CURIOSITIES OF THE ELECTRIC LIGHT.
The first curiosity of the electric light was of course its discovery in 1802 by Humphry Davy, then an assistant-lecturer at the Royal Institution. With one of the new batteries which Volta had invented two years before, Davy was surprised to get a brilliant white light when the poles of the battery were joined through two pieces of carbon. Later on, his astonishment was increased when he found how intensely hot was this ‘arch’ of carbon light—the hottest known artificial source. ‘Platinum,’ he wrote, ‘was melted as readily as is wax in the flame of a common candle; quartz, the sapphire, magnesia, lime, all entered into fusion.’ Even the diamond swells out into a black mass in the electric arc, and carbon itself has been known to soften. Dr Siemens, as is well known, utilised this fervent heat to fuse metals in a crucible. With the arc from a dynamo capable of giving a light of five thousand candles, he fused fifteen pounds of broken files in as many minutes. Indeed, the temperature of the arc ranges from two thousand to five thousand degrees Centigrade. Another curiosity of the arc is that it can be shown in water or other liquids without quenching. Liquids have a diffusive action on the light; and a globule of fused oxide of iron between platinum wires conveying the current, produces a very fine golden light. The fused plaster of Paris between the carbons of the Jablochkoff candle also forms a brilliant source of light in the arc; as does the marble separator which answers the same purpose in the lampe soleil. Indeed, this white-hot marble, rendered luminous by the arc, gives out a mellow radiance so closely resembling sunshine as to give the lamp its name. Such a light is very suitable for illuminating picture-galleries.
Electric light is also produced by sending a discharge through vacuum tubes like those of Geissler; and the varied colours thus produced are exceedingly pretty. Phosphorescent substances, too, such as the sulphide of barium, or the platino-barium cyanide, become highly luminous when inclosed in a tube and traversed by the electric current.
Besides the voltaic arc, we have now, however, another kind of electric light—namely, the incandescence which is produced by sending the current through a very slender filament of platinum wire or carbon fibre inclosed in a glass bulb exhausted of air. Such are the lamps of Swan, Edison, and others. These lamps have also their curious features. The temperature of the filament is of course much lower than the temperature of the arc. It is only about eighteen hundred degrees Centigrade, for if it were higher, the delicate filament would be dissipated into vapour which would condense like smoke on the cool glass. With a platinum filament, the metal would ‘silver’ the interior of the bulb. Curiously enough, when the copper ‘electrodes’ or wires conveying the current inside the bulb to the filament of an Edison lamp are accidentally dissipated by excess of current, the carbon thread seems to shelter the glass from the copper shower, for Dr J. Fleming has observed that there is always a blank line on the glass opposite the filament, while all the rest is coated with a film of copper. When the carbon itself is dissipated, this blank line is not seen, and the whole interior of the bulb appears to be smoked. According to Dr Fleming, this means that the molecules of copper move in straight lines in the vacuum.
During the ordinary action of one of these lamps there is believed to be a kind of molecular bombardment between the two sides of the carbon filament, which is usually bent into a loop. This battery of atoms in time disintegrates the filament near its junction with the wires where it is severest, and a patent has recently been taken out by Mr Brush, the well-known inventor, for the insertion of a mica screen between the legs of the filament to shield them from the pellets.
The spectrum of the voltaic arc consists of the continuous ribbon spectrum of the white-hot solid carbons, and certain bright lines due to the glowing vapours of the arc. The light is rich in the blue or actinic rays so productive of chemical action, and hence it is, perhaps, that Dr Siemens found it so effective in forcing fruit and flowers by night in lieu of the sun. It helps the development of chlorophyl; and perhaps the electricity itself has also something to do with assisting growth, apart from the light, for several French experimenters have found that electrified soil and air seem to foster plants better than unelectrified. It is remarkable, too, that young bamboo shoots grow very rapidly after the thunderstorms which usher in the Indian monsoons.
The power of the arc-light is something unrivalled by any other light, whether of limelight or magnesium. At the famous Crystal Palace Electrical Exhibition, an arc reputed to be one hundred and fifty thousand candles in power was lighted every evening. The carbons were stout copper-plated bars nearly two and a half inches thick. This intensity of illumination renders the arc eminently adapted for lighthouses and search-lights. Hence it is that the French government have decided to light forty of their coast lighthouses by electricity, and that most of our warships and military trains are now equipped with electric lamps for searching purposes. We read that the fleet at Alexandria explored the Egyptian forts by night with powerful arcs; and that the French Admiral at Madagascar struck terror into the breasts of the simple Hovas by a similar display.
