors of the first class, but I have
reason to know that he is engaged on a machine which, when complete,
will place him in the other class also. Instead of two single carbon
rods, M. Rapieff employs two pairs of rods, each pair forming a V. The
light is produced at the common junction of the four carbons. The
device for regulating the light is of the simplest character. At the
bottom of the stand which supports the carbons are two small
electro-magnets. One of them, when the current passes, draws the
carbons together, and in so doing throws itself out of circuit,
leaving the control of the light to the other. The carbons are caused
to approach each other by a descending weight, which acts in
conjunction with the electro-magnet. Through the liberality of the
proprietors of the Times, every facility has been given to M. Rapieff
to develope and simplify his invention at Printing House Square. The
illumination of the press-room, which I had the pleasure of
witnessing, under the guidance of M. Rapieff himself, is extremely
effectual and agreeable to the eye. There are, I believe, five lamps
in the same circuit, and the regulators are so devised that the
extinction of any lamp does not compromise the action of the others.
M. Rapieff has lately improved his regulator.
Many other inventors might here be named, and fresh ones are daily
crowding in. Mr. Werdermann has been long known in connection with
this subject. Employing as negative carbon a disc, and as positive
carbon a rod, he has, I am assured, obtained very satisfactory
results. The small resistances brought into play by his minute arcs
enable Mr. Werdermann to introduce a number of lamps into a circuit
traversed by a current of only moderate electro-motive power. M.
Reynier is also the inventor of a very beautiful little lamp, in which
the point of a thin carbon rod, properly adjusted, is caused to touch
the circumference of a carbon wheel which rotates underneath the
point. The light is developed at the place of contact of rod and
wheel. One of the last steps, though I am informed not quite the
last, in the improvement of regulators is this: The positive carbon
wastes more profusely than the negative, and this is alleged to be due
to the greater heat of the former. It occurred to Mr. William Siemens
to chill the negative artificially, with the view of diminishing or
wholly preventing its waste. This he accomplishes by making the
negative pole a hollow cone of copper, and by ingeniously discharging
a small jet of cold water against the interior of the cone. His
negative copper is thus caused to remain fixed in space, for it is not
dissipated, the positive carbon only needing control. I have seen
this lamp in action, and can bear witness to its success.