The Romance of Modern Invention Part 22

LIGHTING.

The production of fire by artificial means has been reasonably regarded as the greatest invention in the history of the human race.

Prior to the day when a man was first able to call heat from the substances about him the condition of our ancestors must have been wretched indeed. Raw food was their portion; metals mingled with other matter mocked their efforts to separate them; the cold of winter drove them to the recesses of gloomy caverns, where night reigned perpetual.

The production of fire also, of course, entailed the creation of light, which in its developments has been of an importance second only to the improved methods of heating. So accustomed are we to our candles, our lamps, our gas-jets, our electric lights, that it is hard for us to imagine what an immense effect their sudden and complete removal would have on our existence. At times, when floods, explosions, or other accidents cause a temporary stoppage of the gas or current supply, a town may for a time be plunged into darkness; but this only for a short period, the distress of which can be alleviated by recourse to paraffin lamps, or the more homely candle.

The earliest method of illumination was the rough-and-ready one of kindling a pile of brushwood or logs. The light produced was very uncertain and feeble, but possibly sufficient for the needs of the cave-dweller. With the advance of civilisation arose an increasing necessity for a more steady illuminant, discovered in vegetable oils, burned in lamps of various designs. Lamps have been found in old Egyptian and Etruscan tombs constructed thousands of years ago. These lamps do not differ essentially from those in use to-day, being reservoirs fitted with a channel to carry a wick.

But probably from the difficulty of procuring oil, lamps fell into comparative disuse, or rather were almost unknown, in many countries of Europe as late as the fifteenth century; when the cottage and baronial hall were alike lit by the blazing torch fixed into an iron sconce or bracket on the wall.

The rushlight, consisting of a peeled rush, coated by repeated dipping into a vessel of melted fat, made a feeble effort to dispel the gloom of long winter evenings. This was succeeded by the tallow and more scientifically made wax candle, which last still maintains a certain popularity.

How our grandmothers managed to "keep their eyes" as they worked at st.i.tching by the light of a couple of candles, whose advent was the event of the evening, is now a mystery. To-day we feel aggrieved if our lamps are not of many candle-power, and protest that our sight will be ruined by what one hundred and fifty years ago would have seemed a marvel of illumination. In the case of lighting necessity has been the mother of invention. The tendency of modern life is to turn night into day. We go to bed late and we get up late; this is perhaps foolish, but still we do it. And, what is more, we make increasing use of places, such as bas.e.m.e.nts, underground tunnels, and "tubes," to which the light of heaven cannot penetrate during any of the daily twenty-four hours.

The nineteenth century saw a wonderful advance in the science of illumination. As early as 1804 the famous scientist, Sir Humphrey Davy, discovered the electric arc, presently to be put to such universal use. About the same time gas was first manufactured and led about in pipes. But before electricity for lighting purposes had been rendered sufficiently cheap the discovery of the huge oil deposits in Pennsylvania flooded the world with an inexpensive illuminant. As early as the thirteenth century Marco Polo, the explorer, wrote of a natural petroleum spring at Baku, on the Caspian Sea: "There is a fountain of great abundance, inasmuch as a thousand shiploads might be taken from it at one time. This oil is not good to use with food, but it is _good to burn_; and is also used to anoint camels that have the mange. People come from vast distances to fetch it, for in all other countries there is no oil." His last words have been confuted by the American oil-fields, yielding many thousands of barrels a day--often in such quant.i.ties that the oil runs to waste for lack of a buyer.

The rivals for pre-eminence in lighting to-day are electricity, coal gas, petroleum, and acetylene gas. The two former have the advantage of being easily turned on at will, like water; the third is more generally available.

The invention of the dynamo by Gramme in 1870 marks the beginning of an epoch in the history of illumination. With its aid current of such intensity as to constantly bridge an air-gap between carbon points could be generated for a fraction of the cost entailed by other previous methods. Paul Jablochkoff devised in 1876 his "electric candle"--a couple of parallel carbon rods separated by an insulating medium that wasted away under the influence of heat at the same rate as the rods. The "candles" were used with rapidly-alternating currents, as the positive "pole" wasted twice as quickly as the negative. During the Paris Exhibition of 1878 visitors to Paris were delighted by the new method of illumination installed in some of the princ.i.p.al streets and theatres.

The arc-lamp of to-day, such as we see in our streets, factories, and railway stations, is a modification of M. Jablochkoff's principle.

Carbon rods are used, but they are pointed towards each other, the distance between their extremities being kept constant by ingenious mechanical contrivances. Arc-lamps of all types labour under the disadvantage of being, by necessity, very powerful; and were they only available the employment of electric lighting would be greatly restricted. As it is, we have, thanks to the genius of Mr. Edison, a means of utilising current in but small quant.i.ties to yield a gentler light. The glow-lamp, as it is called, is so familiar to us that we ought to know something of its antecedents.

