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face by the erosion of running surface waters, for most of them occur in valleys (as in the illustration) and not on heights.

Such a deposit as this first one is shallow, and ordinarily has little pressure behind it to force it up and comparatively little oil to be forced up. Usually it is of little value. The illustration shows no derricks on the hills back of it, thus indicating that it is not being worked.

The second of the three deposits is much like the first, except that it has not yet reached the surface-or that the surface has not yet been cut down to it. Nevertheless, the strata between which it lies apparently continue their slanting course to the surface; and as it has pressure beneath it and as the contact between two different strata is likely to be a plane of weakness the oil is probably being forced very slowly upward between them. No gas, which to some extent accompanies all oil deposits, is shown in the illustration, indicating that any that was once there has filtered through the rocks (probably along the strata contact) and has escaped into the air. However, this gas might very well have been drawn off through the many wells whose derricks are shown on the hills in the background. (Most of these appear to tap this second deposit, but the wells themselves cannot be shown in the model, for they are too far in the background.)

The third deposit (on the left) differs markedly from the other two. The strata between which it has been forced surfaceward evidently do not continue on the same slant to the surface. Instead, they curl over and begin to trend downward, forming an "anticline," which traps the gas and the oil, permits neither of them to reach the surface, and compels both to form an accumulation, known as a "pool." (This pool is cut off in the model by a slanting dotted line, which would, of course, never occur in nature; everything to the left of this line belongs to another model.)

"Anticlinal" pools are ordinarily the most valuable of all. Most of them are topped by a gas pool (shown in white in the illustration), which may be valuable; and practically all of them have much pressure behind them to force them, through any well that may tap them, to the surface of the ground, perhaps as a "gusher."

The pressure behind all oil deposits comes from water, which, from its mode of occurrence, is called "artesian." The principle

is simple: If water is poured into one arm of a tube curved like the letter U, it will, of course, rise in the other arm to the same height. If the other arm is sealed, say halfway down, so that the water cannot rise, it will press against the seal. Ordinarily, it will trap a little air between it and the seal. And if the water contains anything that is lighter than itself, say oil, this oil will in time rise and accumulate on the surface of the water just below the trapped air. If, now, a hole is poked in the seal, the air will first be forced out by the pressure beneath; the floating oil will come next; and the water last.

Exactly so is it in an oil deposit, except that instead of being confined in a tube, the oil, etc., is confined in a curved sheet lying between two layers of rock. The water is "poured in" by rain, which falls and sinks in on higher ground miles and miles away; and if this source is high enough, the pressure at the other side of the. "U" will be great, particularly if the air (gas), oil, and water are trapped by an anticline. And when the anticline is pierced by a well, gas, oil, and water will be forced out in turn. When the water begins to come, the well is done for. CRITTENDEN MARRIOTT.

THE HEAT EYE

THE war of yesterday was disastrous enough in its effect upon nations, but the war of tomorrow, with its added devices of destruction, products of the minds of our scientists and inventors, may destroy civilization itself. "The Heat Eye" is one example of the perfecting of war's mechanism, and presented, as it is, in November, the month of the disarmament conference in Washington, may serve as a further object lesson, and a warning, too, that unless we limit our armaments and discourage preparation for war, we may be destroyed by our own inventive genius.

Boys and girls of to-day are so familiar with radio-telegraphy and the idea of electromagnetic waves radiating through the ether that it is not as difficult for them to conceive of light as a wave action as it used to be for the boys and girls of the previous generation. However, it is just as astounding to-day as it ever was to learn that the vibrations must run as high as 450 trillion (450,000,000,000,000) per second before the eye will take the slightest notice of them! The eye will then see them as a dull red glow. As the rate of vibration increases, the color of the light changes

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THE NEW INSTRUMENT THAT DETECTS OBJECTS IN THE DARK BY THEIR BODILY HEAT

through all the hues of the rainbow until, at the violet end of the rainbow, where the vibrations run up above 700 trillion, the eye is no longer able to see any light. Just as our ears are deaf to vibrations below 32 per second and above 36,000 per second, so our eyes, which are infinitely more sensitive, are blind to vibrations below 450 trillion and above 700 trillion per second. In fact, our range of vision is very limited indeed.

There are rays beyond the range of the eye. Those below the red are known as infra-red rays, and those beyond the other end of the spectrum as the ultra-violet. The infra-red rays are heat rays, which we can feel, but not see. Every body that is warmer than its surroundings is radiating these rays. They are very similar to the visible light waves. They travel in straight lines and can be reflected and refracted, but they will not go through glass; in fact, there are few substances that are transparent to heat rays, one of the notable exceptions being rock-salt. While glass lenses cannot be used to focus the rays, a concave mirror may be used to gather the

rays that fall upon it and bring them to a focus. With such mirrors, very delicate heat measurements have been made, such as the heat of the moon and of the distant stars.

