By A. A. CAMPBELL SWINTON.
It seems at present that electricity is to be the illuminating agent
of the future, and that, as gas has now all but superseded candles and
oil, so in turn gas will soon be superseded by electricity. The reasons
for this change are several and various, and follow that most immutable
of natural laws, the law of the survival of the fittest.
About the commencement of the present century, Sir Humphry Davy, the
eminent chemist, succeeded in producing at the Royal Institution the
most brilliant light then known. By passing the electricity derived
from an enormous battery of four thousand plates through two charcoal
points separated from one another, he obtained in air a continuous
electric discharge four inches in length, which was increased to seven
inches when the experiment was repeated _in vacuo_.
This discharge, or arc, as it is called, consisted of very minute
particles of charcoal, which being raised to white heat by the
resistance offered by the points to the electric current, were also by
its means conveyed with great rapidity from one charcoal point to the
other, emitting during their passage a light of dazzling brilliancy.
The discharge of heated particles being continuous, the arc could be
maintained for a considerable length of time.
This light, however, was entirely impracticable for any but purely
experimental purposes. A battery of four thousand plates is not
easily maintained in working order, and besides, the expense of such
an arrangement puts it entirely out of the question. Of late years,
however, a new method of producing electricity on a large scale has
been discovered in the dynamo-electric machine, by means of which
currents of great volume and intensity can be obtained from the power
generated by a steam engine, water wheel, or other prime motor.
This great discovery instigated scientific men to try and bring the
electric light within the range of practical utility, in which end they
have already been eminently successful.
It was found that as the charcoal points in Davy’s lamp in process of
time became oxidized and burnt away, it was necessary to have some
arrangement by which they should be maintained at a constant distance
from one another. This problem was first solved by Duboscq, a French
_savant_, who by the combined action of the electric current and a
system of clockwork, succeeded in obtaining a constant and steady
light. Gas carbon, as found incrusted on the inside of gas retorts, was
at the same time substituted for the charcoal employed by Davy, as it
was found to burn more equally and to last much longer.
In July, 1877, a new form of electric light apparatus was introduced
into France and elsewhere, which, from its practical simplicity,
attracted a large amount of attention. This invention is due to Mr.
Jablochkoff, a Russian engineer, and is known as the Jablochkoff
candle. In this form of regulator all clockwork and mechanism are
avoided; the two carbons are placed side by side, in parallel lines,
and are separated by some substance which, though readily fusible,
at the same time offers so enormous a resistance to the passage of
the electric current as practically to prevent its passage through it
at all. Kaolin clay and plaster of Paris have both been employed for
this purpose with success. The current not being able to pass through
the insulating material, can only pass between the two carbons at the
extremity of the candle, where the arc is therefore formed. As the
carbons burn away, the insulating material melts, and an uninterrupted
light is obtained. As it is found that one carbon burns away more
quickly than the other, in this form of lamp the electric current is
supplied alternately in different directions, which makes the carbons
burn equally, the reversions of the electricity being so rapid that
the arc is to all appearances continuous. This lamp has been largely
employed in Paris, and is at present in actual operation on the Thames
embankment. Its chief defects are its great expense and the unsteady
character of the light, which, owing to the oxidation of the insulating
material, flickers and changes color. Another lamp, and one which has
been largely used in Europe and in America, is the Brush regulator,
called after its inventor. In this form the carbons are vertically
one above the other, the upper one being controlled by an electro
magnet, which supports it, allowing it to descend of its own weight
when, through the distance between the carbons becoming too great, the
current is weakened, and the magnet unable to support its load, thus
keeping the arc of a constant length. There are a large number of other
arc regulators, some of which work very well, and are largely employed;
but they are most of them based on a very similar principle to that of
the Brush lamp, and therefore they need no special description.
It has been found, however, that, adapted as some of the arc regulators
are for the illumination of streets and large areas, none of them are
at all able to compete with gas in the lighting of private houses. Not
only do they require the constant attention of skilled workmen to renew
the carbons and to clean the mechanism, but they give far too strong
and dazzling a light for any but very large apartments.
For domestic lighting we therefore come to quite a new departure in
electric lamps; instead of the arc we have the incandescent regulator.
If an intense electric current be transmitted through a fine platinum
wire, the latter will, in a very few seconds, become white hot, and
give a considerable amount of light. If such a platinum wire be
enclosed in a glass globe, from which the air has been extracted, we
have one kind of incandescent lamp, so called because the light is
produced through the incandescence or intense heating of a platinum
or other conductor. It was a lamp such as this that, when brought out
by Mr. Edison two years ago, produced such a scare among holders of
gas shares. It was not, however, a practical invention; it was found
that the electric current constantly melted the platinum, or broke the
glass envelope, after which the lamp was of course entirely useless. In
vain Mr. Edison tried various alloys of platinum and iridium; nothing
of that nature was found that could resist the intense heat produced
by the electricity. While, however, the incandescent lamp was not
progressing very rapidly in America, in England Mr. Swan, of Newcastle,
who had been experimenting with the electric light for some time,
brought out another kind of regulator, which has given rise to great
expectations. The Swan lamp consists of a pear-shaped globe, blown out
of glass, and from which all the air, or at least as much as can be,
has been exhausted. In this globe there is a tiny carbon filament,
manufactured of carbonized thread, in the form of a loop, which is
attached to two platinum wires which project through the glass bulb. On
an electric current being passed through the carbon, by means of wires
attached to the platinum projections, a soft yet brilliant light is
obtained. These lamps, which give a light corresponding in power and
color to an ordinary gas flame, can now be obtained for five shillings
each, and it is probable that this price may yet be still further
reduced.
