I shall experience one difficulty in addressing you this evening,
which is, that although I do not wish to take up your time with purely
elementary matter, I wish to make the subject clear to those who may
not be familiar with its earlier struggles.
If we begin at the beginning we have to go back to the time when
Faraday made the discovery that light could be produced by the
separation of two carbon rods conducting a current of considerable
tension. That is the historical point when electric lighting first
loomed up as a giant possibility of the near future. This occurred
about the year 1846. In some experiments he found that although the
circuit could not be interrupted by any considerable interval when
metallic terminals were used without breaking the current, when carbon
was substituted the interval could be largely increased, and a light
of dazzling brilliancy appeared between the points.
This remarkable effect appears to be produced by the rarefaction of
the air, due to the great heat evolved by the combustion of the
carbon, and also to the passage of incandescent particles of carbon
from pole to pole, thus reducing the resistance, otherwise too great
for the current tension.
That was the beginning of electric lighting; and perhaps it will be
well to bridge the long and comparatively uninteresting interval which
elapsed between this discovery and the equally important one which
alone gave it commercial value--I refer to the production of suitable
currents by mechanical means. That is to say, the substitution of
energy obtained from coal in the form of steam power reduced the cost
to a fraction of what it necessarily was when the galvanic elements
were used. Here is the point; the cost of zinc today is something over
fifty times that of coal, while its energy as a vitalizing agent is
only about five times greater, leaving a very large margin in favor of
the "black diamonds." This is not the only advantage, for the
resulting impulse in the case of mechanical production is much more
uniform in action, and therefore better suited to the end in view,
while the amount of adjustment and attention required is beyond
comparison in favor of the latter means.
The machines adopted were of the magneto variety, and many ingenious
machines of this class were operated with more or less success, being,
however, quickly abandoned upon the introduction of the
dynamo-machine, which gave currents of much greater electromotive
force from the same amount of material, the advantage being chiefly
due to the large increase of magnetic intensity in the field magnets.
At this period lights of enormous power were produced with ease and by
the use of costly lamps. With complicated mechanism a new era in
artificial illumination seemed close at hand, but a grave difficulty
stood in the way--namely, the proper distribution or subdivision of
the light. It was quickly found that the electric difficulty of
subdividing the light, added to the great cost of the lamps then made,
was an apparently insurmountable obstacle to its general adoption, and
the electric light was gradually taking its place as a brilliant
scientific toy, when the world was startled by the introduction of the
Jablochkoff candle, which may fairly claim to have given a greater
impetus to the new light than any previous invention, a stimulus
without which it is even probable that electric lighting might have
slumbered for another decade.
The Jablochkoff candle embodies a very beautiful philosophical
principle, and though its promises have not been fulfilled in general
practice, we must not forget that we owe it much for arousing
scientific men from a dangerous lethargy.
Up to this time the light had always been produced by approximation of
carbon rods with their axes in the same plane; but the Jablochkoff
candle consisted of like rods arranged parallel to each other and
about one-eighth of an inch apart, the intervening space being filled
with plaster of Paris, and the interval at the top bridged by a
conducting medium. The object of the plaster, which is a fairly good
insulating material at ordinary temperatures, is to prevent the
passage of the current except at the top, where the conducting
material just referred to assisted the formation of the arc at that
point, and the resulting intense heat maintained the plaster in a
moderately conducting state until the whole carbon was consumed. Here,
then, was literally an electric "candle," which could be operated
without the costly and unsteady lamps, and fortunately its birthplace
was Paris--then the center of philosophical research; from that period
the future of electric lighting was assured.
When we reflect that owing to the greater disruptive energy of the
positive terminal, the carbon so connected to an ordinary dynamo
machine is consumed very much faster than the negative--sometimes in
the ratio of 3 to 1--it will be clear that some other means of
consuming the Jablochkoff candle had to be used, since the arc would
cease to exist in a very short time by reason of the unequal
consumption of the carbons, and the subsequent increase of the
intervening space beyond the limit of the current tension.
