CHAPTER XV

THE AEROPLANE IN THE GREAT WAR

DURING the civil war the Federal forces used captive balloons for the purpose of discovering the positions of the enemy. They were of great service at that time, although they were stationed far within the lines to prevent hostile guns from reaching them.

BALLOON OBSERVATIONS.--Necessarily, observations from balloons were and are imperfect. It was found to be very unsatisfactory during the Russian-Japanese war, because the angle of vision is very low, and, furthermore, at such distances the movements, or even the location of troops is not observable, except under the most favorable conditions.

Balloon observation during the progress of a battle is absolutely useless, because the smoke from the firing line is, necessarily, between the balloon and the enemy, so that the aerial scout has no opportunity to make any observations, even in detached portions of the fighting zone, which are of any value to the commanders.

CHANGED CONDITIONS OF WARFARE.--Since our great war, conditions pertaining to guns have been revolutionized. Now the ranges are so great that captive balloons would have to be located far in the rear, and at such a great distance from the firing line that even the best field glasses would be useless.

The science of war has also evolved another condition. Soldiers are no longer exposed during artillery attacks. Uniforms are made to imitate natural objects. The khaki suits were designed to imitate the yellow veldts of South Africa; the gray-green garments of the German forces are designed to simulate the green fields of the north.

THE EFFORT TO CONCEAL COMBATANTS.--The French have

discarded the historic red trousers, and the elimination of lace, white gloves, and other telltale insignias of the officers, have been dispensed with by special orders.

In the great European war armies have burrowed in the earth along battle lines hundreds of miles in length; made covered trenches; prepared

artificial groves to conceal batteries, and in many ingenious ways endeavored to make the battlefield an imitation field of nature.

SMOKELESS POWDER.--While smokeless powder has been utilized to still further hide a fighting force, it has, in a measure, uncovered itself, as the battlefield is not now, as in olden times, overspread with masses of rolling smoke.

Nevertheless, over every battlefield there is a haze which can be penetrated only from above, hence the possibilities of utilizing the aeroplane in war became the most important study with all nations, as soon as flying became an accomplished fact.

INVENTIONS TO ATTACK AERIAL CRAFT.--Before any nation

had the opportunity to make an actual test on the battlefield, inventors were at work to devise a means whereby an aerial foe could be met. In a measure the aerial gun has been successful, but months of war has shown that the aeroplane is one of the strongest arms of the service in actual warfare.

It was assumed prior to the European war that the chief function of the aeroplane would be the dropping of bombs,--that is for service in attacking a foe. Actual practice has not justified this theory. In some places the appearance of the aeroplane has caused terror, but it has been found the great value is its scouting advantages.

FUNCTION OF THE AEROPLANE IN WAR.--While bomb throwing may in the future be perfected, it is not at all an easy problem for an aviator to do work which is commensurate with the risk involved. The range is generally too great; the necessity of swift movement in the machine too speedy to assure accuracy, and to attack a foe at haphazard points can never be effectual. Even the slowly-moving gas fields, like the Zeppelin, cannot deliver bombs with any degree of precision or accuracy.

BOMB-THROWING TESTS.--It is interesting, however, to understand how an aviator knows where or when to drop the bomb from a swiftly-moving machine. Several things must be taken into consideration, such as the height of the machine from the earth; its speed, and the parabolic curve that the bomb will take on its flight to the earth.

When an object is released from a moving machine it will follow the

machine from which it is dropped, gradually receding from it, as it descends, so that the machine is actually beyond the place where the bomb strikes the earth, due to the retarding motion of the atmosphere against the missile.

The diagram Fig. 90 will aid the boy in grasping the situation. A is the airship; B the path of its flight; a the course of the bomb after it leaves the airship; and D the earth. The question is how to determine the proper movement when to release the bomb.

METHOD FOR DETERMINING MOVEMENT OF A BOMB.--Lieut.

Scott, U. S. A., of the Coast Survey Artillery, suggested a method for determining these questions. It was necessary to ascertain, first, the altitude and speed. While the barometer is used to determine altitudes, it is obvious that speed is a matter much more difficult to ascertain, owing to the wind movements, which in all cases make it difficult for a flier to determine, even with instruments which have been devised for the purpose.

