Read no history: nothing but biography, for that is life without theory. — Disraeli

Twentieth Century Inventions - Charles Gibson

Miscellaneous Inventions


Colour Photography

The practical methods of producing coloured photographs in the nineteenth century required the taking of three separate negatives, through red, green, and violet screens, from which three transparent positives were obtained. In order to view the photographs it was necessary either to shine three lights of the primary colours through the three transparencies (Ives process), or dye the transparencies the three complementary colours and superimpose them (Sanger-Shepherd process). There were exceptions, such as Lippmann's interference films and Wood's diffraction grating process, but these were entirely of scientific interest. Then came the Joly process, in which an attempt was made to put the three colour screens upon one glass plate, by ruling very fine parallel lines (red, green, and violet) all over the plate. The result is a finely-lined negative, from which a positive may be made and viewed through the colour-lined screen.

In the twentieth century a considerable advance has been made. In 1907, Auguste and Louis Lumiere, of Paris, invented a practical method of securing the three-colour impressions on one plate. They took potato starch, and converted it into round particles which are microscopic, measuring only about

nth part of an inch. These fine starch-grains were then divided into three portions and dyed, one portion orange-red, another green, and the third violet. They are then mixed together by a special machine, and the resulting powder is of a grayish colour. This powder is spread over a glass plate which has been covered with a film of gelatin. Some pressure is then applied so that the edges of the spherical grains touch as far as that is possible. The small interstices remaining are filled with very finely-divided carbon to prevent any white light getting through. This fine grain structure is then protected by a film of varnish, and on the top of this is applied the photographic emulsion, which, of course, must be panchromatic (sensitive to all coloured lights). All such emulsions are more sensitive to violet rays, and for this reason, in exposing the plate in the camera, the light is filtered through a yellow screen to subdue the violet rays.

The plate is exposed in the camera with the glass side towards the lens, and so the light passes through the coloured starch grain before it reaches the sensitized film. Red light can penetrate only the red starch grain, so that all the red rays will record their impression beneath red granules, green beneath green, and violet beneath violet granules. The light from a yellow object will register beneath the red and the green granules, as a yellow object reflects both red and green rays, and so on.

In developing the negative, the silver salt which has been exposed to light is reduced and obscures these granules which have transmitted light, and exposes those which have not permitted light to pass. If the negative be examined it will be found that what has been obtained is just the reverse of what is wanted. Where red light fell upon the plate, the red granules being obscured, the light will pass through the green and violet granules, producing a greenish-blue colour in place of red. Before fixing the chemicals on the photographic emulsion, however, the plate is immersed in a solution of potassium permanganate and sulphuric acid, which dissolves the reduced silver, but does not affect the silver salts which were protected by the coloured granules. The parts of the sensitized film upon which red light fell have the silver reduced by the action of the light; now that is dissolved, leaving the red granules transparent instead of obscure as at first, and so on with the green and the violet.

The next step is to take the plate, the chemicals being yet in an unfixed condition, and expose it to light for a short time, and then develop it for the second time. This will reduce the silver which had been protected formerly, so that in a part of the film which had been exposed to red light, the silver salts behind the green and violet will be covered by an opaque layer of reduced silver. Thus we get the true colours of the objects from the unobscure granules, and the reproduction of colours is wonderfully correct.

More recently the Paget process has been invented, but this is an adaptation of the Joly process, putting the colours on a screen in the form of tiny squares instead of in parallel lines. This process requires the registration of a colour screen in reproducing, as in the nineteenth century processes.


A few years ago two inventors (Urban and Smith) took out a patent for applying colour photography to kinematography. This was no easy matter. Already the moving pictures had to pass the lens at the rate of about one thousand per minute (sixteen per second). To throw red, green, and violet pictures in quick succession would mean an exposure of nearly 3000 pictures per minute, both in the taking and in the reproduction.

The inventors made a compromise; they were satisfied to use two components, red and green only. The long film in the kinemacolor contains alternate pictures taken through a red and a green screen, and these have to be reproduced time about through these two coloured screens. The kinematograph is driven twice as fast as usual, making about thirty-two exposures per second, and a revolving disc, containing a segment of red screen and a segment of green, revolves in front of the lens, in perfect step with the moving pictures. Of course, those colour combinations in which violet plays a prominent part must appear of a nondescript colour. The red, orange, yellow, and green can be fully represented, and the general colour effect is very good.

