steam goes to a feed water heater, also warmed by furnace gases, where its temperature is raised to about 170 degrees before it is returned to the boiler.

Still that does not comprise all the efforts for economy. The boiler is carefully lagged, or covered with a thick jacket of asbestos or other non-conducting material so that the loss of heat by radiation from the boiler is reduced to a negligible amount. And there's more yet. Instead of the usual locomotive type boiler so common among small-sized American steam power plants, with the bottom of the grate directly exposed to the ground so that all the heat possible can be wasted that way, the lokomobile has an internal furnace; that is, the firebox is entirely surrounded by water, except at the door. At every possible point the waste of heat is carefully guarded against.

The net result of all these precautions is that a very much smaller boiler is required to produce a given amount of

power than would be needed to yield the same amount using saturated steam. Of course the superheater costs money, SO the saving in first cost of the plant may not be very great. The saving is in operation. In an ordinary small American steam power plant, say from twenty-five to two hundred horse power, anywhere from three to five pounds of coal are required to yield one horse power for one hour. But the lokomobile only requires from 1.2 to 1.4 pounds of coal per horse power hour. It has managed to skimp along on one pound, and on one occasion, during a test run, achieved the remarkable record of 71 of a pound of coal per horse power hour. That put it far ahead of the gas producer engine which needs, on an average, one pound of coal per horse power hour. Now coal costs money, as any one who has to buy it can testify; hence, every dollar saved on the coal bill without reducing the power output is one hundred cents gained.

Another advantage of the lokomobile is that being compressed into the smallest possible space, and also because a much smaller boiler and engine are required to produce a given amount of power with superheated than with saturated steam, less money is required to provide an engine room. Again, being small for the amount of power produced one man can run a good sized plant-say up to a capacity of 250 horse poweralone. This, however, is by no means the limit of size, for lokomobile type plants are built up to a thousand horse power. The one man who runs a lokomobile being necessarily the engineer, is likely to be more competent than the average fireman, so there is still another chance to save on the coal pile. While only one man is needed to run a gas or oil engine of pretty large size, it takes an expert mechanic to adjust and repair such engines, which not infrequently require a deal of tinkering. A lesser degree of talent suffices to keep a steam engine going.

Furthermore, an internal combustion engine of any kind has a very definite limit on its capacity. A hundred horse power internal combustion engine will deliver a hundred horse power, if it feels like it, but it will do no more, no matter what inducements are held out. A steam engine, however, like a music hall artist, is always ready to oblige. If the boss happens to need a hundred and fifty horse power for an hour or two in an emergency the hundred horse power steam engine will help him out. For all these reasons a number of gas and oil engines have recently been replaced in England by superheat steam engines.

Another notable advantage which the lokomobile has over the ordinary American type steam plant of small size is the ease with which the boiler can be cleaned. The fire box and tubes are built together to form one piece and bolted to the boiler so that by unscrewing a lot of nuts the whole interior arrangements can be drawn out of the boiler shell, so that everything can be thoroughly cleaned, and then replaced. The operation of taking the boiler apart and putting it together again consumes five or six hours. Compare this with the clumsy and utterly inefficient washing which is the only way

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the small American boiler can be cleaned. The American small boiler never is really cleaned, but gradually accumulates a thickening coat of scale that renders it steadily less and less efficient. All these various things taken together enable the lokomobile with 200 degrees of superheat to deliver as much as 25 per cent more power than an engine of the same size using saturated steam and at the same time show a saving of 25 per cent in coal and 33 per cent in boiler feed water. No wonder under these circumstances that there is an enormous demand for superheat engines all over Europe and in other countries as well. Possibly these things may explain why South Americans prefer to buy their engines of European builders when they might just as well spend their money with their northern cousins.

The importance of using superheated steam in power plants, great as well as small, is now universally recognized. No fewer than five hundred steamships, most of them small, to be sure, though there are some large vessels, including warships with engines of twenty thousand horse power, are now equipped with superheaters. At sea the superheater shows a saving of 12 to 21 per cent in fuel.

