Cost of 1000 candles per hour.s.d.ElectricityIncandescent12Arc03-3/4Coal-gasFlat flame16Incandescent02-1/4Incandescent high pressure01-3/4OilLamp (oil at 8d. per gall.)07-1/4Incandescent lamp02-1/4Kitson lamp01
Petroleum, therefore, at present comes in a very good first in England.
The system that we have noticed at some length has been adapted for lighthouse use, as it gives a light peculiarly fog-piercing. It is said to approximate most closely to ordinary sunlight, and on that account has been found very useful for the taking of photographs at night-time. The portability of the apparatus makes it popular with contractors; and the fact that its installation requires no tearing up of thestreets is a great recommendation with the long-suffering public of some of our large towns.
Another very powerful light is produced by burning the gas given off by carbide of calcium when immersed in water.Acetylenegas, as it is called, is now widely used in cycle and motor lamps, which emit a shaft of light sometimes painfully dazzling to those who have to face it. In Germany the gas is largely employed in village streets; and in this country it is gaining ground as an illuminant of country houses, being easy to manufacture—in small gasometers of a few cubic yards capacity—and economical to burn.
Well supplied as we are with lights, we find, nevertheless, that savants are constantly in pursuit of anidealilluminant.
From the sun are borne to us through the ether light waves, heat waves, magnetic waves, and other waves of which we have as yet but a dim perception. The waves are commingled, and we are unable to separate them absolutely. And as soon as we try to copy the sun’s effects as a source of heat or light we find the same difficulty. The fire that cooks our food gives off a quantity of useless light-waves; the oil-lamp that brightens one’s rooms gives off a quantity of useless, often obnoxious, heat.
The ideal illuminant and the ideal heating agent must be one in which the required waves are in a great majority. Unfortunately, even with our mostperfected methods, the production of light is accompanied by the exertion of a disproportionate amount of wasted energy. In the ordinary incandescent lamp, to take an instance, only 5 or 6 per cent. of the energy put into it as electricity results in light. The rest is dispelled in overcoming the resistance of the filament and agitating the few air-molecules in the bulb. To this we must add the fact that the current itself represents but a fraction of the power exerted to produce it. The following words of Professor Lodge are to the point on this subject:—
“Look at the furnaces and boilers of a steam-engine driving a group of dynamos, and estimate the energy expended; and then look at the incandescent filaments of the lamps excited by them, and estimate how much of their radiated energy is of real service to the eye. It will be as the energy of a pitch-pipe to an entire orchestra.
“It is not too much to say that a boy turning a handle could, if his energy were properly directed, produce quite as much real light as is produced by all this mass of mechanism and consumption of material.”[6]
[6]Professor Oliver Lodge, in a lecture to the Ashmolean Society, 3rd June 1889.
[6]Professor Oliver Lodge, in a lecture to the Ashmolean Society, 3rd June 1889.
The most perfect light in nature is probably that of the glow-worm and firefly—a phosphorescent or “cold” light, illuminating without combustion owing to the absence of all waves but those of the requisitefrequency. The task before mankind is to imitate the glow-worm in the production of isolated light-waves.
The nearest approach to its achievement has occurred in the laboratories of Mr. Nikola Tesla, the famous electrician. By means of a special oscillator, invented by himself, he has succeeded in throwing the ether particles into such an intense state of vibration that they become luminous. In other words, he has created vibrations of the enormous rapidity of light, and this without the creation of heat waves to any appreciable extent.
An incandescent lamp, mounted on a powerful coil, is litwithoutcontact by ether waves transmitted from a cable running round the laboratory, or bulbs and tubes containing highly rarefied gases are placed between two large plate-terminals arranged on the end walls. As soon as the bulbs are held in the path of the currents passing through the ether from plate to plate they become incandescent, shining with a light which, though weak, is sufficiently strong to take photographs by with a long exposure. Tesla has also invented what he calls a “sanitary” light, as he claims for it the germ-killing properties of sunshine. The lamps are glass tubes several feet long, bent into spirals or other convolutions, and filled before sealing with a certain gas. The ends of the glass tube are coated with metal and provided with hooks to connect the lamp with an electric current. The gas becomesluminousunder the influence ofcurrent, but not strictly incandescent, as there is very little heat engendered. This means economy in use. The lamps are said to be cheaply manufactured, but as yet they are not “on the market.” We shall hear more of them in the near future, which will probably witness no more interesting development than that of lighting.
Before closing this chapter a few words may be said about new heating methods. Gas stoves are becoming increasingly popular by reason of the ease with which they can be put in action and made to maintain an even temperature. But the most up-to-date heating apparatus is undoubtedly electrical. Utensils of all sorts are fitted with very thin heating strips (formed by the deposition of precious metals, such as gold, platinum, &c., on exceedingly thin mica sheets), through which are passed powerful currents from the mains. The resistance of the strip converts the electromotive energy of the current into heat, which is either radiated into the air or into water for cookery, &c.
In all parts of the house the electric current may be made to do work besides that of lighting. It warms the passages by means of special radiators—replacing the clumsy coal and “stuffy” gas stove; in the kitchen it boils, stews, and fries, heats the flat-irons and ovens; in the breakfast room boils the kettle, keeps the dishes, teapots, and coffee-pots warm; in the bathroom heats the water; in the smoking-room replaces matches; inthe bedroom electrifies footwarmers, and—last wonder of all—even makes possible an artificially warm bed-quilt to heat the chilled limbs of invalids!
The great advantage of electric heating is the freedom from all smell and smoke that accompanies it. But until current can be provided at cheaper rates than prevail at present, its employment will be chiefly restricted to the houses of the wealthy or to large establishments, such as hotels, where it can be used on a sufficient scale to be comparatively economical.
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