Thermit Welding

This invention, made by Dr Hans Goldschmidt, depends upon a very vigorous reaction between certain compounds. The object is to give a convenient method of welding without any heavy furnace or other apparatus. For instance, to weld a tramway rail by this process, while in position in the track, it is only necessary to place a simple mould around the joint and clamp a crucible on the mould. The crucible is filled with 'thermit,' and the reaction is started by a flame or by a red-hot iron bar.

Thermity is a mixture of a metallic oxide (usually iron) and pulverized aluminum, and when the reaction is once started between these two compounds the temperature quickly rises to about 3000 degrees. At this temperature the metal (say iron) of the oxide is given off in a pure state, free of carbon, and the pulverized aluminum unites with the oxygen of the oxide, and forms oxide of aluminum. The molten iron falls to the bottom of the crucible, and the light aluminum slag floats on the surface. A tap-hole is formed in a magnesia brick at the bottom of the crucible, and the hole is covered by a metal disc protected by two discs of asbestos. This plug or cover may be pushed in by means of a pin and lever, whereupon the mass of molten metal will flow from the crucible into the mould formed around the rail. The welded portion is found to be stronger than the rail itself, and under hydraulic pressure the break occurs outside the welded zone, the shoe of iron welded around the foot and web of the rail giving that part the additional strength. The process is of wide application, not being in any way confined to the welding of rails.

Cutting Metals By A Flame

A well-known laboratory experiment is to burn iron nails or a steel watch-spring in an atmosphere of oxygen. The knowledge of this grabbing power of iron for oxygen is very old, but not till 1901 was it put to any practical use. The first application was to use an oxyhydrogen flame to remove solidified iron from the blow-holes of blast furnaces, but a few years later (1904) a new application was made, the cutting of heavy sheets of metal.

In 1909 it was found possible to cut through a 9-inch armour-plate of chrome steel, by means of an oxyhydric flame. The invention does not consist in merely blowing an oxyhydrogen flame upon the metal, but in blowing a high-pressure oxygen jet from a second nozzle, deflected so that the jet strikes the metal pre-heated by the oxyhydric flame. As this tool is moved along, the heating flame keeps bringing fresh metal to the combustion point, and the molten oxide which is formed on the surface is easily blown away by the high-pressure oxygen jet. The temperature is only about 1500 F., at which heat the iron has a great affinity for oxygen. The heat is confined to a narrow line, the properties of the materials cut not being affected beyond a1th of an inch of the cut surface. The result is a clean and narrow cut, just as though it had been made by some great knife.

When cutting very thick plates, a second heating nozzle may be added, but the principle is the same throughout, and even armour-plate of two feet in thickness may be cut through by the oxyhydric process. The cut need not be a straight line, but can be in a curve or any desired shape. The same principle may be applied to the cutting of apertures in plates or tubes, bolt holes in fish-plates, and such like.

The oxygen and hydrogen are stored in cylinders under a pressure of about 2000 pounds per square inch. Each cylinder has a needle-valve controlled by a pressure-regulator. The gases pass through heavily-armored tubes to the mixing chamber, which is surrounded by cold water to prevent any risk of explosion of the mixed gases. From the mixer the gases pass to the cutting tool.

Blasting With Liquid Air

We have become quite familiar with the idea of ordinary air in a liquid condition, and many experiments with it are well known. Model locomotives and even full-sized motor-cars have been driven by its expansive force.

We know that the boiling point of liquid air is 190 degrees below the zero of the Centigrade scale (—300 F.). We require no very lively imagination to picture the result of liquid of that temperature coming in contact with masses of rock, the normal temperature of which is about 350 F. higher. There will be a very energetic exchange of temperature by heat conduction from the rock to the liquid, which will cause the liquid air to vaporize at an enormous rate. Indeed the difficulty in using liquid air in explosive cartridges was to prevent the air vaporizing before it was possible to fire the explosive. But during the early part of 1913 there was invented a reliable means of blasting with liquid air.