Railroad men, too, begin to realize the value of the superheater. There are now more than twelve thousand locomotives in the world equipped with superheaters, of which more than two thousand are in the United States. On the railroad the superheater effects a saving of about 25 per cent in fuel under average working conditions. This really amounts to an increase of 33 per cent in the capacity of the locomotive. To illustrate: A locomotive burning six thousand pounds of coal per hour and developing fifteen hundred horse power would, if equipped with a superheater, produce the same amount of power from forty-five hundred pounds. But being capable of turning six thousand pounds of coal into effective energy in an hour, if that amount is now consumed the power output will be increased to two thousand horse power-a gain of 33 per cent.

It is only the small consumer of steam, the man who most needs to be saving, who does not obtain all the economies modern engineering can supply.

A

ure

MERE twenty-five, fifty or seventy-five feet deeper in the shadowy ocean depths than divers can now go lies treas- treasure of gold and treasure of knowledge-that has set the minds of men afire for ages. Within the cast of a bass-lure, if it were but on the surface, from where the deep-sea worker reaches his deadline, sunken argosies and strange new forms of life lie side by side, yet out of reach.

If a false floor existed in the ocean depths about one hundred and ninety feet. from the surface, things lying deeper could not be more hopelessly out of the grasp of the diving human being than they have been in the past. One hundred and ninety feet has been the outside limit of the deepest plunging our bodies would stand, because old ocean would squeeze the life out of us if we went deeper. The human body will endure only about so much pressure, and pressure is the ocean's specialty in those mysterious deeps.

Four Englishmen have recently come forward to declare, however, that our notions of what we can stand have been too modest. They are authoritative fellows, tooDr. Leonard Hill and Mr. Greenwood, of the London Hospital medical school, Prof. J. S. Haldane and Surgeon Oswald Rees, of the British navy. They say that the diver can and shall go-has gone, in factmore than twice the distance mentioned into the waters of the sea. They tell us that we can have the treasures of which we have been despairing, if we will

but undertake to go after them right— or rather, if we will undertake to return with sufficient care, after the trip. And they support their statements by records of long experiments and by actual experiences of their own.

Nearly everybody who has read the magazines and newspapers in recent years has heard of a strange disease, called the "bends," to which men are subject who work under great air pressures the fellows, particularly, who go down into the caissons for deep tunnelwork, where compressed air has to be used to keep water or mud from coming in upon them to drown them. "Sandhogs" and divers alike have been the victims of the malady, which no one has very clearly understood. Physicians and other scientists have long studied it and treated it with varying success. Men afflicted with it show symptoms of asphyxiation, paralysis and other equally serious things, sometimes resulting in death, often in permanent injury.

Now the investigating Englishmen have found out what causes the "bends."

And in that discovery lies the secret of the new diving-power they promise us. It is a pretty common habit of human beings to breathe air into the lungs, and one that the race has never been able, as yet, to shake off. The air we breathe is under pressure, normally, at sea level, of about fifteen pounds to the square inch. At a depth of one hundred feet under water, there is a pressure of fortyfour pounds to be added to this, when the diver tries to reach the low levels. That makes a pressure of fifty

nine pounds, to the square inch of body surface, that he must resist. At a depth of four hundred feet under water, the pressure reaches the enormous figure of one hundred and ninety-one pounds per inch-which would be high pressure for a locomotive's boiler to contain in regular work. Hence, when men have essayed to drop down to these depths, they have found conditions that they were not prepared to meet. Curiously enough, however, like the Irishman who complained that it was not the falling that hurt him but "the stopping so quick," so it has not been the diving into high pressures that has cost divers their lives or their health, but the coming up too rapidly. This

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pounds pressure, with slight variations, according to our elevation above sealevel, it behaves very well. Under great pressure, as in the caissons or under water, it acts quite differently. Instead of passing peaceably out of the system as it normally should, it starts a sort of game of hide and seek through the bloodchannels, running

has been understood in a general way, for some time. In the caissons, where the sand-hog works, there are air-locks, through which, by easy stages, a man ascends from the depths and through slowly lessening pressures, till he reaches the surface. The deep-sea divers have observed something of the same formula in rising to the surface of the ocean, coming up by slow and careful degrees. But, even with the greatest care and the most intelligent assistance, the men who have risked themselves in this class of work have suffered terribly and mysteriously from the disease which seemed to be a very ally of the sea to prevent our uncovering its secrets.