For scouring the sea in search of torpedo-boats by night, or icebergs and other ships during a fog, the value of the arc-light cannot be too highly estimated. The screw-steamer Faraday, while engaged some time ago in laying a new Atlantic cable, would have run right into an iceberg in a Newfoundland fog, but for the electric beam projected from her bows into the misty air ahead. Fog, however, has a peculiarly strong quenching power over the arc-light, owing to the preference it has for absorbing all the blue rays, and to the comparative poverty of the orange colour. Hence it is that electric arc-lamps look so white and dim in a dense fog. A single gas-jet can be seen about as far as a two-thousand-candle arc-lamp. This is because the gas-jet is rich in those red rays which penetrate a fog without being absorbed; whereas it is poor in the blue rays which are quenched. For this reason, also, the incandescence lamp is preferable to the arc for a misty atmosphere.
The incandescence lamp can also burn under water, and owing to its pretty shape, its pure light, its cleanliness, and independence of everything except wires to bring the current to it, is highly suitable for decorative purposes. It particularly lends itself to ornamental devices of a floral order; and a great variety of chandeliers and brackets have now been designed representing various plants with leaves of brass or filagree, and flowers composed of tinted crystal cups containing the lamps. Fruit is also simulated by lamps of coloured glass. For example, at a Drury Lane Christmas pantomime, both holly and mistletoe berries were imitated by incandescence lamps of crimson and opal glass. Artificial lemon-trees, with fruit consisting of yellow lamps, also make a pretty dining-table ornament. So do vases of roses with incandescence lamps hid in them, an ornament devised by Mr J. W. Swan for his residence at Bromley. Aquaria, too, can be lighted internally by incandescence bulbs, and it would be very pretty to see the lamps lying beside growing sea-anemones, whose expansion might seem the more lovely under the stimulus of their rays.
A Christmas-tree looks very pretty when lighted by a hundred incandescence lamps; the first attempted being in all probability that in the Swedish section of the Electrical Exhibition held in Paris two years ago. At the Vienna Electrical Exhibition there are, while we write, some novel effects of electric illumination; for instance, there is a hall lighted entirely from the ceiling by electricity. The ceiling is painted a deep blue to represent the sky, and studded with innumerable stars in the shape of incandescence lamps. This reminds us of the allegorical sun produced in the window of Mr Mayal, the well-known photographer, by means of the same illuminant.
From its cool brightness and safety from fire, the incandescence light is very well adapted for theatres, and there are now several opera-houses and theatres lighted by it. The Savoy Theatre, London; the Princess’s Theatre, Manchester; the Lyceum Theatre, Edinburgh, &c., are all lit by incandescence lamps owing to its brilliance as compared with gas. Some change was necessary in the making-up of the actors and actresses, and the painting of the scenes; but at the New Grand Theatre, Islington, the changes have been avoided by the use of yellow glass bulbs which soften the light. At the Electrical Exhibition, Vienna, there is a model theatre with numerous scenic effects never before attempted by gas; and moonlight, sunrise, sunset, twilight, and night are all imitated with great fidelity. In the drama of Love and Money at the Adelphi Theatre, a flood of daylight bursting in upon some entombed miners through a hole cut in the coal by a rescuing party was very well imitated by a beam of ‘arc’ light. The practice of wearing tiny star lamps on the hair or dress has also come more into fashion. Probably the first use of it was by the fairies in the comic opera of Iolanthe at the Savoy Theatre. Each fairy carried a small accumulator on her back half concealed by her wings, and this gave electricity to a miniature Swan lamp mounted on her forehead. Ladies are sometimes to be seen with miniature lamps attached to their dresses, and lighted by a touch of their fingers upon a small key hid in their belts. One might have glowworm or firefly ornaments at this rate. The ‘death’s-head’ pin worn by gentlemen in Paris a year or two ago was a similar application of the electric current. On touching a key to complete the electric circuit of a small pocket battery, the eyes of the death’s-head in the wearer’s breast began to shine like sparks of fire.
The use of the electric light for sporting purposes has had some curious developments. Polo, cricket, base ball, skating, and so on, have all been played by night. At the Montreal Ice Carnival last winter, the huge ice palace was illuminated both out and in with thousands of electric lights, and skating, curling, snow-shoeing, and toboganning went on by night as well as day.
Gnats are fascinated by a powerful electric lamp, and dance about it as they do in a beam of evening sunshine. Light has an attraction for many animals besides insects. Flying-fish spring out of the sea when sailors hang a lantern by the ship’s side; and in California now it is the custom to submerge a cluster of Edison lamps from the bows of a boat with a net expanded below. When the fish gather round the light the net is closed on them, and after being hauled out of the water they are put into water-tanks, and sent alive on special cars by overland rail to New York and the Eastern States. The French chasseur also makes a bag sometimes by employing an electric light to attract his feathered game; pigeons especially being lured by it.