The invention is based upon a discovery which was made soon after the successful preparation of liquid air in quantities. It was found that charcoal at a low temperature was a great absorber of gases, and that a mixture of liquid air and charcoal may be highly explosive, when ignited by means of cartridges and fuses. The first attempts to put this discovery to practical use in mines was not encouraging, but two German engineers have now overcome the obstacle. Working in the Royal Quarries of Rudensdorf (near Berlin), the inventors conceived the idea of keeping the dry carbon and the liquid air separate until the explosive mixture was to be used. They introduced the cartridges with dry carbon into the blast-holes, and only added the liquid air when they were about to cause the explosion.

No dynamite or other explosive is used. A substantial pasteboard cylinder filled with an absolutely inert mixture of Kieselguhr and oil, asphalt, soot, or paraffin, is introduced into the blast-hole. This paper cylinder has a central tube which is perforated, and into which there is led a small supply tube, also made of paper. This small tube is to convey the liquid air to the cartridge when desired, and in order to discharge any products of vaporization of the liquid air, this tube has an outer jacket through which these products may escape. Several blast-holes may be fired simultaneously, all being connected by conductors to the igniting battery.

The liquid air is kept ready for each blast-hole in a special flask containing the required amount. These flasks carry at their opening a flexible metal tube, into which the central supply paper-tube is fitted. When the back end of the flask is lifted, the liquid air, under the pressure of its own products of vaporization, rises through the metal tube and through the paper tube into the cartridge. When the electric ignition takes place, the chemical combinations are so violent that a terrific explosion occurs.

This invention does away with the transport and storage of dangerous explosives, the liquid air plant being situated at the mine.

Nitric Acid From The Atmosphere

For a century and a half we have known that an enormous store of nitrogen was all around us in the atmosphere, of which that element composes no less a proportion than four-fifths, but we had no means of obtaining this nitrogen in the form of nitrates, which are of great value as manures.

It is true that Cavendish showed how the nitrogen and oxygen of the air could be combined to form nitrous oxide by means of electric sparks, but it took Cavendish and his assistant a fortnight's continuous work day and night to produce an appreciable quantity of nitrous oxide. This compound is formed by combining equal quantities of nitrogen and oxygen. The compound nitrous oxide (NO) will combine with oxygen to form nitrogen peroxide (NO2), and this gas is soluble in water (H20), with which it combines to form nitric acid( HNO3)

The twentieth century invention, by which nitric acid is obtained from the atmosphere, is practically Cavendish's old experiment on a very much larger scale. Several powerful electric arcs, with a potential of 33,000 volts, are produced in a dome-shaped combustion chamber. The air is admitted by means of a valve into the combustion chamber, where it is exposed to the intense flame of our arcs. The gases which leave the combustion chamber are nitric oxide, free nitrogen, and free oxygen. These gases are conducted to the combining vessels, in which the nitric oxide and the oxygen combine to form nitrogen peroxide. The gases then pass to the dissolving towers, where the nitrogen peroxide is dissolved in water to form nitric acid, and the free nitrogen escapes to the air.

The different processes, invented for the fixation of atmospheric oxygen, are all based upon the same general principle. The electrodes may be made of iron, and kept cool by water-circulation; they are able to withstand 200 working hours. Factories of 10,000 and 15,000 horse-power are at work.

Thunder-Storm Detector

Professor Turpain, of the Universite de Poitiers (France), has invented several instruments for recording and detecting approaching thunder-storms. As these instruments are to record electric impulses travelling through the tether of space, they are provided with aerials, and are in principle wireless receivers.

One of the most interesting forms of detector used by Professor Turpain is a coherer composed of a number of sewing needles placed crosswise, providing the orthodox loose contacts required in all coherers. The resistance in these loose contacts is sufficient to bar the way of a local battery current, but as soon as the incoming electric impulses from the tether are conducted by the aerial to the needles, they 'cohere' and allow the battery current to reach and operate the recording instrument. As soon as the local battery current rises to a certain point it causes an electro-magnet to operate a hammer and tap the board upon which the needles are held, and in this way they are decohered, and thus cut off the local battery, until a fresh charge is received from the aerial.

