By permission of The Mining Engineering Co., Sheffield A Miners' Rescue Team These men are equipped with breathing apparatus which enables them to pass safely through the deadly fumes after an explosion, to rescue their unfortunate comradesBy permission of The Mining Engineering Co., SheffieldA Miners' Rescue TeamThese men are equipped with breathing apparatus which enables them to pass safely through the deadly fumes after an explosion, to rescue their unfortunate comrades
In the instances mentioned, a thousandth of an inch either way has been mentioned as the limit of inaccuracy, or the "tolerance," as it is sometimes termed, but often the limits are much narrower than that. The gauges themselves are a case in point, for they must be true within, say, a ten-thousandth, or even less. And they too are checked by master gauges of a finer degree of accuracy still, being made by the most laborious methods, and checked over and over again, so as to reach the utmost limits in the way of correctness.
So this methodical "scientific" system of "limit gauges" is based upon the principle of having one gauge limiting the error one way and another defining it in the other. Anything simpler or more effective it would be impossible to conceive. It is due very largely to this system that many manufactured articles are now so much cheaper than they used to be. For it enables each individual part to be made wholesale on a large scale, by machines specially adapted to the work, operated by men specially trained to work them, with the practical certainty that these parts when assembled together will fit each other.
In conclusion, there is another very interesting instrument which was first made for a purely utilitarian use—namely, the investigation of the methods of making coloured glass—but which has since been applied to some interesting problems in pure science. It is called the "ultra-microscope."
It must first be pointed out that there is a limit to the power of the ordinary microscope, beyond which the skill of the optician cannot go. He is baffled at that point not because of any lack of ability on his own part, but because of the nature of light itself. An opaque object, unless it be self-luminous, which few things are, can only be seen by reflected light. Generally speaking, we see things because they reflect in some degree the light which falls upon them. But light consists of waves, and when we reach an object so minute that its diameter is about half the wave-length of light, then we cannot see it because it is unable to reflectthe light on account of its smallness. We can see this any day by the seaside, or by a river or large pond. There it is evident that the waves and ripples are reflected by such things as large stones, wood posts or anything of any size which come in their way; but when a wave encounters an object much smaller than itself it simply swallows it up, as it were, flows all over it or around it, without being in any way reflected by it. And it is just the same with the waves of light; they are unaffected by obstacles below a certain size, and so are not reflected by them. For this reason things smaller than about a seven-thousandth of a millimetre cannot possibly be seen by a microscope in the ordinary way.
But if an object can be made self-luminous, then it can be seen, whatever its size, if the magnifying power of the microscope be great enough. So this ultra-microscope, as it is called, is really an ordinary microscope of the highest power possible, with an added apparatus for making the tiny particles which are being sought for self-luminous. This is done by directing upon them a pencil of light of exceeding intensity. Generated by powerful arc lamps, the light is concentrated by a system of lenses until it is of an almost incredible brightness, after which it falls upon the object.
Now at first sight this seems to be no different from the usual procedure with a microscope, and there appears to be no reason why it should be more successful, but the explanation is this: light is a form of energy, and the waves of this very intense beam, falling upon the object, throw it into a state of violent agitation, by virtue of which it shines, not with reflected light, but with light of its own. It is not that the waves are reflected, but that they so shake up the particle that it gives off light waves itself. And thus it comes within the range of human vision.
In this way, not only have the very small particles of colouring matter in glass been seen individually, but it is thought that the actual molecules of matter have been seen,or if not the molecules individually, little groups of molecules, dancing and capering about, just as scientific people for years have believed them to be doing, although they could not see them. So here we have an instance in which manufacture has aided science—an inversion of the usual order of things.
Photography has introduced many of the general public to a branch of practical science which otherwise they would never have cared much about. The action of light upon certain chemicals, the subsequent action upon the same of other chemicals, such as developers, toning solutions and so on, form a very well-known region of the domain of science. And this is, too, a branch of chemistry in which the practical inventor has been very busy. The efforts, therefore, which have been made to invent ways of producing photographic pictures which shall give to the objects their natural colours, will probably be of special interest in a book like this.