This difficulty M. Gramme overcame with characteristic ingenuity by
adding to the ordinary system a "distributer" capable of delivering
plus and minus currents alternately, thus equalizing the consumption,
besides being able to supply a large number of candles on the multiple
circuit system, each circuit supporting four or five lamps. Thus it
will be seen that a result was attained which at least gave such men
as Siemens, Gramme, and their peers, if such there be, confidence in
the future and a courage which quickly placed the new science safely
beyond the limits of the laboratory. I will not occupy your time by
stating the apparent reasons why the Jablochkoff candle has not fully
sustained its brilliant promise--it will, perhaps, be sufficient to
state that it is now superseded practically, though it must always
occupy an honorable place in scientific annals.
Let us now for a few moments consider what the electric light really
accomplished at about this period, I mean from an economical
standpoint. It appears from some data furnished by an engineer
commissioned by the French Government that the machines were then
capable of maintaining a light equal to from 220 to 450 candles,
measured by comparison with the Carcel burner, per horse power
absorbed--a very good showing considering the youth of the discovery,
but presenting rather a gloomy aspect when we consider that according
to Joule's mechanical equivalent of heat, which is 772 foot pounds, or
the power required to raise one pound of water one degree--and for
lack of anything better, we are obliged to accept that at this
moment--the whole force contained in one pound of coal would maintain
a light equal to 13,000 candles for one hour! That is the ultimate
force, and what we are now able to accomplish is but a small fraction
of this amount.
Unfortunately we are but common mortals, and cannot, like Mr. Keely,
lightly throw off the trammels of natural law; we must, therefore,
endeavor to close this gap by patient study and experiment.
The limited time at my disposal, and a keen consideration for your
feelings, will not permit me to follow the long series of struggles
between mind and matter immediately following Jablochkoff's brilliant
invention; suffice it to say, that the few years just passed have
yielded beyond comparison the most marvelous results in the scientific
history of the world, and it will be superfluous to remind you that a
great part of this has undoubtedly been due to the researches made in
an effort to reduce electric lighting to a commercial basis. To say
that this has been fully accomplished is but to repeat a well known
fact; and in proof of this I quote a high scientific authority by
stating that a result so high as 4,000 candles evolved for 40,000
foot-pounds absorbed has recently been obtained--an efficiency six or
seven times greater than the record of six years ago. In accepting
this statement we must not lose sight of the extreme probability that
such effects were evolved under conditions rarely if ever found in
common practice. Of course, I now refer to the arc system. The volume
of light so generated is incomparably greater than by any other known
method, though in subdivision the limit is sooner reached.
Mr. Hawkesworth--Let me ask you a question, please. Supposing that it
required a one-horse power to produce an arc light of, say, 2,000
candles, would it be possible to produce ten arc lights of 200 candles
each?
Mr. Daft--No, sir; I will tell you why. It would, if no other element
than the simple resistance of the arcs opposed the passage of a
current; then a machine that would produce an inch arc in one light,
if placed on a circuit of sixteen lamps would give to each an arc
one-sixteenth of an inch long naturally; but another difficulty here
presents itself in the shape of a resisting impulse of considerable
electromotive force in the opposite direction, apparently caused by
the intense polarity of the two terminals. The resistance of the arc
itself varies much according to the volume of current used being
usually small with a large quantity of current, and greater with a
current of tension; but this opposing element is always found, and
appears to be the only real obstacle in the way of infinite
subdivision.
Almost every objection which human ingenuity could suggest has been
urged against lighting by electricity, but fortunately electricians
have been able in most cases either to meet the difficulty or prove it
groundless.
In this connection I am led to speak of the common idea that electric
light is injurious to the eyes, first, because of its unsteady
character, and secondly, by reason of the great excess of the more
refrangible rays. Both objections undoubtedly hold good where the
alleged causes exist; but we can now show you a light which is
certainly as steady as the ordinary gaslight--indeed more steady in an
apartment where even feeble currents of air circulate; and I am sure
you will readily acknowledge that the latter objection is disposed of
when I assure you that our light presents the only example with which
I am acquainted of an exact artificial reproduction of the solar
light, as shown by decomposition. The two spectra, placed side by
side, show in the most conclusive manner the identity in composition
of our light with that of the sun.
