The Electric Light is the brightest meteor that has flashed across the
horizon of promise during the present century. When first exhibited
as a means of illumination, about twelve years ago, the splendour of
the rays emitted, and the delusive representations of the small cost
required to produce such a brilliant light, led the public to believe
that the career of gas-lighting was drawing to a close, and that night
would be turned into day by this wonderful demonstration of electrical
power. The light produced by charcoal points, subjected to the action
of a powerful voltaic battery, was, however, no novelty at that time;
for as far back as 1810, Sir Humphry Davy was accustomed to exhibit
that development of electrical force at the Royal Institution, and it
formed a standard experiment in most chemical lectures. But it seems
not to have been thought applicable in those days to the purposes of
illumination; and when Mr. Staite brought it into notice, and exhibited
its effects on the tops of some public buildings, it was considered one
of the most wonderful inventions of the age.
Mr. Staite's patent, taken out in 1847, though commonly supposed to
be for the Electric Light generally, was limited in its clauses to
the construction of a voltaic battery and apparatus, adapted for
maintaining constancy, and for giving steadiness to the light. The
merely temporary continuance of the _voltaic arc_, as it was formerly
called, seemed indeed to preclude the possibility of its adoption as a
means of illumination; it was therefore a great point gained to give
stability and constancy to the light. The difficulty of accomplishing
this will be perceived when it is known that the charcoal points,
between which the action takes place, are constantly undergoing change,
the particles of carbon being transferred from one to the other. There
is no actual combustion of the charcoal, in the ordinary meaning of
the term; the action is principally confined to the transfer of the
charcoal connected with the positive pole, to that connected with the
negative pole of the voltaic battery, a hollow being formed in one, and
a pyramidical accumulation of particles in the other. This action was
beautifully shown by Professor Faraday at the Royal Institution last
year, by projecting the image of the charcoal points on to a screen,
by means of the Electric Light itself. The image, magnified by the
lenses of the electric lamp, could thus be distinctly seen without
being too brilliant to dazzle the eyes. The particles of carbon, heated
to whiteness, were perceived to be in active motion, and the piling
up of the pyramid in one, and the hollow produced in the other, were
continually varying the distances between them, and thus tending to
cause unsteadiness in the light.
Numerous contrivances have been adopted for the purpose of keeping
the points at exactly the same distance, as the want of stability was
supposed to be the only obstacle to the adoption of the Electric Light.
These contrivances have so far succeeded, that a tolerably steady light
can be maintained for some time, but under the most careful management
the points occasionally approach too near or are too far apart to
maintain an equable light.
Among other inventions to increase the steadiness of the light is one
that was patented in 1856, by Mr. Way, in which mercury is substituted
for charcoal, but the steadiness of light to be thus acquired must
be attained with a great loss of illuminating power, and the vapour
arising from the combustion of the mercury would be extremely injurious
to health.
Mr. Hearder, of Plymouth, has produced more brilliant effects with the
Electric Light than any other person. Some remarkable exhibitions of
the power of the light were made by him, in April, 1849, from the top
of the Devonport Column, and several scientific gentlemen undertook to
make observations at different localities to a distance of five miles.
At Tremeton Castle, on the banks of the Tamar, a distance of nearly 3½
miles; the light cast a strong shadow, and writing could be distinctly
read by it. The space illuminated was at least three quarters of a
mile broad. To aid the effect, a reflector was employed, and when the
rays were directed to the clouds, they had the appearance of a huge
comet, the reflector being the nucleus. The intensity of the light was
ascertained to be equal to that of 301,400 mould candles of six to the
pound, whilst the light of the Breakwater Lighthouse was equal to only
150 candles. At a distance of five miles the light was sufficiently
powerful to enable persons to read a book.
The battery employed by Mr. Hearder in these brilliant experiments
consisted of 80 cells of a Maynooth battery, 4 inches square, and
the carbon cylinders between which the light appeared were formed of
powdered coke, mixed with tar, and rammed into a tube three quarters
of an inch in diameter. When these cylinders are about a quarter of
an inch apart, the Electric Light appears at the end of each for the
space of more than half an inch. The light, during the experiments at
Plymouth, was maintained for three hours, and the materials employed
amounted to one pound and a-half of zinc, 114 fluid ounces of sulphuric
acid, the same quantity of nitric acid, and six pounds of muriate of
ammonia.[14]
The most serious practical objection to the introduction of the
Electric Light, as a means of general illumination, is its expense.
When the project was first brought into notice, attempts were made to
show that the battery power required might be obtained at little cost,
and in this respect some deceptions were practised not creditable to
the parties engaged in promoting the scheme. It has been proved by Mr.
Grove that the cost of ordinary batteries necessary to maintain the
light in full brilliancy would greatly exceed the price of an equal
light from gas.
A plan was patented for generating the required voltaic power, free
from cost, by applying the residual sulphate of zinc as paint, and an
Electric Power and Light Company was formed to carry out the project.
But the plan failed, and the affairs of the company have recently been
"wound up."
Until some cheaper mode of generating electricity than is at present
known be invented, there is no hope of the Electric Light becoming
generally available, but there are special circumstances in which
it may be applied with advantage. It is peculiarly applicable for
lighthouses, as its rays would penetrate through a foggy atmosphere
that would obscure the light of ordinary flames, and in such cases the
extra cost should not operate as an obstacle to its use.