thus anticipated by about thirteen years the practically simultaneous discoveries
of Varley, AVheatstone and Siemens."
"With this brilliant exception, and that of another inventor, who in
1858 also proposed "to employ the electro-magnet in obtaining induced
electricity which supplies wholly or partially the electricity necessary for
polarizing the electric magnets, which electricity would otherwise be required
to be obtained from batteries and other known sources," inventors confined
themselves for the next ten years to the perfection of magneto-electric
machines. It will be seen from the necessarily brief accounts here given
that most of the early attempts, however ingenious, at mechanical productions
of electric currents, proved unpractical ; some few bearing the stamp of genius
are clearly anticipatory of later and successful developments ; others, again,
dating from this early period, have steadily developed into the practical types
of to-day. But, with few exceptions, the interest attaching to the inventions
and propositions prior to 1870 is mainly historical. With that date, however,
the problem of producing electrical currents by mechanical means enters a
new phase, and with the first patent of Gramme this branch of science
commences a fresh epoch.
The honor of devising a practical generator, yielding absolutely
continuous currents, belongs, without doubt, to M. Zenobie Theophile
Gramme, of Paris. His first patent was taken out in 1870; and his first
machine was submitted to the Academy of Science in July, 1871, when it
elicited warm commendations from the members of that learned body.
Adopting the sof.t iron ring of Paciriotti, he wrapped around it consecutive
lengths of insulated wire, thus forming a number of short distinct coils.
The ends of these were brought out and formed into one circuit, by joining
with metallic sectors, which were themselves connected with the novel
commuting arrangements of the machine. Gramme afterwards made several
improvements on his original machine, but it would be impossible to give
their details in this sketch in a way to be generally understood.
PRACTICAL DYNAMO BUILDING. 121
Suffice it to say, that from this new departure of Gramme has directly
sprung our present methods of producing electricity at a cost, even now,
below the price for which the same quantity of light from gas can be furnished
the public. Thus we see that while machines furnished with permanent steel
magnets succeeded chemical batteries for the production of electric light, these
in their turn were succeeded by machines (now generally known as dynamos) ,
containing electro-magnets of soft iron, which have been found to be capable
of holding twenty times as much magnetism as permanent magnets. The
accumulation of electricity by means of a dynamo machine is based upon two
principles :
First. That when a wire is moved across a magnet through a space
surrounding the magnet, and known as " the field of force," the power exerted
against the attraction of the magnet is converted into electricity.
Second. When an electric current is passed through insulated wires,
coiled around a piece of iron, the iron is magnetized.
In treating of the subsequent discoveries of Siemens and Wheatstone,
Prof. Tyndall, in a discourse delivered at the Royal Institution of Great
Britain, January 17th, 1879, said: " On the 4th of February, 1867, a paper
was received by the Royal Society from Mr. William Siemens, bearing the title,
' On the Conversion of Dynamic into Electrical Force without the use of
Permanent Magnetism.' On the 14th of February, a paper from Sir Charles
Wheatstone was received, bearing the title, i 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. The whole field of science hardly furnishes 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 small beginnings 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 the latter to
122 PRACTICAL DYNAMO BUILDING.
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
the 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 around 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.
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 electric
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."
Since the discoveries of Siemens and Wheatstone there have been many
improvements made in dynamo -electric generators, and the number of different
inventions made is very large. In Europe the number is far greater than
here. In America the best know are the Brush, Edison, Excelsior, Fuller,
Heisler, Jenney, Maxim, Sperry, Thomson-Houston, Van Depoele and
Weston.
In the line of conductors for arc lamps great progress has been made.
It is not more than eight or nine years since the separation of generator and
light was made to any extent, 150 to 200 yards being the maximum. But
gradually the divisibility of the electric light in separating the lamps fed
from the same generator, resulted in the necessary consequence of extending
the radius of operations of one installation, and consequently the length of
the conductors became more and more extended. This led to a search for
the best and most available material for conductors and silver was found to
PRACTICAL DYNAMO BUILDING 123
be the best. Its cost, however, precluded its use, and copper the next
metal in conductibility was selected. The size of the copper wires or
conductors is varied according 1 to the kind of electric light supplied through
them. The conductors for the incandescent system must be comparatively
large, for the volume of electricity is greater in it than in the arc system.
The arc lights, which require a more intense current, do not need so
large conductors, though some require or use larger wires than others. These
arc light wires are carefully covered with an insulating material to prevent
the current from being deflected from its intended course. There are various
substances used in coating or insulating conductors, among them being
gutta-percha, rubber, asphaltum, etc.