Of these there are two very well-known systems, and to them we will mainly confine our attention.
It should first be pointed out, however, that what we are discussing is quite different from the simple "orthochromatic" plates which are used by many photographers. These latter are coated somewhat differently from other plates, with a view to their giving a more realistic picture, but the result is still in one colour. They are, in fact, a little more sensitive to differences in colour than ordinary plates, so that colours which appear, when the latter are used, very much the same, appear, when orthochromatic plates are employed, a little different. But the difference in colour in the object photographed is only, even then, represented by a difference in shade in the picture. The object is, it may be, in many colours, in all the colours, very likely, but the picture is only in one.
And the step from that to a coloured picture is a very longone. True, the solution of the problem is very simple in principle, yet the practical difficulties are so great that even now they have not been entirely overcome.
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 analysing it with the spectroscope. In this instrument a flat beam of light, having passed through a narrow slit, falls upon a prism of glass, 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 pass our eyes along we perceive a constant change, and when that change has become sufficiently pronounced 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.
Passing 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 likewisereflects 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 whichthe 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 mass, 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 glass 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 glass is only transparent to the red. It holds up all the others but lets the red pass 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, letthe 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 space 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 space 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 Lumière autochrome process, by which the results desired can be in a large measure attained by methods of manipulation comparatively simple.
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. 220By permission of The Mining Engineering Co., Ltd., SheffieldPneumatic Hammer DrillThis 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.—Seep. 220
The plates used for this are of a very special nature. In the first place, there is the basis of glass, but upon that there is laid what we might term the selective screen. Thisis 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 glass. 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 glass side is turned towards the lens. The light, therefore, after entering the camera, passes through the glass, 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, passing 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 passing 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 Lumière except in detail, the selective screen being formed of small coloured squares instead of by a mass 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.
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 expectationof life, as the insurance people call it, is quite as great among the coal-miners as among any class 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 Courrières 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 wereworking, 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 quantities 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.
These chosen men then repair at intervals to the station to undergo a proper course of instruction. The instructor, often an ex-non-commissioned officer in the Royal Engineers, accustomed, therefore, to engineering matters, and also to systematic discipline, there puts them through a course of drill the object of which is to teach them to work together as a squad under the orders of a properly constituted chief. Thus when called upon in some emergency there will be no confusion, but each man will know what to do, and a few short words of command from the chief will serve better than the long explanations which would be necessary with an undisciplined body. It welds the individual men, as it were, into a smoothly working machine, thereby increasing the efficiency of the whole. And arrangements are made whereby, should the leader fail, another man steps into his place of authority at once and without question.
Then, having thus brought them under a suitable discipline, the instructor takes his men into the experimental gallery. This may be described as a long, low, narrow shed, in which are timber props and beams, rails on the floor, heaps of coal, all things, in fact, which may tend to make it closely resemble the actual workings of a coal-mine after they have been shaken and shattered by the force of an explosion.
The great difficulty, in a real disaster, arises from what are known as "falls." The roof of the mine is normallysupported by timbers, and these the explosion moves, so that in places many tons of the earth of which the roof of the mine consists will fall and block completely the "roads" or tunnels which communicate from the shaft to the places where the men are at work. These, of course, have to be removed or burrowed through before the men imprisoned in the distant workings can be reached. The rescue party do not, of course, wait to clear away the whole of this debris, only just enough to enable them to crawl through or over it, but even then it often represents the waste of precious hours, and the expenditure of great exertions, to get past a "fall." So at intervals "falls" are made in the gallery, in order that men may be practised in dealing with them.
