there is something bewildering in the recent rush of constructive
talent into this domain of applied electricity. The question and its
prospects are modified from day to day, a steady advance being made
towards the improvement both of machines and regulators. With regard
to our public lighting, I strongly lean to the opinion that the
electric light will at no distant day triumph over gas. I am not so
sure that it will do so in our private houses. As, however, I am
anxious to avoid dropping a word here that could influence the share
market in the slightest degree, I limit myself to this general
statement of opinion.
To one inventor in particular belongs the honour of the idea, and the
realisation of the idea, of causing the carbon rods to burn away like
a candle. It is needless to say that I here refer to the young
Russian officer, M. Jablochkoff. He sets two carbon rods upright at a
small distance apart, and fills the space between them with an
insulating substance like plaster of Paris. The carbon rods are fixed
in metallic holders. A momentary contact is established between the
two carbons by a little cross-piece of the same substance placed
horizontally from top to top. This cross-piece is immediately
dissipated or removed by the current, the passage of which once
established is afterwards maintained. The carbons gradually waste,
while the substance between them melts like the wax of a candle. The
comparison, however, only holds good for the act of melting; for, as
regards the current, the insulating plaster is practically inert.
Indeed, as proved by M. Rapieff and Mr. Wilde, the plaster may be
dispensed with altogether, the current passing from point to point
between the naked carbons. M. de Méritens has recently brought out a
new candle, in which the plaster is abandoned, while between the two
principal carbons is placed a third insulated rod of the same
material. With the small de Méritens machine two of these candles can
be lighted before you; they produce a very brilliant light. [Footnote:
The machine of M. de Méritens and the Farmer-Wallace machine were
worked by an excellent gas-engine, lent for the occasion by the
Messrs. Crossley, of Manchester. The Siemens machine was worked by
steam.] In the Jablochkoff candle it is necessary that the carbons
should be consumed at the same rate. Hence the necessity for
alternating currents by which this equal consumption is secured. It
will be seen that M. Jablochkoff has abolished regulators altogether,
introducing the candle principle in their stead. In my judgment, the
performance of the Jablochkoff candle on the Thames Embankment and the
Holborn Viaduct is highly creditable, notwithstanding a considerable
waste of light towards the sky. The Jablochkoff lamps, it may be
added, would be more effective in a street, where their light would be
scattered abroad by the adjacent houses, than in the positions which
they now occupy in London.
*****
It was my custom some years ago, whenever I needed a new and
complicated instrument, to sit down beside its proposed constructor,
and to talk the matter over with him. The study of the inventor's
mind which this habit opened out was always of the highest interest to
me. I particularly well remember the impression made upon me on such
occasions by the late Mr. Darker, a philosophical instrument maker in
Lambeth. This man's life was a struggle, and the reason of it was not
far to seek. No matter how commercially lucrative the work upon which
he was engaged might be, he would instantly turn aside from it to
seize and realise the ideas of a scientific man. He had an inventor's
power, and an inventor's delight in its exercise. The late Mr. Becker
possessed the same power in a very considerable degree. On the
Continent, Froment, Breguet, Sauerwald, and others might be mentioned
as eminent instances of ability of this kind. Such minds resemble a
liquid on the point of crystallisation. Stirred by a hint, crystals
of constructive thought immediately shoot through them. That Mr.
Edison possesses this intuitive power in no common measure, is proved
by what he has already accomplished. He has the penetration to seize
the relationship of facts and principles, and the art to reduce them
to novel and concrete combinations. Hence, though he has thus far
accomplished nothing that we can recognise as new in relation to the
electric light, an adverse opinion as to his ability to solve the
complicated problem on which he is engaged would be unwarranted.
I will endeavour to illustrate in a simple manner Mr. Edison's alleged
mode of electric illumination, taking advantage of what Ohm has taught
us regarding the laws of the current, and what Joule has taught us
regarding the relation of resistance to the development of light and
heat. From one end of a voltaic battery runs a wire, dividing at a
certain point into two branches, which reunite in a single wire
connected with the other end of the battery. From the positive end of
the battery the current passes first through the single wire to the
point of junction, where it divides itself between the branches
according to a well-known law. If the branches be equally resistant,
the current divides itself equally between them. If one branch be
less resistant than the other, more than half the current will choose
the freer path. The strict law is that the quantity of current is
inversely proportional to the resistance. A clear image of the
process is derived from the deportment of water. When a river meets
an island it divides, passing right and left of the obstacle, and
afterwards reuniting. If the two branch beds be equal in depth,
width, and inclination, the water will divi de itself equally between
them. If they be unequal, the larger quantity of water will flow
through the more open course. And, as in the case of the water we may
have an indefinite number of islands, producing an indefinite
subdivision of the trunk stream, so in the case of electricity we may
have, instead of two branches, any number of branches, the current
dividing itself among them, in accordance with the law which fixes the
relation of flow to resistance.