In the arc-lamp the electric circuit is _broken_ at the point where light is required. In glow or incandescent lamps the current is only _hindered_ by the interposition of a bad conductor of electricity, which must also be incombustible. Just as a current of water flows in less volume as the bore of a pipe is reduced, and requires that greater pressure shall be exerted to force a constant amount through the pipe, so is an electric current _choked_ by its conductor being reduced in size or altered in nature. Edison in 1878 employed as the current-choker a very fine platinum wire, which, having a melting temperature of 3450 degrees Fahrenheit, allowed a very white heat to be generated in it. The wire was enclosed in a gla.s.s bulb almost entirely exhausted of air by a mercury-pump before being sealed. But it was found that even platinum could not always withstand the heating effect of a strong current; and accordingly Edison looked about for some less combustible material. Mr. J. W. Swan of Newcastle-on-Tyne had already experimented with carbon filaments made from cotton threads steeped in sulphuric acid. Edison and Swan joined hands to produce the present well-known lamp, "The Ediswan," the filament of which is a bamboo fibre, carbonised during the exhaustion of air in the bulb to one-millionth of an atmosphere pressure by pa.s.sing the electric current through it. These bamboo filaments are very elastic and capable of standing almost any heat.

Glow-lamps are made in all sizes--from tiny globes small enough to top a tie-pin to powerful lamps of 1000 candle-power. Their independence of atmospheric air renders them most convenient in places where other forms of illumination would be dangerous or impossible; _e.g._ in coal mines, and under water during diving operations. By their aid great improvements have been effected in the lighting of theatres, which require a quick switching on and off of light. They have also been used in connection with minute cameras to explore the recesses of the human body. In libraries they illuminate without injuring the books.

In living rooms they do not foul the air or blacken the ceiling like oil or gas burners. The advantages of the "Edison lamp" are, in short, mult.i.tudinous.

Cheapness of current to work them is, of course, a very important condition of their economy. In some small country villages the cottages are lit by electricity even in England, but these are generally within easy reach of water power. Mountainous districts, such as Norway and Switzerland, with their rushing streams and high water-falls, are peculiarly suited for electric lighting: the cost of which is mainly represented by the expense of the generating apparatus and the motive power.

One of the greatest engineering undertakings in the world is connected with the manufacture of electric current. Niagara, the "Thunder of the Waters" as the Indians called it, has been harnessed to produce electrical energy, convertible at will into motion, heat, or light.

The falls pa.s.s all the water overflowing from nearly 100,000 square miles of lakes, which in turn drain a far larger area of territory.

Upwards of 10,000 cubic yards of water leap over the falls every second, and are hurled downwards for more than 200 feet, with an energy of eight or nine million horse-power! In 1886 a company determined to turn some of this huge force to account. They bought up land on the American bank, and cut a tunnel 6700 yards long, beginning a mile and a half above the falls, and terminating below them. Water drawn from the river thunders into the tunnel through a number of wheel pits, at the bottom of each of which is a water-turbine developing 5000 horse-power. The united force of the turbines is said to approximate 100,000 horse-power; and as if this were but a small thing, the same Company has obtained concessions to erect plant on the Canadian bank to double or treble the total power.

So cheaply is current thus produced that the Company is in a position to supply it at rates which appear small compared with those that prevail in this country. A farthing will there purchase what would here cost from ninepence to a shilling. Under such conditions the electric lamp need fear no compet.i.tor.

But in less favoured districts gas and petroleum are again holding up their heads.

Both coal and oil-gas develop a great amount of heat in proportion to the light they yield. The hydrogen they contain in large quant.i.ties burns, when pure, with an almost invisible flame, but more hotly than any other known gas. The particles of carbon also present in the flame are heated to whiteness by the hydrogen, but they are not sufficient in number to convert more than a fraction of the heat into light.

A German, Auer von Welsbach, conceived the idea of suspending round the flame a circular "mantle" of woven cotton steeped in a solution of certain rare earths (_e.g._ lanthanum, yttrium, zirconium), to arrest the heat and compel it to produce bright incandescence in the arresting substance.

With the same gas consumption a Welsbach burner yields seven or more times the light of an ordinary batswing burner. The light itself is also of a more pleasant description, being well supplied with the blue rays of the spectrum.

The mantle is used with other systems than the ordinary gas-jet.

Recently two methods of illumination have been introduced in which the source of illumination is supplied under pressure.

