Popular Science Monthly/Volume 5/October 1874/The Electric Light for Steamships
|THE ELECTRIC LIGHT FOR STEAMSHIPS.
By JOHN TROWBRIDGE,
ASSISTANT PROFESSOR OF PHYSICS AT HARVARD UNIVERSITY.
THE employment of the electric light for general purposes of illumination has not, hitherto, been successful. The difficulty of maintaining it constant, and the expense attending its use, have prevented its employment. In the old method of producing the light by a great number of cells, the chief difficulties arose in keeping the strength of the current constant, and in regulating the distance of the carbon-points between which the light was produced. Certain forms of the Daniell cell, notably that constructed by Sir William Thomson ("Jenkins's Electricity," p. 223), give a sensibly constant current for an indefinite period, if watched with great care. The solutions of the cells, however, need to be carefully removed from time to time. The distance of the carbon-points also can be regulated by various contrivances, which do the work required of them in an admirable manner. Still, chemical action cannot be looked to as an economical and constant source of the electric light.
The remarkable improvements in magneto-electric engines have led to another source of the electric light, and seem to afford a better solution of the problem of its economical use. The principle which underlies all magneto-electric engines can be briefly stated thus: The movement of an electro-magnet in the neighborhood of a stationary magnet, which may also be an electro-magnet, is sufficient to induce a current in the coil of the first electro-magnet, and this current can be exalted in strength almost indefinitely by its proper direction, and by the rapidity of the mechanical movement. The most noted engines are those of Siemen and Hulske, Wild, Ladd, and the Gramme machine. Some idea of the power of these engines can be gained from the following statement in regard to a Wild machine, of a size intended to be used for the production of the electric light for light-houses: "When worked with a power of three horses, it will consume carbon-sticks three-eighths of an inch square, and evolve a light of surpassing brilliancy. With a machine that consumes carbons half an inch square, a light of such intensity is got, that, when put on a lofty building, it casts shadows from the flames of the street-lamps a quarter of a mile distant upon the neighboring walls. The same light, at two feet from the reflector, darkened ordinary sensitized photographic paper as much in twenty seconds as the direct rays of the sun at noon on a clear day in March in one minute" (Ferguson's "Electricity"). With a ten-inch quantity armature, Mr. Wild succeeded in melting an iron rod fifteen inches long and one-quarter inch thick. The entire machine by which this was accomplished was under five feet in length and height, was only twenty inches wide, and weighed a ton and a half. The Ladd engine dispenses with the use of permanent steel magnets, and is a more compact form of the machine than Wild's. The Gramme machine returns again to the use of powerful steel magnets, between the poles of which revolves a ring-shaped electro-magnet. The problem of producing the best machine for the production of electricity by mechanical power is not yet solved. The machines now before the public will doubtless be very much improved. At present, however, the means to attain the sought-for ends seem to be limited. There are not many combinations which can be made. A field of magnetic force being given, the question arises. What is the most economical means of cutting the greatest number of lines of force of the greatest intensity in the unit of time? With the most improved forms of the magneto-electric machine, we are, however, in a condition to produce an electric light of a reasonable degree of constancy and cheapness. If it is a desideratum that steamships should be provided with more powerful lights than those now in use, the electric light is the one to which attention is naturally directed. The first points to be considered are in relation to its cost, its constancy, and readiness of adjustment, and its efficiency in penetrating fogs. The light-house service of Great Britain and France affords the only experience on these points.
The electric light has been tried by Great Britain at Dungeness, and by the French Government at La Hève. The source of the light in both instances was a magneto-electric machine. A force of one and a quarter horse-power was required to drive the British machine, and one and a half the French. The descriptions of these machines show that they were extremely bulky, compared with the more improved forms, like Ladd's and the Gramme machine. The observations on the lights at La Hève are especially interesting, because they afforded a means of comparison between the fog-penetrating power of the electric light and the ordinary oil-light of light-houses. There were two light-houses at La Hève, one of which was provided with an electric light, and the other with an oil-light. The electric light was equivalent to 3,500 Carcel-burners. The oil-light had an intensity of 630 Carcel-burners.