_Fig. 90. Course of a Bomb._

Instead, therefore, of relying on the barometer, the ship is equipped with a telescope which may be instantly set at an angle of 45 degrees, or vertically.

Thus, Fig 91 shows a ship A, on which is mounted a telescope B, at an angle of 45 degrees. The observer first notes the object along the line of 45 degrees, and starts the time of this observation by a stop watch.

The telescope is then turned so it is vertical, as at C, and the observer watches through the telescope until the machine passes directly over the object, when the watch is stopped, to indicate the time between the two observations.

_Fig. 91. Determining Altitude and Speed._

The height of the machine along the line D is thus equal to the line E from B to C, and the time of the flight from B to a being thus known, as well as the height of the machine, the observer consults specially-prepared tables which show just what kind of a curve the bomb will make at that height and speed.

All that is necessary now is to set the sighter of the telescope at the

angle given in the tables, and when the object to be hit appears at the sight, the bomb is dropped.

THE GREAT EXTENT OF MODERN BATTLE LINES.-- The great

war brought into the field such stupendous masses of men that the battle lines have extended over an unbroken front of over 200 miles.

In the battle of Waterloo, about 140,000 men were engaged on both sides, and the battle front was less than six miles. There were, thus massed, along the front, over 20,000 men every mile of the way, or 10,000 on each side.

In the conflict between the Allies and the Germans it is estimated that there were less than 7500 along each mile. It was predicted in the earlier stages of the war that it would be an easy matter for either side to suddenly mass such an overwhelming force at one point as to enable the attacking party to go through the opposing force like a wedge.

Such tactics were often employed by Napoleon and other great masters of war; but in every effort where it has been attempted in the present conflict, it was foiled.

The opposing force was ready to meet the attack with equal or superior numbers. The eye of the army, the aeroplane, detected the movements in every instance.

THE AEROPLANE DETECTING THE MOVEMENTS OF

ARMIES.--In the early stages of the war, when the Germans drove the left of the French army towards Paris, the world expected an investment of that city. Suddenly, and for no apparent reason, the German right was forced back and commenced to retreat.

It was not known until weeks afterwards that the French had assembled a large army to the west and northwest of Paris, ready to take the Germans in flank the moment an attempt should be made to encircle the Paris forts.

The German aviators, flying over Paris, discovered the hidden army, and it is well they did so, for it is certain if they had surrounded the outlying forts, it would have been an easy matter for the concealed forces to destroy their communications, and probably have forced the surrender of a large part of the besiegers.

The aeroplane in warfare, therefore, has constantly noted every disposition of troops, located the positions and judged the destination of convoys; the battery emplacements; and the direction in which large forces have been moved from one part of the line to the other, thus keeping the commanders so well informed that few surprises were possible.

THE EFFECTIVE HEIGHT FOR SCOUTING.--It has been shown

that aeroplane scouting is not effective at high altitudes. It is not difficult for aviators to reach and maintain altitudes of five thousand feet and over, but at that elevation it is impossible to distinguish anything but the movement of large forces.

SIZES OF OBJECTS AT GREAT DISTANCES.--At a distance of one mile an automobile, twenty feet in length, is about as large as a piece of pencil one inch long, viewed at a distance of thirty-five feet. A company of one hundred men, which in marching order, say four abreast, occupies a space of eight by one hundred feet, looks to the aviator about as large as an object one inch in length, four and a half feet from the eye.

The march of such a body of men, viewed at that distance, is so small as almost to be imperceptible to the eye of an observer at rest. How much more difficult it is to distinguish a movement if the observer is in a rapidly-moving machine.

For these reasons observations must be made at altitudes of less than a mile, and the hazard of these enterprises is, therefore, very great, since the successful scout must bring himself within range of specially designed guns, which are effective at a range of 3000 yards or more, knowing that his only hope of safety lies in the chance that the rapidly-moving machine will avoid the rain of bullets that try to seek him out.

SOME DARING FEATS IN WAR.--It would be impossible to recount the many remarkable aerial fights which have taken place in the great war. Some of them seem to be unreal, so startling are the tales that have been told. We may well imagine the bravery that will nerve men to fight thousands of feet above the earth.

One of the most thrilling combats took place between a Russian aeroplane and a Zeppelin, over Russian Poland, at the time of the first German invasion. The Zeppelin was soaring over the Russian position, at

an altitude of about a mile. A Russian aviator ascended and after circling about, so as to gain a position higher than the airship, darted down, and crashed into the great gas field.