Let us apply this knowledge. Suppose an insulated copper rod, which
we may call an 'electric main,' to be laid down along one of our
streets, say along the Strand. Let this rod be connected with one end
of a powerful voltaic battery, a good metallic connection being
established between the other end of the battery and the water-pipes
under the street. As long as the electric main continues unconnected
with the water-pipes, the circuit is incomplete and no current will
flow; but if any part of the main, however distant from the battery,
be connected with the adjacent water-pipes, the circuit will be
completed and the current will flow. Supposing our battery to be at
Charing Cross, and our rod of copper to be tapped opposite Somerset
House, a wire can be carried from the rod into the building, and the
current passing through the wire may be subdivided into any number of
subordinate branches, which reunite afterwards and return through the
water-pipes to the battery. The branch currents may be employed to
raise to vivid incandescence a refractory metal like iridium or one of
its alloys. Instead of being tapped at one point, our main may be
tapped at one hundred points. The current will divide in strict
accordance with law, its power to produce light being solely limited
by its strength. The process of division closely resembles the
circulation of the blood; the electric main carrying the outgoing
current representing a great artery, the water-pipes carrying the
return current representing a great vein, while the intermediate
branches represent the various vessels by which the blood is
distributed through the system. This, if I understand aright, is Mr.
Edison's proposed mode of illumination. The electric force is at
hand. Metals sufficiently refractory to bear being raised to vivid
incandescence are also at hand. The principles which regulate the
division of the current and the development of its light and heat are
perfectly well known. There is no room for a 'discovery,' in the
scientific sense of the term, but there is ample room for the exercise
of that mechanical ingenuity which has given us the sewing machine and
so many other useful inventions. Knowing something of the intricacy
of the practical problem, I should certainly prefer seeing it in Mr.
Edison's hands to having it in mine. [Footnote: More than thirty years
ago the radiation from incandescent platinum was admirably
investigated by Dr. Draper of New York.]
*****
It is sometimes stated as a recommendation to the electric light, that
it is light without heat; but to disprove this, it is only necessary
to point to the experiments of Davy, which show that the heat of the
voltaic arc transcends that of any other terrestrial source. The
emission from the carbon points is capable of accurate analysis. To
simplify the subject, we will take the case of a platinum wire at
first slightly warmed by the current, and then gradually raised to a
white heat. When first warmed, the wire sends forth rays which have
no power on the optic nerve. They are what we call invisible rays;
and not until the temperature of the wire has reached nearly 1,000°
Fahr, does it begin to glow with a faint, red light. The rays which
it emits prior to redness are all invisible rays, which can warm the
hand but cannot excite vision. When the temperature of the wire is
raised to whiteness, these dark rays not only persist, but they are
enormously augmented in intensity. They constitute about 95 per cent.
of the total radiation from the white-hot platinum wire. They make up
nearly 90 per cent. of the emission from a brilliant electric light.
You can by no means have the light of the carbons without this
invisible emission as an accompaniment. The visible radiation is, as
it were, built upon the invisible as its necessary foundation.
It is easy to illustrate the growth in intensity of these invisible
rays as the visible ones enter the radiation and augment in power. The
transparency of the elementary gases and metalloids--of oxygen,
hydrogen, nitrogen, chlorine, iodine, bromine, sulphur, phosphorus,
and even of carbon, for the invisible heat rays is extraordinary.
Dissolved in a proper vehicle, iodine cuts the visible radiation
sharply off, but allows the invisible free transmission. By
dissolving iodine in sulphur, Professor Dewar has recently added to
the number of our effectual ray-filters. The mixture may be made as
black as pitch for the visible, while remaining transparent for the
invisible rays. By such filters it is possible to detach the
invisible rays from the total radiation, and to watch their
augmentation as the light increases. Expressing the radiation from a
platinum wire when it first feels warm to the touch--when, therefore,
all its rays are invisible--by the number 1, the invisible radiation
from the same wire raised to a white heat may be 500 or more.
[Footnote: See article 'Radiation', vol. i.]
It is not, then, by the diminution or transformation of the
non-luminous emission that we obtain the luminous; the heat rays
maintain their ground as the necessary antecedents and companions of
the light rays. When detached and concentrated, these powerful heat
rays can produce all the effects ascribed to the mirrors of Archimedes
at the siege of Syracuse. While incompetent to produce the faintest
glimmer of light, or to affect the most delicate air-thermometer, they
will inflame paper, burn up wood, and even ignite combustible metals.
