Marvels of Scientific Invention Part 18

Let us first of all examine the principle. Sunlight, by which photographs are usually taken, appears to the eye white and colourless.

It is not really so, however, as can be proved by a.n.a.lysing it with the spectroscope. In this instrument a flat beam of light, having pa.s.sed through a narrow slit, falls upon a prism of gla.s.s, from which it emerges as a broad band, known as the "spectrum." This band can be seen upon a screen, or can be examined through a telescope. So far from being white and colourless, it consists of the most lovely colours. At one end of the spectrum is a beautiful red, which, as the eye travels along, imperceptibly merges into orange, which in turn merges into yellow, after which we find green, blue, indigo and violet, in the order named.

These seven are known as the "primary colours," but it is quite a mistake to suppose that there are seven clearly defined and distinct colours. The colours so change, one into another, that their number is really infinite. The seven names indicate seven points in the spectrum, whereat the colours are sufficiently distinct from others to warrant a separate name being given to them. We call the starting colour red, for example, and as we pa.s.s our eyes along we perceive a constant change, and when that change has become sufficiently p.r.o.nounced to justify our doing so, we call the new colour "orange." Continuing, we find the orange changing into something else, and when it has gone far enough, we bring in a third name, yellow, and so on to the violet. Thus we see the division into seven colours is arbitrary, and only for our own convenience, since the whole number of colours is innumerable.

Pa.s.sing through a prism is not, however, the only means by which white light can be split up. When the sun shines upon a blue flower, for instance, the blue petals perform a partial separation; they reflect the blue part of the sunlight, and absorb all the rest. A red flower likewise reflects the red part of the sunlight and absorbs the rest. It is because things can thus discriminate, reflecting some kinds of light and absorbing the remainder, that we perceive things in different colours.

It follows, therefore, that when we look upon a landscape, or a field of flowers, we receive into our eyes an enormous variety of coloured lights. The white sunlight furnishes each thing we see with a flood of white light, and each thing according to its nature, reflects more or less. A white flower reflects the whole, a pure black object reflects none, but the great majority of things reflect some part or other of that infinite variety of which white light really consists.

So a view at all varied sends to our eyes a variety of colours, almost as manifold as the colours of the spectrum, which, as has been said, are infinite. And the task of reproducing them, or even of producing a similar general effect, upon a piece of paper seems at first sight beyond the bounds of possibility.

But fortunately there is a way by which we can produce, approximately at all events, the intermediate colours by mixtures of the others. The second colour of the spectrum, for example, orange, can be obtained by mixing its neighbours on either hand--namely, red and yellow. We can, indeed, imitate very closely the imperceptible change from red to yellow through orange, by skilful mixture of red and yellow pigments. First there is the pure red, then just a suggestion of yellow is added; more and more yellow brings us to orange; after which by gradually diminishing the amount of red we reach the pure yellow. Next, by introducing blue pigment, we can gradually change the yellow into green, and further manipulation of the same two colours will lead us on to pure blue. Indeed by mixtures of red, yellow and blue we can obtain almost all the perceptible varieties of colour.

And it must be remembered that when, by mixing blue and yellow pigments, we get the effect of green, that is only the result of an optical illusion. The particles of which the yellow pigment is made remain yellow, and the particles of blue remain blue. The one sort reflect yellow light to our eyes, the other sort reflect blue light, and owing to what in one sense may be called a defect in our vision, these two mingling together look as if the whole were green. In the spectrum we see real green light; from green paint made by mixing yellow and blue, we only see an imitation or artificial green. If the particles were large enough, we should see the yellow and the blue ones quite separate, but since they are too small for us to see at all, except in the ma.s.s, our eyes blend the whole together into the intermediate colour.

Thus we see that, although the variety of colours is infinite, we can for practical purposes reproduce as much difference as our eyes can perceive by the judicious blending of three--namely, red, yellow and blue.