During the Great War, each side turned to its scientists for help in solving the many problems that came up. In previous wars, the fighting had usually been confined to the daylight hours, and seldom were there any night battles, because of the difficulty of distinguishing friend from foe. But in the World War, particularly after the conflict had settled down to trench warfare, the battles went on day and night; in fact, the activity was greater when concealed by the cloak of darkness. How to put a stop to night raids, scouting, and other operations proved a baffling problem. Flares were used to illuminate "No-Man's-Land," and star-shells, that threw out brilliant candles suspended from parachutes so that they would settle slowly to the ground. But these lights were not adequate. The enemy would drop to the ground and remain motionless while the light was burning, only to resume

operations when all was dark again. Something better than an occasional flare was needed to put a stop to these night activities.

It was not until the closing months of the war that the answer was found and an instrument made that would see the enemy in the dark. By the time the instrument was ready for actual service at the front, the German lines had begun to give way and night raids were no longer a menace, but the possibilities of the instrument were demonstrated thoroughly before it was sent to the trenches.

The new instrument detected objects by their bodily heat. Every warm-blooded animal radiates heat. You can prove it by putting a cold hand close to your warm cheek, when you will feel the radiation of heat from your face. If our eyes were built to see heat rays below the red end of the spectrum, men and animals would glow at night with a reddish light. Obviously, under such conditions, night raids would be impracticable. The problem, then, was to make an artificial eye that would be sensitive to radiant heat, and then, no matter how black the night, the enemy could not escape the gaze of this heat eye.

As shown in the drawing, the apparatus was composed of two parts, one consisting of a 24-inch parabolic mirror with a highly sensitive thermopile at the focus of the mirror, and the other of a very delicate galvanometer, with which the slight electric currents produced by the play of heat rays on the thermopile were detected.

For the benefit of those who are not familiar with the thermopile, we must explain the nature of that apparatus. When two strips of metal that have widely different electrical properties are joined at one end and heated at the joint, an electrical stress is set up which results in a flow of current, if the circuit is completed by connecting the opposite ends of the strips. While one couple of strips gives a weak current of very low voltage, a number may be connected in series to build up the voltage to an appreciable amount.

The inset in our drawing shows the type of thermopile that was used. It consisted of fine hairlike wires of bismuth and of silver soldered together in couples which were connected in series. This furnished an exceedingly sensitive thermopile, which had to be handled very carefully and protected from the slightest changes of temperature. The hairlike wires were stretched across a narrow slit in a porcelain block, which in turn was mounted in a heavy metal holder with the

wires on the inner side. A metal coverplate was fastened over the holder, and in this lid was a window of rock-salt that registered with the slot in the porcelain block. A thin coat of varnish protected the rock-salt window from moisture. The thermopile was set up in the focus of the mirror, so that the heat waves passed through the salt window and slot to the wires. The slightest variation of heat generated an electric current, which was indicated by the galvanometer.

With this instrument, men were easily detected at a distance of 600 feet. In one test a man lay in a shell-hole in the ground 400 feet away from the instrument. Every time he raised his head above ground, the galvanometer recorded the fact.

Our drawing shows how the instrument might have been used in the war. Had it been set in an advance post in front of the trenches, it could have been trained parallel to the trenches. None of the enemy could have crossed the "line of sight" of this heat eye without detection. No surprise attacks could have been staged, and, warned by the man at the galvanometer, the defenders could have lighted up the scene with flares and star-shells. A pair of these instruments could have been used to get the exact range of a lurking enemy, and he could have been destroyed without the aid of a light.

It so happened that when the German lines began to crack, airplane warfare increased, and there was a call for an instrument that would locate aërial bombers with accuracy. Sound-ranging instruments were not satisfactory because of lag. A machine could travel a considerable distance while the sound was traveling from the machine to the earth. Heat rays, on the other hand, travel with virtually the same speed as light. Evidently, a thermopile detector could be trained directly on the airplane, although the night were pitch black, and the gunners could be given an accurate range. Accordingly, a larger thermopile was constructed, and with it aircraft could be picked up with ease a mile away. However, the war was ended two months before the machine was completed and ready for service. A. RUSSELL BOND.

THE CONSTELLATIONS FOR NOVEMBER DIRECTLY South of Cassipoeia and Cepheus, the far northern constellations with which we became acquainted last month, and almost overhead in our latitudes in the early evening hours of November, lie Pegasus, The

Winged Horse, and Andromeda, The Woman Chained.

According to the legend, Cepheus was king of Ethiopia, and Cassiopeia, his beautiful, but vain, queen who dared to compare herself in beauty with the sea-nymphs. This so enraged the nymphs that, as a punishment for her presumption, they decided to send a terrible sea-monster to ravage the coast of the kingdom. The king and queen, upon consulting the oracle, found that the only way to avert this calamity would be to chain their daughter Andromeda to the rocks and permit the monster to devour her.