The aviator knew that it meant death to him, but his devotion led him to make the sacrifice. The Zeppelin, broken in two, and robbed of its gas, slowly moved toward the earth, then gradually increased the speed of its descent, as the aeroplane clung to its shattered hulk, and by the time it neared the earth its velocity was great enough to assure the destruction of all on board, while the ship itself was crushed to atoms.

One of the most spectacular fights of the war occurred outside Paris, when one of the German Taubes attempted to make its periodical tour of observation. One of the French aeroplanes, which had the advantage of greater speed, mounted to a greater altitude, and circled about the Taube.

The latter with its machine gun made a furious attack, during these maneuvers, but the French ship did not reply until it was at such an elevation that it could deliver the attack from above. Then its machine gun was brought into play. As was afterwards discovered, the wings and body of the Taube were completely riddled, and it was a marvel how it was possible for the German aviator to remain afloat as long as he did.

Soon the Taube was noticed to lurch from side to side, and then dart downwardly. The monoplane, in the pursuit, gradually descended, but it was not able to follow the destroyed Taube to the earth, as the latter finally turned over, and went swirling to destruction.

The observer, as well as the aviator, had both been killed by the fire from the monoplane.

In the trenches on the Marne, to the northeast of Paris, where the most stubborn conflict raged for over a week, the air was never clear of aeroplanes. They could be seen in all directions, and almost all types of machines were represented. The principal ones, however, were monoplanes.

THE GERMAN TAUBE.--The German Taube is a monoplane, its main supporting surfaces, as well as the tail planes, are so constructed that they represent a bird. Taube means dove. It would have been more appropriate to call it a hawk.

On the other hand, the French monoplane, of which the Bleriot is the best known example, has wings with well rounded extremities, and flaring tail, so that the two can be readily distinguished.

On one occasion, during the lull in the battle, two of the Taubes approached the area above the French lines, and after ascending to a great height, began the volplane toward their own lines. Such a maneuver was found to be the most advantageous, as it gave the scouting aeroplane the advantage of being able to discover the positions and movements with greater ease, and at the same time, in case of accident to the machine, the impetus of the flight would be to their own lines.

Three of the French aeroplanes at once began their circling flight, mounting higher and higher, but without attempting to go near the Taubes. When the French ships had gained the proper altitude, they closed in toward the German ships, before the latter could reach their own lines in their volplaning act.

This meant that they must retreat or fight, and the crack of the guns showed that it meant a struggle. The monoplanes circled about with incredible skill, pouring forth shot after shot. Soon one of the Taubes was seen to flutter. This was the signal for a more concentrated attack on her.

The army in the trenches, and on the fields below, witnessed the novel combat. The flying ships were now approaching the earth, but the gunners below dared not use their guns, because in the maneuvers they would be as likely to strike friend as foe.

The wounded Taube was now shooting to the earth, and the two monoplanes began to give their attention to the other ship, which was attempting to escape to the north. The flash of the guns of all the fliers could be plainly seen, but the sounds were drowned by the roar of the great conflict all about them.

The Taube could not escape the net around her. She, too, was doomed. A shot seemed to strike the gasoline tank, and the framework was soon enveloped in flames. Then she turned sidewise, as the material on one side burned away, and skidding to the left she darted to the earth, a shapeless mass.

It was found that the aviator was not hurt by the shot, but was,

undoubtedly, killed by the impact with the earth. The observer was riddled with bullets, and was likely dead before the ship reached the earth.

In the western confines of Belgium, near Ypres, the British employed numerous aircraft, many of them biplanes, and at all times they were in the air, reporting observations. Many of the flying fights have been recorded, and the reports when published will be most thrilling reading.

HOW AEROPLANES REPORT OBSERVATIONS.--It may be of

some interest to know how aeroplanes are able to report observations to the commanders in the field, from the airship itself. Many ingenious devices have been devised for this purpose.

SIGNAL FLAGS.--The best known and most universally used method is by the use of signaling flags. Suppose the commander of a force is desirous of getting the range of a hidden battery, or a massed force in his front. The observer in the aeroplane will sail over the area at an understood altitude, say one mile in height.