Perhaps it may not be out of place here to state that the first
fundamental law of electric currents is that discovered by Dr. G. S. Ohm,
and known as Ohm's law. It sums up the two causes which affect the
strength of an electric current in the following statement: The strength of
a current is directly proportional to the electro-motive force that tends to
drive the current through the wires of the circuit and it is inversely
proportioned to the resistance which the whole circuit offers to the passage
of the current.
The law may be illustrated in this way: Suppose either a dynamo-
electric generator or a battery of voltaic cells be employed to send a current
through a long line of wire and a series of lamps which offer a certain
considerable resistance to the flow ; to keep this flow going in spite of the
resistance requires a continued steady pressure, as it were, behind. The name
of ' l electro-motive force ' ' is given to this particular power of the generator
or battery, by virtue of which it tends to urge electricity through the circuit.
If, through the same circuit, it is desired to send a current of double strength,
then twice as great an electro-motive force must be applied, and we must do
this either by driving our generator at double speed or by using a larger
and more powerful generator; or, in the case of a battery, doubling the
number of cells. The standard by which electro-motive force is measured is
called "one volt;" it corresponds in practice very nearly to the electro-
motive force of a single Daniells cell. The dynamo-electric generators in
124 PRACTICAL DYNAMO BUILDING.
use for electric lights urge the currents forward with electro-motive forces
that vary from fifty volts to two hundred volts, according to their construction,
etc. Within certain limits the electro-motive force for a machine of given
construction is proportional to the speed at which it is driven.
The standard hy which electric resistance is measured is, as we have
seen, denominated "one Ohm," which is approximately as great a resistance
as that offered by about one hundred yards of ordinary telegraph wire. The
arc or flame electric lamp may offer, according to circumstances, from one
to ten times.
The resistance of incandescent lamps, such as those of Swan and
Edison, ranges from thirty-five ohms in the former to one hundred and thirty
ohms in the latter. The unit or standard in which currents of different
strength are expressed is the "ampere." An electro-motive force of one
volt, when applied to drive electricity through a circuit whose resistance is
one ohm, produces therein a current whose strength is one ampere. For
producing an arc light the current must not be less than about two amperes,
and may be as great as fifty or more amperes. The current in incandescent
lamps is usually a little more than one ampere in strength. Ohm's law may
be expressed exactly as follows : the strength of the current in amperes is
found by dividing the number of volts of electro-motive force by the number
of ohms of resistance in the circuit.
Before electric conductors were perfected the arc lamp was the subject
of invention and improvement. The first arc lamp was patented by Thomas
Wright, of England, in 1845. In this the electrodes were made in form of
discs rotated by clock-work, with the slow continuous motion. In 1847 Mr.
W. E. Staite brought out a lamp in which the length of the arc was
regulated by mechanical devices. He employed carbon rods as his electrodes,
and arranged them vertically one over the other, making the feeding of them
dependent on the current traversing the circuit. From this time up to March,
187G, when Jablochkoff secured his patent for his electric candle, there were
a great number of arc lamps invented in England, France, Germany, Russia
and the United States for which patents were obtained.
The discovery of M. Jablochkoff involved the suppression of all the
PRACTICAL DYNAMO BUILDING. 125
mechanism then usually employed in ordinary electric lamps. The so-called
candle consisted of two carbons fixed parallel to each other, a slight distance
apart, and separated by an insulating material which was consumed at the
same rate as the carbons themselves. An even consumption of the carbons
was secured by alternating the direction of the flow of the current from the
generator by reversing its motion. This form of lamp was afterwards
improved, but it has not found equal favor with some others.
In a dynamo machine the magnets, when at rest, are but very feebly
magnetized ; but when the armature is revolved it generates an electric
current which passes through the wires around the magnets, increasing their
strength and enabling them to produce a stronger current in the armature ;
and this in turn adds to the strength of the magnets, the armature and the
magnets reacting on each other, until the limit of the capacity of the magnet
is reached, after several hundred revolutions of the armature. When the
motion of the armature is stopped the magnets lose nearly all their magnetism,
as soft iron will not retain magnetism like steel.
Electricity for lighting might be furnished by galvanic batteries, but
the cost would amount to twenty-five or thirty times as much as when
generated by a dynamo.
It may be further explained that an electric current, flowing in a
circuit of wire, may be regarded as a magnetic whirl in the space surrounding
the wire. If, then, by moving the coil of wire past a magnet we set up
magnetic whirls in the space surrounding the coil, we set up electric currents
in the wires themselves. Dynamo-electric generators are machines for moving
coils of wire past poles of magnets, there being special arrangements, first,
to procure the setting up of very powerful magnetic whirls around the coils
of wire, and, therefore, of very strong electric currents in the wires themselves ;
and secondly, to turn all these currents into one direction, so as to flow in
one steady stream through the circuit.