And there is a further fortunate fact--we can filter light. The red gla.s.s with which the photographer covers his dark-room lamp looks red, and throws a red light into the room, because it is acting as a filter to the light proceeding from the lamp behind it. The lamp is sending out light of many colours, but the gla.s.s is only transparent to the red. It holds up all the others but lets the red pa.s.s freely. So if we were to take a photograph through a red screen, we should get on the plate only those parts which were more or less red in colour. For example, if we thus photographed a group of three flowers, one red, one orange and one yellow, the red one would come out prominently, the orange one would come out faintly, and the yellow one not at all.

Then suppose we took the same picture again through a yellow screen. In that case the yellow flower would be prominent, the orange would again be faint, but the red would be absent.

Having got, in imagination, two such negatives, let us make two carbon prints, one off each. And let the print off the first negative be red, while that off the second is yellow. Let each be, in fact, of the same colour as the screen through which the picture was taken. Finally, let the two films be placed in contact one upon the other. On holding the two up to the light, what should we see?

We should see a red flower, for there would be a red flower clearly defined upon one film coinciding with a blank transparent s.p.a.ce upon the other film. We should see, too, a yellow flower, for a clearly defined yellow flower on the second film would coincide with a clear s.p.a.ce upon the first. We should see also an orange-coloured flower, for there would be a faint red image of it, and a faint yellow image of it, one on each film, lying one over the other, producing the same effect as a mixture of yellow and red pigments. Thus by taking two negatives through two coloured screens, and then colouring the prints to correspond, we can obtain three colours in the finished picture.

By taking a third negative, through a blue screen, we could add immensely to the range of colours obtainable. Indeed, with three films, red, yellow and blue respectively, made through three screens of the same colour, a variety of colours practically infinite can be obtained.

So the principle is quite simple; the difficulty is in carrying it out.

For the three kinds of light have not the same photographic power, and so to avoid upsetting the "balance" of the colours different exposures would be required for each. Then there is the difficulty of so manipulating the films as to get them one over another exactly. Anyone who has tried the handling of carbon prints will readily realise how difficult this would be. It is possible and has been done, but the process is too uncertain and too laborious to be of general use.

But the same result can be attained more or less automatically, as the following descriptions will show.

Let us turn to the Lumiere autochrome process, by which the results desired can be in a large measure attained by methods of manipulation comparatively simple.

[Ill.u.s.tration: _By permission of The Mining Engineering Co., Ltd., Sheffield_

PNEUMATIC HAMMER DRILL

This tool is used by miners for making holes in hard rock, preliminary to blasting. Note the spray of water, which prevents the stone dust rising and getting into the miner's lungs.--_See_ p. 220]

The plates used for this are of a very special nature. In the first place, there is the basis of gla.s.s, but upon that there is laid what we might term the selective screen. This is a layer of starch grains, of exceeding smallness. The size of them is as little as a half a thousandth of an inch and there are about four millions of them on every square inch of plate. Next, upon the screen of starch grains is a layer of waterproof varnish, while over that is the ordinary sensitive emulsion such as forms the essential part of the usual non-colour plate.

Now the starch grains which form the screen are, before they are laid on, stained in three colours. Some are blue, some red, and some a yellowish-green, which experience shows is preferable to pure yellow.

The differently coloured grains are well mixed, and when the screen is held to the light and looked through the effect is almost that of clear gla.s.s. That is because red rays from the red grains, and green and blue rays from the grains of those colours, all proceed to the eye mingled together.

This plate is placed in the camera differently from the usual way, since the gla.s.s side is turned towards the lens. The light, therefore, after entering the camera, pa.s.ses through the gla.s.s, then through the screen, and finally falls upon the sensitive film.

Suppose, then, that the camera were pointed to a red wall; red light would fall upon the plate and, pa.s.sing through the red grains, would act upon the sensitive film behind them. The blue and green grains, on the other hand, would stop those rays which fell upon them, and so those parts of the sensitive film which they cover would remain unaffected by light. Then, if that plate were to be developed, a dark, opaque spot would be produced upon the film under each red grain, the film under the other grains remaining transparent. Hence, when held up to the light and looked through, the plate would appear a greenish-blue, for all the red grains would be covered up.