"In foggy weather, in the hundred times of observation, the electric light was seen twice as often as the oil-light, or more. When the intensity of the electric light, compared with that of the oil-lamp with which it was measured, is considered, this is not a favorable exhibit. An advantage, nevertheless, which the electric light very distinctly possessed over the other, was in its creating a kind of glow in the fog, by which mariners were enabled to recognize the position of the capes even when both lights were invisible. Experiments were made with the view of ascertaining, with some approach to accuracy, the relative fog-penetrating power of the two descriptions of light produced by electricity and by ordinary combustion, when the photometric intensities are equal; and also the excess of intensity which must be given to the former light, in order that its power in this respect may be equal to that of a lamp fed by oil. In these experiments it was attempted to imitate, as nearly as possible, the absorbent effect of fogs, by interposing glasses of different colors—red, orange, yellow, etc.—before each of the lights successively. The conclusion which these experiments seem to justify is, that, whenever an electric light exceeds in intensity a light produced by a lamp two and a half times, it will penetrate, at least as well as the latter, the fogs most unfavorable to the transmission of the rays. And, as a fact, in whatever state of the weather, the electric light at La Hève has always had the largest range of visibility" ("Reports of the United States Commissioners to the Paris Exposition, 1867," vol. iii.).
M. Becquerel, in an article on electrical apparatus exhibited in the Exposition of 1862, enters into a calculation of the cost of the electric light, compared with other methods of illumination. His estimates are based upon a light produced by a magneto-electric engine, driven by an engine of two horse-power, which light he calculated was equivalent to that produced by 700 stearine-candles. He compares the light thus obtained with that obtained of equal intensity from the galvanic battery—from coal-gas, oil of colza, tallow, stearine, and wax. "The price of gas taken was 30 of a franc per cubic metre—equivalent to 17 cents per 100 cubic feet; oil of colza, $1.28 per gallon; tallow, in the form of candles, 16 cents; stearine, 36 cents; and wax, 52 cents per pound." The cost of the electric light he assumes to be only that of the combustibles required to run the engine. From these data he deduces the following values:
A light equal to that of 700 stearine-candles will cost per hour:
|produced by the
|to 4 cents,
|to 94 cents.
|Pure oil of Colza
"In point of cheapness there would seem to be no comparison between the electric light and that produced by even the least costly of the materials ordinarily employed for purposes of illumination. Actual experiment, however, in the use of these machines in French lighthouses, has shown that these figures require important modifications" ("United States Commissioner's Report to the Paris Exposition, 1867," vol. iii., p. 421).
The French Commission, in view of the experience gained by the establishment of the light at La Hève, did not advocate the extension of the use of the electric light to light-house illumination in general. The expense of maintaining the electric light at Dungeness, irrespective of the original cost, was estimated to be £758 18s. 9d. per annum. M. Becquerel evidently did not take into account in his calculation the original cost of the machine; and the expense of the light at Dungeness would be modified by the greater cheapness of the more improved forms of engines.
For several years it has been rumored that various steamships were to be furnished with the electric light instead of the old well-established masthead-light. No trial has yet been made. The cost of the apparatus, together with the imperfect means hitherto devised for maintaining the light constant, has deterred, apparently, the owners of steamship lines from making a change in this direction. When we reflect that the best masthead-light now in use can be seen only from four to five miles—by some authorities stated from three to four—and in a fog at night is practically not visible more than the length of a steamship ahead, it is not surprising that the general public look earnestly for a change for the better. The experience which the use of the electric light in light-houses has given us is, on the whole, favorable to an extension of the use of the light to steamships. There is no question of the superiority of the electric light over other powerful lights available for steamships, when the great intensity of the light and the compactness of the necessary apparatus are considered. The following is an estimate of the probable cost of fitting steamships with an electric light, together with its maintenance:
|Regulators and attachments
|Small engine to run the machine
|Interest on capital, at ten per cent
|Salary of electrical engineer
|Carbons (or other incandescent material), repairs, etc.
Suppose that the vessel made 18 trips during the year, of 12 days each (216 days), suppose that the electric light was used 10 hours each night (2,160 hours), giving about 53 cents as the cost per hour, the additional fuel required, estimated at three cents per hour, would bring the estimate up to 56 cents per hour. It is probable that a suitable magneto-electric engine would cost less than our estimate. The engine of Mr. M. G. Farmer, of Boston, the celebrated electrician, bids fair to play an important part in applications of the electric light. The engines of the ship could doubtless run by suitable attachments the magneto-electric engine, and our estimate of one attendant would doubtless prove sufficient, with the aid of the ordinary ship-watch.
When one reflects upon the number of steamships crossing the Atlantic, and the increasing danger of collision, with the feeble lights now in use, one is forced to wonder at the want of agitation of the subject. It is safe to affirm that, had the Ville du Havre been provided with more powerful lights, the fatal collision would not have happened. The loss which the steamship company suffered by this collision would have furnished their entire fleet with the apparatus for producing the electric light. With a careful watch, a light which can be seen three miles on a clear night would doubtless prove sufficient. The fog-whistle, with an equally careful watch, can also be made efficient to prevent collisions. But a careful watch cannot always be had; there are many temptations to be careless. Drowsiness, in chilly weather, creeps upon even a conscientious lookout, and a powerful masthead-light would supplement human fallibility.