Now, in regard to the relation of electric currents to the work they
can do, and to the energy expended in their production, it is laid down as a
fundamental principle that to do work of any kind, whether mechanical or
electrical, requires the expenditure of an equivalent amount of energy. Just
126 PRACTICAL DYNAMO BUILDING.
as a steam engine cannot work without using fuel, or a laborer without food,
so an electric current cannot go on flowing, nor an electric light keep on
shedding its beams, without a supply of energy from somewhere or other.
Thus, although magnets are used in order to generate currents of
electricity in rotating coils of wire, a magnet is not in itself a source of power.
It will not do work for us until we have done an equal amount of work on it.
"We must pull its keeper away from it before it can pull the keeper back to do
work. Then it yields us in its kind. It transmutes our energy into another
form of force that can produce either light, power, or heat, according as we
desire to utilize it. It is just the same with other forces. An iron weight, for
example, is not in itself a source of power. It will not do work for us it
will not even drive a clock until we do some work on it. In generating
electric currents from electro-magnets in the manner explained, as practiced
by all the electric light companies of the day, we (our steam engines) have to
supply the necessary energy. We spend this energy in moving something in
opposition to a resisting force. This something happens to be a coil of wire,
or a combination of such coils. The force in this case happens to be a
magnetic force, and the result of the motion happens to be (by the particular
arrangements of the coils and magnets) the setting up of magnetic whirls
around the wire, or what we otherwise call an electric current in the wire.
But it is we (or our engines) that do the work.
There are two methods of converting electricity into light. The arc
light is chiefly due to the glowing of the tips of the carbons, caused by the
high temperature produced by the current overcoming the resistance offered by
the space between the carbon poles, whereby the energy of the electricity is
converted into heat. The carbons are slowly volatilized and partially burned.
The intensely heated vapor adds to the illumination ; but the combustion of the
burning carbon interferes with the light. The incandescent light is produced
by the current overcoming the resistance offered by a filament of carbon and
raising it to a temperature sufficient to render it luminous. The immediate
destruction of the carbon of the incandescent system is prevented by regulating
the quantity of the current and inclosing the carbon in a glass bulb, and
exhausting the air, so that it can not burn. Both the arc and incandescent
PRACTICAL DYNAMO BUILDING. 127
lights are due to the glowing of intensely heated carbon. In the arc light the
incandescence is, in a measure, destructive to the carbon ; but with thoroughly
homogeneous material in the carbons, and an accurate and sensitive mechanical
system of feeding, this waste can be so regulated and anticipated that no
aberrations in the illumination in the arc can occur. In the arc light, where
the carbon is heated to destruction, the total quantity of light for a given
expenditure of electricity is about nine times what it is in an incandescent light
working at a commercial rate.
Sir William Armstrong has found that six horse-powers would supply
thirty-seven incandescent lights, giving altogether the illumination of nine
hundred and twenty-five candles, while the same power applied to arc lights
would give more than six thousand candles. In the arc light the terminals of
the carbons are different, the lower carbon consuming to a sharp point, while
the upper one is blunt and the end concave. The light emitted from these
ends is not alike; the upper carbon having the most heated surface, about
nine-tenths of the light is thrown downward below a horizontal plane. This
gives the arc light advantages as an illuminant of large halls, parks, streets,
factories, etc., where it can be suspended overhead, to manifest advantage in
the distribution of the light which can all be utilized. The power of arc lights
as generally estimated, is that of the strongest rays which are thrown down at
an angle of forty-five degrees, which is about twice the brilliancy of the
average light. The temperature of the upper carbon, according to experiments
made in France, in 1879, in an electric light, is estimated at six thousand
degrees Fahrenheit, and the lower one at four thousand five hundred degrees,
but this estimate refers only to the special light experimented with, which used
small carbons ; and the general result to-day, in the opinion of electricians
is probably greater than the one given above.
Dr. "W. H. Preece estimates the temperature of the lower or negative
carbon to be about 5,702 degrees Fahrenheit, while the upper or positive
carbon has a temperature of 7,052 degrees, the arc itself being 8,672 degrees
Fahrenheit. This high temperature also furnishes much more light rays from
a given amount of heat than a lower temperature would give. Dr. Charles "W.