When they impinge upon a metal refractory enough to bear their shock
without fusion, they can raise it to a heat so white and luminous as
to yield, when analysed, all the colours of the spectrum. In this way
the dark rays emitted by the incandescent carbons are converted into
light rays of all colours. Still, so powerless are these invisible
rays to excite vision, that the eye has been placed at a focus
competent to raise platinum foil to bright redness, without
experiencing any visual impression. Light for light, no doubt, the
amount of heat imparted by the incandescent carbons to the air is far
less than that imparted by gas flames. It is less, because of the
smaller size of the carbons, and of the comparative smallness of the
quantity of fuel consumed in a given time. It is also less because
the air cannot penetrate the carbons as it penetrates a flame. The
temperature of the flame is lowered by the admixture of a gas which
constitutes four-fifths of our atmosphere, and which, while it
appropriates and diffuses the heat, does not aid in the combustion;
and this lowering of the temperature by the inert atmospheric
nitrogen, renders necessary the combustion of a greater amount of gas
to produce the necessary light. In fact, though the statement may
appear paradoxical, it is entirely because of its enormous actual
temperature that the electric light seems so cool. It is this
temperature that renders the proportion of luminous to non-luminous
heat greater in the electric light than in our brightest flames. The
electric light, moreover, requires no air to sustain it. It glows in
the most perfect air vacuum. Its light and heat are therefore not
purchased at the expense of the vitalising constituent of the
atmosphere.
Two orders of minds have been implicated in the development of this
subject; first, the investigator and discoverer, whose object is,
purely scientific, and who cares little for practical ends; secondly,
the practical mechanician, whose object is mainly industrial. It
would be easy, and probably in many cases true, to say that the one
wants to gain knowledge, while the other wishes to make money; but I
am persuaded that the mechanician not unfrequently merges the hope of
profit in the love of his work. Members of each of these classes are
sometimes scornful towards those of the other. There is, for example,
something superb in the disdain with which Cuvier hands over the
discoveries of pure science to those who apply them: 'Your grand
practical achievements are only the easy application of truths not
sought with a practical intent--truths which their discoverers pursued
for their own sake, impelled solely by an ardour for knowledge. Those
who turned them into practice could not have discovered them, while
those who discovered them had neither the time nor the inclination to
pursue them to a practical result. Your rising workshops, your
peopled colonies, your vessels which furrow the seas; this abundance,
this luxury, this tumult,'--this commotion,' he would have added, were
he now alive, 'regarding the electric light'--'all come from
discoverers in Science, though all remain strange to them. The day
that a discovery enters the market they abandon it; it concerns them
no more.'
In writing thus, Cuvier probably did not sufficiently take into
account the reaction of the applications of science upon science
itself. The improvement of an old instrument or the invention of a
new one is often tantamount to an enlargement and refinement of the
senses of the scientific investigator. Beyond this, the amelioration
of the community is also an object worthy of the best efforts of the
human brain. Still, assuredly it is well and wise for a nation to
bear in mind that those practical applications which strike the public
eye, and excite public admiration, are the outgrowth of long
antecedent labours begun, continued, and ended, under the operation of
a purely intellectual stimulus. 'Few,' says Pasteur, 'seem to
comprehend the real origin of the marvels of industry and the wealth
of nations. I need no other proof of this than the frequent
employment in lectures, speeches, and official language of the
erroneous expression, "applied science." A statesman of the greatest
talent stated some time ago that in our day the reign of theoretic
science had rightly yielded place to that of applied science. Nothing,
I venture to say, could be more dangerous, even to practical life,
than the consequences which might flow from these words. They show
the imperious necessity of a reform in our higher education. There
exists no category of sciences to which the name of "applied science"
could be given. We have science and the applications of science which
are united as tree and fruit.'
*****
A final reflection is here suggested. We have amongst us a small
cohort of social regenerators--men of high thoughts and
aspirations--who would place the operations of the scientific mind
under the control of a hierarchy which should dictate to the man of
science the course that he ought to pursue. How this hierarchy is to
get its wisdom they do not explain. They decry and denounce
scientific theories; they scorn all reference to aether, and atoms,
and molecules, as subjects lying far apart from the world's needs; and
yet such ultra-sensible conceptions are often the spur to the greatest
discoveries. The source, in fact, from which the true natural
philosopher derives inspiration and unifying power is essentially
ideal. Faraday lived in this ideal world. Nearly half a century ago,
when he first obtained a spark from the magnet, an Oxford don
expressed regret that such a discovery should have been made, as it
placed a new and facile implement in the hands of the incendiary. To
regret, a Comtist hierarchy would have probably added repression,
sending Faraday back to his bookbinder's bench as a more dignified and
practical sphere of action than peddling with a magnet. And yet it is
Faraday's spark which now shines upon our coasts, and promises to
illuminate our streets, halls, quays, squares, warehouses, and,
perhaps at no distant day, our homes.
THE END.
LONDON: PRINTED BY
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End of Project Gutenberg's Fragments of science, V. 1-2, by John Tyndall