By permission of W. E. Garforth, Esq., Pontefract An Artificial Coal Mine These two photographs show the clouds of flame and smoke issuing from the mouth of the "Artificial Coal Mine" during the experiments described in the textBy permission of W. E. Garforth, Esq., PontefractAn Artificial Coal MineThese two photographs show the clouds of flame and smoke issuing from the mouth of the "Artificial Coal Mine" during the experiments described in the text
It may be interesting to give a brief statement of the training undergone by the men at the Mansfield Rescue Station. In that case, it should be stated, the gallery is made double, so that men can go one way and return the other back to their starting-point. Having donned their breathing apparatus, they enter the gallery, which, by the way, is filled with smoke and foul gas. Passing along it, they encounter two falls, which they must get over or through; then they have to set twelve timber props as might be necessary to maintain the safety of a damaged road in the mine; all that they do three times over. Then they are required to bring up and lay 250 bricks, a thing which might also be necessary in an actual emergency, after which they have to fix up "brattice cloth" in a part of the gallery. One of the first duties, of course, for a rescue party is to restore the circulation of air in the mine, and brattice cloth is a rough kind of cloth which is put to guide the air currents. That done, they have to take a dummy representing a man of 14 stone, put it on a stretcher, and carry it round the gallery and over the falls. Finally, they restore the timber, bricks and cloth, and their turn of work is done. The total time required for this is two hours, and during the whole of that period they are, of course, breathing not the natural air, but the artificialatmosphere provided for them by the apparatus with which each man is provided. The chief point of this part of the training, as has been remarked already, is to accustom the men to the wearing of the apparatus and to doing work in it. By this means they gain confidence in it, and get to know that it will not fail them in the time of trial.
The course of instruction consists of ten drills such as has been described, after which the men are called up twice a year, just to refresh their memories.
One side of the gallery is glazed, so that the instructor can watch his men at work without of necessity being inside himself, and there are emergency doors as well, which can be opened to let a man out should the ordeal be too much for him. The necessary "fumes" are generated in a stove and driven into the gallery by a fan. The stations are beautifully fitted up, with baths for the men to wash after their somewhat dirty experience in the gallery, and everything is done for their convenience and welfare.
The advantage of this systematic training of a great number of men is that there are men at each colliery who can be called upon when needed. The team of strangers, as has been remarked, partially failed at Courrières, largely because they were strangers, but when every colliery has a team ready, composed of its own men, then clearly there is the greatest chance of success. The central station of the district is the training-ground where the men go from all the collieries to get the experience and instruction, and where a reserve store of appliances is kept. In many cases, of course, the collieries have their own appliances, so that work can be begun at once, without having to wait for that from the rescue station, but the latter forms a reserve in case of need, and, being kept under the care of an expert, it is naturally always in the best possible working order.
To give an idea of the cost of these stations, it may be stated that the one at Porth, in the Rhondda Valley, cost, including equipment, £7000, while the one at Mansfield cost £3000. This first cost and the expense of maintenance isborne by the collieries of the district in proportion to the quantity of coal which they raise.
And now we can turn to the apparatus itself, without which the organisation already described would be of little value.
There are several makes of these, but a description of the particular apparatus used at the two stations mentioned will serve as an illustration. The purpose, of course, is to give the wearer an atmosphere of his own, which he can carry about with him, and which will render him quite independent of the ordinary atmosphere and quite indifferent to the poisonous nature of the gases around him. To this end his mouth and nostrils must be cut off from the outer world altogether. There are two ways of doing this. In the one there is used a helmet, or perhaps mask would be the better term. This fits right over the man's face, an air-tight joint being made between the helmet and his head by means of a rubber washer which can be inflated with air. The inflation is accomplished by squeezing a rubber ball on the right-hand side of the helmet. In the centre is a glass window through which he can see easily, and since this is apt to become clouded by the dampness of his breath there is a wiper inside, which can be turned by a knob on the outside, so that by simply turning his knob with his hand he can clean the window at any time that may be necessary. Two soft pads inside the helmet bear one on the man's forehead and the other on his chin, and these, working in conjunction with a strap which passes right round the back of his head, keep the thing firmly in position. In addition there is combined with the helmet a leather skull-cap which, being continued down behind, gives good protection to the head and neck.