Now, the "bends" is a strange malady, that has baffled everybody till the four Englishmen determined to solve the problem it offered. It is caused by the very air in the body of the man who contracts it. When we breathe, we take into our lungs a combination of oxygen and nitrogen, of which the blood takes the former, for cleansing and fuel purposes. About eighty per cent of the air, roughly, however, is nitrogen. And it is the nitrogen that causes the "bends." Under sixteen

off in bubbles into the smaller arteries and veins and the capillaries, and staying there, much to the detriment of normal functions in those parts. It is forced out of its regular course of progress by the pressure under which it is breathed, and crowded off into places where it does not belong. Of course, it makes trouble.

A man's body is a compressible thing. The tissues are soft and capable of receiving the nitrogen under pressure-not only capable of receiving, but incapable of resisting. When the diver reaches a point under water where the pressure becomes high enough to force the nitrogen off into the capillaries in his body, he becomes a fit subject for the "bends,' and the only way to save him is to bring him back to the surface so slowly that the nitrogen, which moves slowly in the tiny blood-passages, can have time to get out of them again, before the high pressure is entirely removed. If he comes up too quickly, the nitrogen remains in the tissues and he becomes asphyxiated or paralyzed, or something else happens to him that is both painful and incapacitating, if not actually killing.

Professor Haldane and Surgeon Rees experimented with the usual animals, submerging them and bringing them up to the surface with every conceivable variety of method and speed. The guineapigs and dogs and goats that were used showed all varieties of the disease that men had been suffering from. They had the "bends" as truly as any sand-hog that

ever came up too quickly out of the airlocks. But, patiently changing conditions and watching results, the experimenters made a discovery. They found that if time enough were taken in the course of return from high to low air pressures, no "bends" appeared. Then they found that depths could be increased and pressures raised very materially, if the return to the surface were correspondingly slow. And then, to crown the whole, they learned that the stage of the return in which it is really necessary to take time and care, is not the first stage-from the deepest to the less deep depths, from the highest to the medium pressures -but in the later stages, in the change from the medium pressures to the normal, at the surface.

of the Scottish coast was chosen for the place of trial, and there these courageous men went down to depths of thirty-five fathoms-two hundred and ten feet-and actually stayed there and worked as no diver has ever attempted to do at much lesser depths. More than that they descended and ascended at greater speeds,

When they had found out these things, they began a truly remarkable series of feats. First they showed that a goat could stand pressures that no man had ever endured and lived, up to that time. Most divers who have approached a depth of one hundred and ninety feet, have, sooner or later, paid dearly for their temerity. When the goat experiments were ended, however, Mr. Greenwood submitted to air-pressure, in a specially prepared tank, in a degree equal to that at a depth of two hundred and six feet, and suffered no ill effects. Moreover, he remained in that pressure for a much longer time than any diver had ever stayed at deep-sea levels. And when he came out of that tank, a new leaf in Nature's endless book of knowledge had been turned.

Professor Haldane and Surgeon Rees followed Mr. Greenwood with other experiments, in which they were the subjects, and their experiences duplicated his. It remained then to put the results to practical application in diver's dress

observing only their newly discovered principle of making the last stage of the ascent slowly; and they felt no ill effects of any account whatever.

They established the fact that divers can go down to the depth of thirty-five fathoms in the astoundingly quick time of two minutes, while, previously, the interval prescribed for anything like similar depths has been close to forty minutes! They found that it is perfectly safe to ascend rapidly from thirty-five fathoms to twelve fathoms, thus getting out of the danger-zone of high pressure quickly, and thence to come to the surface more gradually, without resultant suffering. During the mounting of the last twelve fathoms of distance, the body frees itself of all excess nitrogen.

This is contrary to all accepted methods held as absolute heretofore. But the English scientists have established their discoveries as facts by long continued and often repeated demonstrations. More, they have shown by experiments with animals, that the four-hundred-foot depth can be reached with equal safety. And, now, with their power of endurance practically doubled, the divers of the world can delve after the secrets and the treasures of the ocean's bottom in a way that was only dreamed of before, and can bring up lost and undiscovered things that have tantalized us since ships began to sink and strange forms of unknown life began to wash up upon our shores with every visit of the frequent storm