The recorder does not merely register the make and break of a sudden charge and discharge, but a sensitive galvanometer records the weak current passing through the needle contacts before their resistance is reduce I sufficiently to pass a current capable of operating the tapper. The galvanometer makes its record by means of a light pen upon a clockwork cylinder, similar to that of an ordinary barograph. Indeed the thunder-storm recorder is arranged sometimes to make its record alongside of a barograph on the same cylinder. The recording pen will be moved up and down leaving a tracing on the moving paper, then when the current rises high enough to operate the tapper, the pen will fall down to zero, and commence a fresh rise and fall, and so on. Of course, if the thunder-storm happened to be very distant, the varying record might be continuous for a long time, without the current ever rising high enough to operate the tapper and bring about a decoherence. By means of such instruments an approaching thunder-storm may be detected several hours before it arrives. Professor Turpain has devised a more sensitive form of recorder, in which a mirror galvanometer throws a beam of light upon a moving band of photographic paper. The mirror galvanometer is connected across a Wheatstone bridge, in which two very fine platinum wires are balanced against German-silver resistances. The fine platinum wires are protected from any local changes of temperature by being placed in double-walled silvered-glass vessels, made on the principle of the Dewar flask for holding liquid air (a vacuum space between the double walls). These platinum wires are connected to the aerial, and the electrical charge will heat the wires sufficiently to alter their electrical resistance, upsetting the electrical balance of the Wheatstone bridge, and causing the local battery current to flow through the mirror galvanometer. A more accurate reading of the thunder-storm may be obtained in this way, but the Wheatstone bridge apparatus requires careful adjustment and more attention than is demanded by the simple coherer apparatus.

Mercury Telescope

In 1908 Professor R. W. Wood (U.S.A.) invented a reflecting telescope, in which the magnification was obtained by a concave reflector of liquid mercury. The problem was how to rotate a basin of mercury without producing ripples on the surface of the mercury.

He tried many methods of transmitting the driving power to the basin. In one of these plans he had a rotating ring or collar surrounding the basin, but not touching it. On this ring he fixed a number of horse-shoe magnets, and on the basin he fixed a similar number of magnets. The opposing poles of the magnets faced one another in close proximity, but did not touch. When the outer ring was rotated, its magnets pulled the basin round also. However, it was found that the steady rotation of the mercury was quite as satisfactory when the power was conveyed directly to the basin by means of fine threads of India-rubber attaching the basin to the rotating ring.

The circular flat-bottomed basin is filled to a depth of half an inch with mercury, and when this is rotated with a uniform velocity the surface of the mercury assumes the form of a perfect concave paraboloid under the action of centrifugal force. With the low velocity of twelve revolutions per minute, the surface gives a focus of fifteen feet, while at a speed of twenty revolutions per minute the focal length is about three feet. It requires fully two minutes, after being set in motion, for the mercury to attain the same velocity as the basin. The mercury begins to spin first along the rim of the basin, the motion being gradually transmitted toward the centre.

The inventor describes his apparatus in the Astrophysical Journal and in the Scientific American, and he says: "As we stand beside the dish and watch the reflection of the room in the surface of the liquid, the effect is quite startling. The room appears to expand in a most remarkable manner, the ceiling retreating to a great height, and the walls moving outward."

The tube of the telescope consists of a cement pit fifteen feet deep and thirty inches in diameter. A chamber at the bottom of the pit contains the mirror and the electromotor, and access is obtained to this chamber by means of a separate shaft placed six feet from the telescope shaft. The actual observing, however, is done at the mouth of the pit. The star images are formed a little above the mouth of the pit, where they can be examined with an eye-piece.

Professor Wood tells of an amusing experience with an old inhabitant of the district in America in which his mercury telescope was erected, and the old man's philosophy will make a fitting sentence with which to close this little volume dealing with some of the twentieth century inventions.

The old man happened to come along as the inventor was examining the Milky Way, and the mouth of the telescope pit, which was formerly an old well in a shed adjoining a barn, was filled with hundreds of star images.

"What are they anyway?" asked the old man.

"Suns like ours, only bigger," replied the scientist, whereupon the old man queried,—"You don't say so; and have they earths and things going round 'em, and are they all inhabited?"

"Very likely," said the scientist; "Some people think so."

The old man scratched his head and turning to the scientist, he said,

"Well, do you know, I dunno as it makes so much difference after all whether Taft or Bryan is elected."