This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
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.
A recent address before the New York Electric Light Association.