Siemens, in an address delivered before the British Association, in York,
128 PRACTICAL DYNAMO BUILDING.
England, two years ago, stated " that in a gas burner only one per cent of the
calorific energy of combustion produced light, while in the incandescent light
it was three and seven-tenths per cent, and in the arc light it amounted to
thirty-three per cent." This will give an idea of the relative economy of the
three systems. The incandescent light exceeds gas by nearly four to one, while
the arc light exceeds gas by thirty times, and the incandescent light by eight
times, besides giving a white, clearer and purer light than either gas or electric
incandescence. Indeed, the pure white of the electric light, compared with the
dim yellow of gas, the ability to distinguish colors, the absence of heat and
injurious effect to clothing, pictures, etc., the cleanliness and purity of the air
in halls and factories under its use, all tend to make it the most desirable of the
artificial illuminants. American Electrical Directory, 1885.
THE INCANDESCENT SYSTEM.
In Dredge's work on "Electric Illumination" Mr. Conrad "W. Cooke
gives the history of the various systems of incandescent lighting. Regarding
the Swan system and, incidentally, the Edison, we outline the most salient
features. The first published notice of the Swan incandescent lamp, according
to Mr. Cooke, appeared in the issue of the Photographic Journal for June,
1880, but Mr. Swan had publicly exhibited a carbon filament lamp, which had
given excellent results, twelve months before the above named date at the
conclusion of a lecture he delivered in Newcastle, Sir William Armstrong
having presided at this meeting. It is, therefore, an historical fact that the
Swan carbon filament incandescent lamp had been brought to a practical
form and was publicly exhibited in the autumn of 1879.
As an actual fact of much interest, Mr. Swan had been laboring at
this work of incandescent lighting for many years, one of the earliest forms
he adopted in those comparatively remote days having been a horse-shoe of
carbonized paper placed beneath a glass bell which was more or less exhausted
of air. The small arch of carbonized paper was about an inch high and half
an inch across, the lower ends were clamped to small blocks of carbon and
the bell was exhausted as far as possible of air. When an electric current
of sufficient strength was passed through this carbon strip it was, owing to
its high resistance, brought rapidly to a state of incandescence, but, naturally,
such a device had but a very short duration in service. The filament became
hotter on the inner than on the outer edge and under this unequal influence
began to curl over, rapidly bending more and more until the crown of filament
would touch the base of the lamp and break up. This, however, was in the
(129)
130 PRACTICAL DYNAMO BUILDING.
early days of Mr. Swan's experiments, which he appears to have abandoned
for a considerable time, resuming them, however, with great ardor since 1877.
Early in 1879 he realized the fact that, to obtain a durability of carbon
filament, it was necessary to maintain it at as high or a higher temperature
during the process of exhausting the air from the glass bulb than it would
have subsequently to sustain in actual work.
It was just about this time that Mr. Edison was conducting a remarkable
series of parallel experiments with platinum and its alloys, and the results
he obtained of the changed physical properties of metal wire, raised to
incandescence in vacuo, corresponded strictly to those obtained by Mr. Swan
with carbon filaments treated in a similar way. It was on the 19th of June,
1879, that Mr. Edison took out his patent in Great Britain for the application
of this principle he had discovered, for the manufacture of incandescent electric
lamps, with prepared platinum or alloyed platinum luminous loops ; but he, like
inventors twenty years before him, abandoned metallic, and availed himself of
vegetable filaments. Mr. Swan, on the other hand worked with the latter from
the beginning, and the evolution of his system from the first imperfect and
rapidly failing horseshoe of carbonized paper, to his permanent metal-like
filament of carbonized thread, is an interesting one to follow. In this
connection it may be advisable to point out, in the clearest possible manner, the
great radical distinction between the Edison lamp and the Swan lamp of the
most recent type. Edison insists upon using a "structural carbon," because
he says that such carbons alone possess the qualities of the highest possible
resistance in a very small bulk, and are capable of resisting the disintegrating
effects of intense heat, and the absence of atmospheric pressure. He further
says, that by structural carbon he means "a carbon wherein the natural
structure, cellular or otherwise, or the original material is preserved unaltered,
that is, not modified by any treatment which tends to fill up the cells or porse
with unstructural carbon, or to increase its density, or alter its resistance."
To obtain such carbons, therefore, Mr. Edison is obliged to resort to
raw material, such as natural fibre, and now exclusively to bamboo strips,
which are subjected to a series of beautiful processes. Mr. Swan's object, on
the other hand, is to obtain a material suitable for the carbon filament which
PRACTICAL DYNAMO BUILDING. 131
shall be as far as possible devoid of structure ; he could not, therefore, make
use of any vegetable fibre in its natural state. Paper he quickly found was
unsuitable, even when prepared by his special process, and he ultimately
adopted cotton thread, which is susceptible to the parchmentizing operation