The remarkable coolness of the electric light, as compared with its
volume by gas, is also due in a great measure to the conspicuous
absence of that large excess of less refrangible, or heat-radiating
principle, which distinguishes almost equally all other modes of
artificial illumination. After the foregoing statement it may seem a
paradox to claim that the electric arc develops the greatest heat with
which we have yet had to deal, but this is so; and the heat has an
intensity quite beyond the reach of accurate measurement by any
instrument now known--it has been variously estimated anywhere between
5,000° and 50,000° F. It is sufficient for our present purpose to know
that the most refractory substances quickly disappear when brought
under its influence--even the imperial diamond must succumb in a short
time. In order to reconcile this fact with its coolness as an
illuminating agent, we have to take into consideration the extreme
smallness of the point from which the light radiates in the electric
arc. A light having the power of many thousand candles will expose but
a fraction of the surface for heat radiation which is shown by one
gas-jet, and, as I have endeavored to explain, these rays contain very
much less of the heating principle than those from gas or other
artificial light.
The purity of electric light has another important aspect, which can
scarcely be overestimated--namely, the facility with which all the
most delicate shades of color can be distinguished. I understand from
persons better skilled than myself in such matters that this can be
done almost as readily by electric as by day light, and I have little
doubt that the slight difference in this respect will entirely
disappear when people become somewhat more familiar with the different
conditions--the effect of such shades viewed by electric light being
more like that with comparatively feeble direct sunlight than the
subdued daylight usually prevailing in stores and warehouses.
Again, it has frequently been urged that persons working by electric
light have thus induced inflammation of the eyes. No doubt this is so
with light containing the highly refrangible rays in excess; but it is
difficult to see how such an effect can occur with light composed as
is the light with which the eyes are constructed to operate in perfect
harmony.
As you are aware, there are other methods of obtaining light by
electric energy, and in order to make a fair comparison of one which
has lately attracted a great deal of attention and capital, I will
relate to you the result of observations made during a recent visit to
the office of an eminent electrician. The light was that known as
incandescent--a filament of carbon raised to a light-emitting heat in
vacuo. The exclusion of the air is necessary to prevent the otherwise
rapid destruction of the carbon by combination with oxygen. At the
time of my visit there were 62 lamps in circuit. According to their
statement each lamp was of 16-candle power--I accept their statement
as correct; this will give us an aggregate of 992 candles. The
generator was vitalized by an engine rated by the attendants in charge
at 6-horse power. I found that it was a 5×7 cylinder, working with
very little expansion 430 revolutions per minute, with 90 pounds of
live steam, in a boiler not 15 feet from the engine. I have every
reason to believe that the steam was delivered at the cylinder with an
almost inappreciable loss on 90 pounds. Under those conditions I think
it is perfectly fair to assume (you have the data, so that you can
calculate it afterwards) that 750,000 foot pounds were consumed in
producing those 60 lights, aggregating 992 candles. In the kind of
engine they had, 750,000 foot pounds requires a consumption of about
100 pounds of coal per hour. It was an ordinary high speed engine.
That 750,000 foot pounds, I assume, required 100 pounds of coal. That
is the only weak point in my data; I do not know that to be true; but
I never saw an engine of that form yet capable of delivering 1-horse
power with less consumption than four to five pounds of coal per horse
power per hour. I want to be as fair as I can in the matter. I wish to
compare this, as they have taken particular pains to compare it, with
gas, at the present cost of gas.
The hundred pounds of coal will produce 400 feet of gas; 400 feet of
gas will evolve the effect of 1,500 candles. So you see the position
we are in. In consuming that coal directly by destructive distillation
you can produce 1,500 candles light; by converting it into power, and
then again into light by incandescence, you produce 992! Expressing
this in other words, we may say that in producing the light from coal
by the incandescent system you lose one-third of the power as compared
with gas, by actually converting the coal into gas, and delivering it
in the ordinary manner. Those are facts. It has been suggested to me
that I am too liberal in my estimate of coal consumed--that those
engines consume more than four or five pounds per horse power per
hour; but I prefer to give them the benefit of the doubt.