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chanced to be riding through the air on his winged horse and saw, far beneath him, the beautiful maiden chained to the rocks and the frightful monster approaching to devour her. He immediately went to the rescue, and, after a terrible struggle with the monster, succeeded in overpowering him and thus saved the maiden from a dreadful fate. seus and the fair Andromeda were married shortly afterward, and at the end of a happy life the pair were transferred to the heavens. Cassiopeia, the vain queen, was ordered to be bound to a chair and, with the king Cepheus at her side, to be swung continually around the north pole of the heavens that she might be taught a lesson in humility.

The constellation, Cetus, representing the sea-monster, may be found to the southeast and south of Pisces, The Fishes, which lie south of Andromeda and Pegasus.

The Great Square in Pegasus, which is outlined by the four principal stars in the constellation, is the most conspicuous configuration of stars to be seen in the heavens in autumn evenings. The star that marks the northeastern corner of The Great Square belongs to the constellation of Andromeda and marks the head of the maiden, who is resting upon the shoulders of Pegasus, The Winged

Horse. The three bright stars nearly in a straight line outline the maiden's body, Alpha, or Alpheratz, as it is also called, being the star in the head, Beta or Mirach in the waist, and Gamma or Almach in the left foot. The last-named star, which is farthest to the northeast in the diagram, was, in the opinion of the noted astronomer Herschel, the finest double star in the heavens. The two stars into which the telescope splits it are of the beautifully contrasted shades of orange and

sea-green.

A second most interesting object in Andromeda and one of the finest in the entire heavens is The Great Andromeda Nebula, which is faintly visible without the aid of a telescope as a hazy patch of light. It is believed that in reality this nebula is a great universe composed of many thousands of stars so distant that no telescope can show the individual members, the impression brought to our eyes being that of their combined light. Within the past few years, eleven very faint temporary stars stars that flare up to sudden brightness and then fade rapidly from viewhave been detected within the bounds of this great nebula, and this has strengthened astronomers in their belief that this small patch of misty light is a great universe of suns, similar to our Milky Way, at a distance from the earth so great that the light from it N

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objects that the human eye fails to see.

a clear dark evening one may find the Great Andromeda Nebula by the aid of two faint stars with which it makes a small triangle, as shown in the chart. This nebula is the only one of the class of spiral nebulas to which it belongs that can be seen in these latitudes without the aid of a telescope, though there are several spiral nebulas in the southern heavens that can be so found.

Lying to the northwest of the Great Square in Pegasus are a number of faint stars that represent the shoulders and head of the winged steed, while the stars to the southwest of the square outline his fore legs. The creature is represented without hind quarters in all star atlases. The space within the Great Square contains no bright stars, and as a result, the outline of the square stands out very distinctly. There are, in fact, no stars of the first magnitude in either Pegasus or Andromeda, though there are a number of the second and third magnitude which very clearly outline the distinctive form of these two star-groups.

Pisces, The Fishes, the constellation just south of Andromeda and Pegasus, is the first of the twelve zodiacal constellations that lie in the path of the sun, moon, and planets. It consists of the southern fish, lying in an east-to-west direction, and the northern fish, lying nearly north and south, the two touching at the southeastern extremity of the constellation.

There is in Pisces not a single bright star, and its only point of interest is to be found in the fact that it contains the point, marked by the cross and letter V in the diagram, that is known variously as "the vernal equinox," "the equinoctial point" and "The First Point in Aries." This is a very important point of reference in the heavens, just as the meridian of Greenwich is for the earth, and it marks the point where the sun crosses the equator going north in the spring. Owing to the "precession of the equinoxes," as it is called, this point is gradually shifting its position westward through the zodiacal constellations at a rate that will carry it completely around the heavens through the twelve zodiacal groups in a period of 25,800 years. Since the Since the beginning of the Christian Era, this point has backed from the constellation of Aries, which lies just east of Pisces, into Pisces, though it retains its name of "The First Point in Aries."

None of the five bright planets that are visible without the aid of the telescope will appear in the evening sky this month. The

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EXAMINING THE RESULT AFTER TWO SHOTS

"Almost the only drawback to these good qualities of glass is its brittleness." But this objection has now been overcome and an unbreakable glass has been produced.

The safety glass, as it is called, looks exactly like, and possesses all the qualities of, the old-fashioned glass, only it is not brittle. Quite the contrary, it has more the qualities of a plate of steel than a pane of glass. It is of two kinds, the "bullet-proof" and the "unbreakable." So serious did the menace of flying glass in connection with automobile smash-ups become, that several years ago two New York policemen, Commissioner Joseph A. Faurot and Officer Clinton L.

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