The other form of apparatus consists of a mouth-piece and nose-clip. The mouth-piece, as its name implies, fits in the man's mouth, being supported and kept in position by a strap passing behind the back of his head. Combined with it is a little screw clip which closes his nostrils. The man also wears a leather skull-cap, from which straps depend tobear the weight of the mouth-piece and its attached tubes, so that the weight does not fall upon his mouth.
Either of these arrangements, it is clear, cuts him off from communication with the outer air, but that is only half the problem, for he must be given a substitute or he will be suffocated.
This part of the appliance he carries, knapsack fashion, upon his back. First there is a rectangular case, called the regenerator, with, below it, two small cylinders of compressed oxygen. A suitable arrangement of pipes connects these together, and to the helmet or mouth-piece as the case may be.
When the man exhales, as we all know, the air which he then discharges from his lungs is deficient in oxygen and instead contains carbonic acid gas. The latter must be got rid of and replaced by pure oxygen. The exhaled air is therefore led down a pipe to the regenerator, where it comes into contact with several trays of caustic soda, a chemical which has a great affinity for carbonic acid. The result is that the latter gas is extracted from the impure air, finding a more congenial home in the caustic soda. It is then necessary to restore the normal quantity of oxygen, and so, as the air passes on, it meets, in a little apparatus known as an injector, a spray of pure oxygen from the cylinders. Thus, after being purified and re-oxygenated, the air passes on through more pipes to the helmet or mouth-piece, to be breathed once more. The apparatus contains sufficient oxygen and caustic soda for this to go on for a space of two hours.
But during times of extra exertion a man needs more air than at others, for which provision has to be made, and so on his chest the rescuer carries a flexible bag divided into two compartments. Through one of these the exhaled air passes on its way to the regenerator, while through the other the oxygenated air flows on its way to the man's mouth. When he is breathing hard, then, during a moment of extra exertion, and when, therefore, he is turning out bad air faster than it can be purified, and drawing in pure air fasterthan it can be produced, this bag comes to his aid. From the store of oxygenated air in one side of it he draws the extra which he requires, while the other side stores up temporarily the excess of vitiated air, until the regenerator is able to overtake its work. Thus at all times, whether breathing ordinarily or heavily, the apparatus can respond to his demands.
The spray of oxygen as it escapes from the cylinders into the injector has the effect of driving the air along, so that the circulation through the tubes and the regenerator is automatic, and the foul air flows away from the man's mouth and the new air comes back to him quite without effort on his part. As time goes on, of course, and the stored oxygen becomes used up, the pressure in the cylinders falls, which fall, shown upon a little pressure-gauge, tells the man how much longer time he has before he must return for fresh supplies of oxygen and soda. Fresh cylinders of oxygen can be connected up very quickly in place of the empty ones, while a fresh regenerator can be put in, or new caustic soda supplied, in a very short time.
The superintendent of the Mansfield station has invented what is termed a "self-rescue" apparatus, to be used in conjunction with that which has been described above. It is simpler and lighter than the rescue apparatus, and will not keep a man supplied with air for more than an hour or an hour and a quarter. Moreover, it is not automatic, since the flow of oxygen has to be controlled by the man himself. Since, however, it consists only of a mouth-piece, a breathing-bag and a cylinder of oxygen, it is very portable, and may well be carried by a rescue party for the use of any men who may be discovered alive beyond the danger zone. It may well happen, indeed it often has happened, that a remote part of a mine, although cut off from the shaft by passages full of "after-damp," as the foul gases caused by the explosion are termed, may itself contain fairly pure air in which men can live for a long time. If such men be reached, the difficulty is to get them through the passages containing thebad air. Consequently a rescue party which carried one or two of these light forms of apparatus could equip such men with them and then they could pass out with safety.
Another use, the one, in fact, from which the appliance draws its name, is the facility with which, by its aid, a man could set right a chance defect in his ordinary rescue apparatus. Suppose, for example, that a fully equipped man found something wrong, whereby he was prevented from getting his proper supply of purified air. Then, if the party had one of the self-rescue sets with them, he could slip off his helmet or mouth-piece, quickly replacing it, for a time, with the self-rescue mouth-piece. This might enable him to reach safety, or even to put the other apparatus right and then don it once more. The whole thing can be packed up into a small tin case which can be slung over one shoulder, and with the oxygen cylinder slung over the other one the complete outfit can be carried quite easily by a man in addition to what he is wearing himself.