The high-pressure incandescent gas installations of Mr. William Sugg supply gas to burners at five or six times the ordinary pressure of the mains. The effect is to pulverise the gas as it issues from the nozzle of the burners, and, by rendering it more inflammable, to increase its heating power until the surrounding mantle glows with a very brilliant and white light of great penetration. Gas is forced through the pipes connected with the lamps by hydraulic rams working gas-pumps, which alternately suck in and expel the gas under a pressure of twelve inches (_i.e._ a pressure sufficient to maintain a column of water twelve inches high). The gas under this pressure pa.s.ses into a cylinder of a capacity considerably greater than the capacity of the pumps. This cylinder neutralises the shock of the rams, when the stroke changes from up-to downstroke, and _vice versa_.

On the top of the cylinder is fixed a governor consisting of a strong leathern gas-holder, which has a stroke of about three inches, and actuates a lever which opens and closes the valve through which the supply of water to the rams flows, and reduces the flow of the water when it exceeds ten or twelve inches pressure, according to circ.u.mstances. The gas-holder of the governor is lifted by the pressure of the gas in the cylinder, which pa.s.ses through a small opening from the cylinder to the governor so as not to cause any sudden rise or fall of the gas-holder. By this means a nearly constant pressure is maintained; and from the outlet of the cylinder the gas pa.s.ses to another governor sufficient to supply the number of lights the apparatus is designed for, and to maintain the pressure without variation whether all or a few lamps are in action. For very large installations steam is used.

Each burner develops 300 candle-power. A double-cylinder steam-engine working a double pump supplies 300 of these burners, giving a total lighting-power of 90,000 candles. As compared with the cost of low-pressure incandescent lighting the high-pressure system is very economical, being but half as expensive for the same amount of light.

It is largely used in factories and railway stations. It may be seen on the Tower Bridge, Blackfriars Bridge, Euston Station, and in the terminus of the Great Central Railway, St. John's Wood.

Perhaps the most formidable rival to the electric arc-lamp for the lighting of large s.p.a.ces and buildings is the Kitson Oil Lamp, now so largely used in America and this country.

The lamp is usually placed on the top of an iron post similar to an ordinary gas-light standard. At the bottom of the post is a chamber containing a steel reservoir capable of holding from five to forty gallons of petroleum. Above the oil is an air-s.p.a.ce into which air has been forced at a pressure of fifty lbs. to the square inch, to act as an elastic cushion to press the oil into the burners. The oil pa.s.ses upwards through an extremely fine tube scarcely thicker than electric incandescent wires to a pair of cross tubes above the burners. The top one of these acts as a filter to arrest any foreign matter that finds its way into the oil; the lower one, in diameter about the size of a lead-pencil and eight inches long, is immediately above the mantles, the heat from which vaporises the small quant.i.ty of oil in the tube.

The oil-gas then pa.s.ses through a tiny hole no larger than a needle-point into an open mixing-tube where sufficient air is drawn in for supporting combustion. The mixture then travels down to the mantle, inside which it burns.

An ingenious device has lately been added to the system for facilitating the lighting of the lamp. At the base of the lamp-post a small hermetically-closed can containing petroleum ether is placed, and connected by very fine copper-tubing with a burner under the vaporising tube. When the lamp is to be lit a small rubber bulb is squeezed, forcing a quant.i.ty of the ether vapour into the burner, where it is ignited by a platinum wire rendered incandescent by a current pa.s.sing from a small acc.u.mulator also placed in the lamp-post.

The burner rapidly heats the vaporising tube, and in a few moments oil-gas is pa.s.sing into the mantles, where it is ignited by the burner.

So economical is the system that a light of 1000 candle-power is produced by the combustion of about half-a-pint of petroleum per hour!

Comparisons are proverbially odious, but in many cases very instructive. Professor V. B. Lewes thus tabulates the results of experiments with various illuminants:--

_Cost of 1000 candles per hour._

_s. d._ Electricity Per unit, 3-1/2d.

" Incandescent, 1 2 " Arc, 0 3-3/4 Coal-gas Flat flame, 1 6 " Incandescent, 0 2-1/4 " " high pressure, 0 1-3/4 Oil Lamp (oil at 8d. per gall.), 0 7-1/4 " Incandescent lamp, 0 2-1/4 " Kitson lamp, 0 1

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 the streets 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. _Acetylene_ gas, 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 an _ideal_ illuminant.

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 quant.i.ty of useless light-waves; the oil-lamp that brightens one's rooms gives off a quant.i.ty 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 most perfected 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 ma.s.s of mechanism and consumption of material."[6]

[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 phosph.o.r.escent or "cold" light, illuminating without combustion owing to the absence of all waves but those of the requisite frequency. 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 lit _without_ contact 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 pa.s.sing 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 gla.s.s tubes several feet long, bent into spirals or other convolutions, and filled before sealing with a certain gas. The ends of the gla.s.s tube are coated with metal and provided with hooks to connect the lamp with an electric current. The gas becomes _luminous_ under the influence of current, 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 pa.s.sed 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.