Owing to its power, the arc-light is very well suited for signalling purposes; and hence it is now used with the heliograph to signal the approach of cyclones between the British island of Mauritius and Reunion in the Indian Ocean. It has also been proposed to signal by transparent balloons lit by incandescence lamps. The balloon is raised to a good height by a rope which also carries the wires conveying the current to the lamps; and flashes according to an understood code of signals are made by working a key to interrupt the current, as in the act of telegraphing.
Diving operations under the sea are greatly facilitated by the electric light; and a trial was recently made of a powerful lamp at Marseilles in lighting up the hull of a sunken ship. The amber hunters of the Baltic are also using the light for seeking the fossil gum on the sea-bed, instead of waiting until the waves cast it on the shore. Sea-water is remarkably clear, and the rocks of the seashore are often beautifully covered with weeds and shells. It is no wonder, then, that a submarine balloon has been devised by one Signor Toselli at Nice, for going under water to examine them. This observatory holds eight people, and has a glass bottom and an electric light for illuminating the sea-caves.
The electric light is not free from danger; but, from not being explosive, it is far from being as fatal in its effects as gas. There have been several deaths from electric shock caused by the very powerful currents of the Brush and Jablochkoff machines. For instance, a man was killed instantly on board the late Czar’s yacht Livadia when crossing the Bay of Biscay. He had accidentally grasped the bare connections of one of the electric lamps and received the current through his breast. Others have been killed by touching bare wires conveying the current; a man in Kansas City, United States, met his death quite recently in repairing some electric light wires without knowing that the current flowed in them. Carelessness of some kind was the source of these misfortunes; but the use of such very deadly currents is to be deprecated. When the electromotive force of an electric current exceeds five hundred volts it becomes dangerous, and hence it is that the Board of Trade prohibits the use of more powerful currents for general lighting. The use of overhead wires, sometimes uninsulated and never wholly insulated, such as obtains in some parts of the United States, ought also to be eschewed, and underground cables, safe out of harm’s way, employed instead. With cables buried in the earth, we should not have a repetition of the curious incident which recently happened at the Luray Cavern in Virginia, where lightning ran into the cave along the electric light conductors and destroyed some of the finest stalactites.
The plan of having tall masts with a cluster of very powerful lights reflected from the height by mirrors is a very good one, since it obviates the distribution of wires and lamps. By imitating the sun, in this way a Californian town is entirely lighted from one or two masts; and it is satisfactory to know that the system is being tried at South Kensington.
The dynamos of electric machines have been known to explode, or rather burst from the centrifugal force due to the rapid revolution of the armature. An accident of this kind recently caused great alarm in a New York theatre. Sparks from the red-hot carbons of arc-lamps, or between wire and wire of the conductors, have also led to many small fires; but none of any great consequence. A spark is so feeble a source of heat that, unlike the spilling of an oil-lamp, it does not produce a powerful fire, provided the materials it falls among are not highly inflammable. On the whole, the danger of fire with electric lighting, especially incandescence lighting, has probably been exaggerated. The incandescence lamp itself is very safe, since if one be enveloped in light dry muslin and broken, the muslin is not burnt. In fact, the rush of air caused by the broken vacuum entirely dissipates the red-hot filament.
From its injurious aspects we turn now to its beneficial qualities. The arc-light by its brilliance is not good for the eyesight when looked at direct, but there is probably nothing harmful in the light itself, unless it should be the excess of violet rays. It is a cool light; and hot lights, by drying the natural humours of the eye, are the most prejudicial to the sight. The incandescence light which is free from excess of violet rays is also a cool light; and as it neither pollutes nor burns the air of a chamber, it is the best light for a student. Small reading-lamps, fitted with movable arms carrying incandescent bulbs, are now manufactured for this purpose. Even with the incandescence lamp, however, it is advisable not to look at the brilliant filament.
Surgeons and dentists find these little incandescence lamps of great service in examining the teeth and mouth. Some are made no larger than a pea. Others are fitted into silver probes (cooled by circulating water) for insertion into the stomach to illuminate its coats, or enable a physician to diagnose other internal organs. Dr Payne, of Newcastle-on-Tyne, recently made an examination of the liver by inserting one of these endoscopes into it through an incision made in the abdomen. M. Trouvé has also fitted a small lamp to a belt which goes round the physician’s forehead, thereby enabling him to direct the light to where he is looking. Another experimenter has so applied the light that he has been able to photograph the vocal chords while in the act of singing; and a third has illuminated the whole interior of a living fish, so that all the main physiological operations could be witnessed by a class of students. Such services as these could not be rendered by any other known illuminator.