In like manner, if the wall were blue instead of red, a greenish-red plate would result, while if it were green, the plate would be a purple, the result of the combination of red and blue.

But this, it will be seen, is a topsy-turvy effect, the exact opposite of what we want, so that it is fortunate that by a simple chemical method we can set it right. After a first development in the ordinary way the plate is placed in another bath and exposed to strong daylight, with the result that those parts which were darkened by the first development become clear and the parts which were clear become opaque.

Thus, after this twofold development of the photograph of the red wall, we find ourselves in possession of a red plate, in which only the red grains are visible, since all the others are covered up by opaque parts of the sensitive film. The photograph of the blue wall will also, after it has been subjected to the double development, show blue only, and the same with the green.

But suppose that instead of a red wall or a blue wall we focus our camera upon one which is half red and half blue. Then it is easy to perceive that we shall get a plate which is half one colour and half the other. Moreover, it follows that a wall covered with a mosaic of red, blue and green would give us a plate duly coloured in the same way.

But when we go a step further and photograph, say, a landscape, which may contain a vast range of colours, we find a difficulty in believing that they can all be rendered by the simple process of covering or leaving uncovered grains either blue, red or green. It can be done, however, since the other colours may be made up of two or more of these three in varying proportions. For example, should there be something in the landscape of a darker, more blue, shade of green than the green grains, then the light proceeding from that object, while pa.s.sing freely through the green grains upon which it falls, will slightly penetrate the neighbouring blue ones as well, and so at that point on the plate there will be not only green grains visible, but some of the blue grains partly visible also. The light from the blue grains will enter the eye along with that from the green grains, and by so doing will add just that amount of blue to the green as to give it the right shade.

After this manner is the whole picture built up. It is, of course, really a mosaic, consisting entirely of little coloured patches, but since they are so small none can be seen individually, all merging together in the eye so as to form a picture in which colours change imperceptibly from one into another.

To sum up, then, what happens is this. We start with a layer of coloured grains; the action of taking and developing the photograph covers up some of these grains and leaves others exposed, and the action of the light is such that those which are left visible produce a picture closely resembling the original, not only in form but in colour.

But there is one other interesting point about this process which deserves mention. The differently coloured lights are not of the same power photographically. Red light, as we know well, is very weak in this respect, wherefore, we use it in the dark-room. A faint red light will have no perceptible effect upon a plate unless it be exposed to it for some time. Blue light, on the other hand, is very active, and were the blue and red lights to be allowed to act equally on the autochrome plate, the result would be much too blue. It is therefore necessary to handicap the blue light, as it were, by placing a "reddish-yellowish"

screen either just in front of, or just behind, the lens to cut off a proportion of the blue rays.

The other very successful process is known as the Dufay dioptichrome process. It differs very little from the Lumiere except in detail, the selective screen being formed of small coloured squares instead of by a ma.s.s of little grains.

In both, it will be noticed, the result is a single positive. It is not, as in ordinary photography, a negative off which any desired number of positive prints can be made. And, moreover, it is a transparency: it cannot be viewed except by light shining through it. The results are, however, extremely beautiful, when well done, and anyone who cares to try either of these methods of working will be well repaid for the trouble involved.

CHAPTER XVII

HOW SCIENCE AIDS THE STRICKEN COLLIER

Nothing is more characteristic of the present age than the care which is, quite rightly, expended upon the comfort and safety of those who do the manual labour of the community. The stores of scientific knowledge and skill are drawn upon freely for this end, and some very interesting examples can be given of the truly scientific methods which have been evolved, not only for preventing injuries of any kind, but for succouring those who may, despite those precautions, fall victims to disease or accident.

An example has already been given of the scientific investigation into the nature of colliery explosions and the best means of preventing them.

We have seen there how expense has been poured out lavishly in fitting up the experimental gallery or artificial pit, and how the most cunning mechanical and electrical devices have been pressed into the service in order to find out just what happens when an explosion occurs. It has been related how these investigations have revealed with certainty the true cause of the explosions and thereby led the way to their prevention.