Still another form of breathing appliance may well be taken on these rescue expeditions, and that is the reviving apparatus, for use upon those who have apparently ceased to breathe. In this case a mask is put over the sufferer's mouth and nose, and then the turning of a lever into a certain position causes oxygen to escape from a cylinder in such a way as to cause a suction which empties the man's lungs of the bad gases which have laid him low. That done, another movement of the lever and a deep breath of oxygen flows into his lungs in their place. Thus by alternating the positions of the lever an artificial respiration is set up far more effective than can possibly be attained by the ordinary method of moving the man's arms and pressing his chest. Indeed there are cases, such as when his arms or ribs are injured, when the ordinary method is impossible, but it is hard to imagine an instance when this beneficent apparatus could not be used, and so long as there be any spark of life left in the poor fellow there seems to be every reason to expect a complete revival as the result of its use.
Of course there are many other places where poisonous gases are likely to be met with, such as gas-works, chemical-works, limeworks, and so on, where this apparatus may be kept with advantage, in case of accident.
Indeed all that has been described above has its use apart from colliery explosions, although they are the outstanding opportunities for its employment. Old workings, tunnels which have been empty for a time, sewers—all these have, on occasion, to be entered, not to mention houses full of smoke, or factories full of chemical fumes, all of which form cases in which the rescue apparatus would find useful employment.
One branch of science—medical science—concerns itself almost entirely with health, but it would be out of place to refer to such matters here, even if the present writer were capable of doing justice to the subject. A new medicine or a new method of operating upon a suffering patient would be quite correctly described as a scientific marvel, but it is not of such that this chapter deals, but rather with those great works by which the engineer, often taught by the medical man, promotes the health of a whole community.
Most important of these, perhaps, is the provision of pure water. Some places are more fortunately situated than others in this respect, being near streams flowing down from mountains clear and unpolluted, which can be drunk after the minimum of purification. Others have to make use of the waters of a moderately clean river, as London does those of the Thames and Lea, in which cases the greatest care has to be exercised in the filtration of the liquid before it can be sent out through the mains for domestic consumption.
In this particular domain invention has been comparatively slow. There are novel pumps, it is true, for handling the water, such as the Humphrey Gas Pump, which the Metropolitan Water Board (London) have installed for filling their great reservoirs at Chingford. In these an explosion of gas is the motive force. Water flows by gravitation into a huge iron pipe closed at the top but open at the bottom. It is so arranged that a quantity of gas shall be entrapped in the upper end, which, being exploded by an electric spark, drives the mass of water out. Some of it, togetherwith a quantity of fresh water, presently comes surging back, entrapping a fresh supply of gas and causing a new explosion; and so it goes on over and over again. The particular pumps at the waterworks referred to discharge about fourteen tons of water at each explosion, of which there are nine every minute.
The special effect of these machines, however, is not to improve the public health so much as to relieve the public pocket, for their chief feature is that they work more economically than any other kind of pump.
The filters, by which the water is purified, are simply layers of sand, much the same as have been in use for many years, although in some cases chemistry is brought in and the work of the filters aided by the action of precipitants. These are substances which combine in some way with the impurities in the water, and carry them to the bottom of the tank or reservoir, while the pure water remains to be drawn off from the top.
This is also the most usual method by which water is softened. Hardness in water is due to the presence of certain salts which are dissolved out of the ground as the water percolates through it, and which are absent from rain-water. To get rid of these the hard water has chemicals mixed with it in a tank, from which it flows slowly through another tank. The effect of the added chemicals is to convert the soluble salts in the water into insoluble particles, which then tend to fall down to the bottom of the containing vessel. The slow passage through the second tank is intended to give the particles time to settle.