Mr. Edison also, having abandoned his earlier platino-iridium
regulator, has brought out another lamp very similar to Mr. Swan’s. In
his case the carbon filament is formed of carbonized bamboo, and the
glass bulb is of an elongated form. Incandescent lamps have also been
invented by Maxim, Crooks, Fox Lane, and others; but they only differ
in details of manufacture from those of Swan and Edison.
Among edifices now entirely illuminated by the Swan system may be
mentioned twenty-one steam vessels, including several war ships—the
_City of Rome_, an Anchor Liner, which is second only to the _Great
Eastern_ in point of size, and several passenger boats in the Cunard
and White Star Lines.
One of the greatest objections to gas as an indoor illuminant is the
fact that not only does it burn a large amount of the oxygen of the
air, but it also gives off during combustion carbonic acid gas and
other poisonous vapors, besides a great amount of heat, thus vitiating
the atmosphere. In public buildings where there is much gas burnt
and little ventilation, this is seen to advantage, the air becoming
in a short space of time hot and unwholesome. Now in the case of
the incandescent electric light, this is altogether altered, the
incandescent filament which produces the light, although in itself
enormously hot, is too small in point of size to radiate much heat,
and the fact of its being hermetically enclosed in a glass globe,
which is impervious to the atmosphere, entirely prevents the escape
of any noxious gases. The same circumstance prevents there being any
consumption of oxygen.
These facts make the electric light far more wholesome than gas for the
illumination of music-halls, churches, or other places of concourse. In
a recent trial in the Town Hall at Birmingham, the employment of gas
raised the temperature of the atmosphere thirty-eight degrees in three
hours, while the building was equally well lighted with electricity for
seven hours with a rise in temperature of only two degrees. Thus, after
a period of lighting by electricity 2.33 times as long as by gas, the
temperature at the ceiling was increased by only 1-19th of the amount
due to gas.
Another great advantage consequent to the employment of incandescent
lighting, is the greater immunity from accidental fire; for as the
carbon filament is instantly entirely consumed, the moment the glass
envelope is broken it is impossible for the lamp to ignite anything
in its vicinity however inflammable. The experiment has been tried of
breaking a lighted incandescent lamp in a vessel containing gunpowder,
with perfect safety. As these lamps may be placed in any position, they
lend themselves very readily to ornamental and decorative purposes. At
the recent electrical exhibition at the Crystal Palace a very beautiful
chandelier of Edison lamps was shown, in which the lamps, which were
of very small size, formed the petals of finely worked glass and brass
flowers. This chandelier had a really magnificent effect when lighted.
These and other facts too numerous to mention, demonstrate that
electricity, when properly applied, will be a far more elegant, safe,
and wholesome agent for illuminating purposes, than coal-gas as now
employed. But in order to have the full benefits of its use, a system
is required by which the electric current shall be produced and
conveyed to the lamps.
Not only has Mr. Edison invented an incandescent lamp, but he has also
identified his name with a very complete system for producing the light
on a large scale to suit both domestic and commercial requirements.
In the first place he has invented a peculiar form of dynamo-machine,
which when driven at great speed by powerful steam or water engines,
produces the electricity in great quantity at some central station.
From this centre the current is conveyed by copper wires laid under the
streets or over the roofs of the houses, these conductors being tapped
of their electric fluid by smaller wires which convey the electricity
into the houses, in a way similar to that in which gas is conveyed by
small pipes from the larger street mains. In each house is an electric
meter, a special invention of Mr. Edison’s, which measures the quantity
of electricity which passes through it. This meter is very ingenious,
and therefore the principle on which it is based may be described. If
a current of electricity be passed through a solution of sulphate of
copper, contained in a copper jar, the sulphate solution is decomposed
and metallic copper is deposited on the inside of the jar. Now it
has been proved by experiment, that the amount of copper deposited
is always directly proportional to the strength and duration of the
electric current. Mr. Edison’s meter consists of such an arrangement,
and he finds that by weighing the copper jar, so as to determine
exactly what it has gained in weight through the metallic deposition
of the solution it contains, he can accurately calculate in units the
amount of electricity that has passed through the meter. By means of
this beautiful discovery electricity can be supplied and paid for in a
manner very similar to that employed in the case of gas at the present
time.
Within the building to be illuminated, the electric fluid reaches the
lamps along small copper wires, about the thickness of ordinary bell
wire, which are covered with a coating of gutta percha to prevent the
escape of the electricity, which might cause sparks or even fire, or in
any case seriously injure any one who might come in contact with the
bare metal, by giving him a very violent if not fatal electric shock.
The lamps themselves may be fixed to ordinary gas brackets. Mr. Edison
has designed some special ones, and the light can be turned on and
off, by means of a tap or button, with as great or even still greater
facility than gas.
Mr. Edison has recently established a central station in New York,
from which he proposes to light the houses included in an area of a
wide radius from the center. In part of this area the installation of
the lamps and wires is now complete, and the light is giving every
satisfaction, the cost being considerably below that of gas, which
in the United States is very expensive. It must be remembered that
electric lighting is comparatively a new science, and not yet fully
understood. There is very little doubt that, by practice, it will
before long approach more nearly to perfection, and sooner or later
entirely supersede gas, the arc form of lamp being employed for the
illumination of streets and large areas, while the incandescent pattern
meets domestic requirements.—_Good Words._