Mr. Rothschild--If I understood you correctly, this electric light
costs more than gas?
Mr. Daft--_Must_ do by this system. You cannot do better, so far as
our philosophy goes. But this whole system of illumination, as now
practiced is a financial fallacy.
Mr. Rothschild--That is what Professor Sawyer says.
Mr. Daft--The same amount of energy converted into light by our arc
system will produce 30,000 candles. We are perfectly willing to
demonstrate that at any time. I am free to admit that the minute
subdivision obtained by the Edisonian, Swan, or Fox system--they do
not differ materially--is a great desideratum; but this cannot bridge
the financial gulf.
Mr. Lendrum--Now please state what we have accomplished.
Mr. Daft--Certainly; and in so doing I prefer to give our results as
actually occurring in everyday work; and in this connection let me
remind you that in no branch of physics are the purely experimental
effects so well calculated to deceive, if not fairly conditioned. As
we have seen, it is claimed on excellent authority that the equivalent
of 4,000 candles appeared in an arc by expending 40,000 foot pounds of
energy at the generator, but with everyday conditions it is at present
idle to expect such efficiency. Commercially we can give by our own
system 3,000 candles for 40,000 foot pounds absorbed; this may be done
for an indefinite length of time and leave nothing to be desired on
the score of steadiness. Unfortunately there is no unit of photometric
measurement generally recognized in this country, each electrician
having so far adopted one to suit his own convenience; but in making
the foregoing statement I wish it to be understood that our efficiency
would appear still greater if measured by some of the methods now
employed. For our own satisfaction we have endeavored to be at least
approximately accurate, at the same time wishing to avoid the
affectation of extreme precision, such, for example, as adding twenty
or thirty candles to measurements of so many thousands, and we are
satisfied that the most critical expert tests will prove our claim to
be within the mark. The limit of subdivision is only reached when the
difficulty of further increasing the electromotive force of the
machines, involving great care in insulation and a host of other
troubles arising, so to speak, at very high pressure, is balanced by
the objections to working in multiple arc; this appears to occur now
at something below 40 lights, but will in all probability be greatly
extended within a short time. The machines are so constructed that the
local currents, usually productive of dangerous heating, are turned to
useful account, so that the point where radiation exceeds production
is soon reached, and provided the machines are not speeded beyond the
proper limit, they may be run continuously without the slightest
indication of lost vitality. I need scarcely remind you that this is a
most important feature, and by no means a common one.
The lamps used in our system I believe to be the simplest known form
of regulator; indeed it seems scarcely possible that anything less
complicated could perform the necessary work; as a matter of fact we
may confidently assert that it cannot be made less liable to
derangement. It has frequently been placed on circuit by persons
totally inexperienced in such matters, and still has yielded results
which we are quite willing to quote at any time.
I will not now trespass on your patience further than will enable me
to state that experiments now in hand indicate conclusively that
domestic electric lighting of the immediate future will be
accomplished in a manner more beautiful and wondrous than was ever
shadowed in an Arabian Night's dream. I hesitate somewhat to make
these vague allusions, since so many wild promises, for which I am not
responsible, remain unfulfilled, but the time is surely near at hand
when a single touch will illuminate our homes with a light which will
combine all the elements of beauty, steadiness, softness, and absolute
safety, to a degree as yet undreamed of. I do not ask you to accept
this without question, but only to remember that within the last
decade wires have been taught to convey not only articulate sounds,
but the individual voices you know amidst a thousand, and even light
and heat have each been made the medium of communicating our thoughts
to distant places!
Not the least remarkable phenomenon in this connection is the
intellectual condition of the people who have welcomed these marvelous
achievements and allowed them to enter into their everyday life, thus
removing the greatest barriers of the past and paving the way for that
philosophical millennium inevitably awaiting those who may be
fortunate enough to survive the next decade.
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