But with it all there is still an occasional disaster, occurring, sometimes, at the best and most carefully managed collieries. And therefore it is still necessary to provide for rescuing the unfortunate men who are affected.

It is worth remark, here, that colliery explosions are, all things considered, a very rare occurrence. Because of their dramatic suddenness, and the number of lives which are commonly lost in a single disaster, we are apt to magnify their severity in our minds and to picture the life of the miner as a very hazardous one. In point of fact, the expectation of life, as the insurance people call it, is quite as great among the coal-miners as among any cla.s.s of manual labour. And of those who do meet an untimely end there are more lost through isolated accidents, involving one or two men, than in the great disasters.

To meet these isolated cases science is almost powerless. For the most part, they are due to falls of material from the roof of the mine, or some simple accident of that kind, caused by an error of judgment or lack of care on the part of fellow-workmen, and the only safeguard against such is the most careful and systematic supervision, which, in Great Britain at all events, is rigidly applied. The underground staff are very carefully organised with this end in view, and the whole is supervised by Government inspectors. No amount of scientific investigation or invention will help much in these matters.

With the explosion or fire, however, it is different, for there subtle forces and strange chemical influences come into play with which science is specially well fitted to deal.

To a great many people the first news of organised, trained and scientifically equipped rescue parties came at the time of the terrible Courrieres disaster in France, when over 1000 men lost their lives. For then a party with apparatus hurried from Germany and played a prominent part in the rescue operations. But unfortunately the glamour of their performance was somewhat dimmed by the fact that after they had done all they could, and had gone home again, more men were rescued. Many, reading of that fact, were inclined to scoff at the "new-fangled" ideas, thinking that after all the old way of working with a party of brave but untrained and often ignorant volunteers was better than the new way of working with equipped and trained men. It certainly did seem as if the former had succeeded where the latter had failed. But that was quite a mistake, as subsequent events have shown, and in all probability it was due to the fact that the uninstructed party were local men, thoroughly familiar with the mine in which they were working, its geography and its special local conditions, whereas the trained men came from far away.

At all events the pioneer work of the Germans in the matter of rescue teams has been amply justified by the fact that other people have copied them, and none more thoroughly than the mining authorities of Great Britain. Indeed we see here another instance of the remarkable way in which the British people, though a little slow to take up a new idea, do take it up when it has once been established, and in such a way that they are soon among the foremost in its use. The Germans, all honour to them, started the rescue teams, but at this moment there are rescue teams and stations for their training in Britain second to none in the world. Of these there is a splendid example in the Rhondda Valley, in South Wales, supported and worked by the owners of the pits in that district, besides others at Aberdare, in the same neighbourhood, at Mansfield, to serve the collieries in Derbyshire and Nottinghamshire; indeed rescue stations are now dotted throughout the mining districts.

The general idea of these stations is as follows. The building is centrally situated in the district which it is intended to serve, and in it are kept an ample supply of the necessary appliances, in the shape of breathing apparatus, which enables men to walk unhurt through poisonous gas, reviving apparatus, by which partially suffocated men can be brought round again by the administration of oxygen, together with quant.i.ties of that valuable gas in suitable portable cylinders.

Everything which forethought can suggest as even possibly useful in an emergency is kept in a constant state of readiness. And all the while a swift motor car stands ready to carry them to the scene of operations.

But the appliances are of little use without men to work them, who know them and can trust them. The case of David, who felt able to do better work with his sling and stone than in all the panoply of Saul's armour, because he "had not proved it," is typical of a universal human instinct. A man feels safer unarmed, or simply armed, than he does with the most elaborate weapons in which he has not learned to have confidence. And therefore the men who may be called upon to work this apparatus are first taught to have confidence in it. Each station has its instructor, who is usually also the general superintendent of the station, and "galleries" in which the instruction can be carried out.

Volunteers are called for in each colliery and a number of the most suitable men are chosen to undergo training, preference being given, very naturally, to those who are already trained, as fortunately so many workmen are nowadays, in ambulance work.