The officer in charge of the battery, knowing the height of the airship, is able, by means of the angle thus given him, to get the distance between his battery and the concealed point beneath the airship. The observer in the airship, of course, signals the engineer officer, the exact point or time when the airship is directly above, and this gives him the correct angle.

The guns of the battery are then directed and fired so as to reach the concealed point. It is now important to be able to send intelligible signals to the officer in charge of the battery. If the shot goes beyond the mark, the observer in the airship raises the flag above his head, which indicates that it was too high.

HOW USED.--If the shot fell short he would lower the flag. If the shot landed too far to the right, this would be indicated by the flag, and if too far to the left, the signal would, in like manner, be sufficient to enable the gunners to correct the guns.

When the exact range is obtained the observer in the ship waves the flag about his head, in token of approval. All this work of noting the effect of the shots must be taken while the airship is under fire, and while circling about within visual range of the concealed object below.

The officer in charge of the battery, as well as the observer on the

flying craft, must be equipped with powerful glasses, so the effect of the shots may be noted on the one hand, and the signals properly read by the officer on the other hand.

It may be said, however, that air battles have not been frequent and that they have been merely incidents of the conditions under which they were operated. The mission of the aeroplane is now conceded to be purely one of observation, such as we have described.

Both French and German reports are full of incidents showing the value of observations, and also concerning the effects of bombs. Extracts from the diaries of prisoners gave many interesting features of the results of aeroplane work.

CASUALTIES DUE TO AEROPLANES.--In the diary of one was found the remark: "I was lucky to escape the bomb thrown by a French aviator at Conrobet, which killed eight of my companions."

Another says: "The Seventh Company of the Third Regiment of the Guard had eight killed and twenty-two wounded by bomb from a French aeroplane."

Another: "An officer showed us a torn coat taken from one of sixty soldiers wounded by a bomb from an aeroplane."

A prisoner says: "Near Neuville an aeroplane bomb dropped on a supply train, killed four men, wounded six, and killed a considerable number of horses."

The Belgians, after their defeat and the capture of Antwerp, were forced to the west along the coast. In some way they learned that the Kaiser was about to occupy a chateau near Dixmunde. Several aviators flew above the position and dropped a number of bombs on the building, completely wrecking it, and it was fortunate that the Emperor left the building only twenty minutes before, as several of his aides and soldiers on duty were killed.

On numerous occasions the headquarters of the different commanders have been discovered and had to be moved to safer places.

During all these wonderful exploits which will live in history because men had the opportunity during the war to use them for the first time in actual conflict, the official reports have not mentioned the aviators by

name. The deaths of the brave men have brought forth the acknowledgments of their services. During the first three months of the war it is estimated that over sixty aviators and aides had lost their lives in the conflict on the two great battle lines. This does not take into account those who met death on the Zeppelins, of which five had been destroyed during that time.

THE END

GLOSSARY OF WORDS USED IN TEXT OF THIS VOLUME

Where a word has various meanings, that definition is given which will express the terms used by the author in explaining the mechanism or subject to which it refers.

Aviation. The art of flying.

Altitude. Height; a vertical distance above any point. Attraction. The art or process of drawing towards.

Allusion. Referring to a certain thing. Assume. Taking it for granted.

Accentuated. To lay great stress upon a thing.

Angle of Movement. Any direction which is upwardly or downwardly, as distinguished from the direction of movement which is either to the right or to the left.

Acquire. To obtain; to recover; to procure.

Analogous. Corresponding to or resembling some other thing or object.

Air Hole. A term used to express a condition in flying where the machine while in horizontal flight takes a sudden drop, due to counter currents.

Ailerons. Literally, small planes. Used to designate the small planes which are designed to stabilize a machine.

Angle. A figure, or two straight lines which start at the same point. The sides of these lines are termed the angle.

Analysis. To separate; to take apart and examine the various parts or elements of a thing.

Aeroplane. Any form of machine which has planes, and is heavier than air. Usually a flying structure which is propelled by some motive power.

Accumulation. Adding to; bringing together the same or unlike articles.

Ascribable. A reference to some antecedent source. Aeronautics. The science of flying.

Anterior. Meaning the front or forward margin or portion of a body. Artifices. Any artificial product, or workmanship.

Axially. Through the central portion. Thus, the shaft which goes through a cylinder is axially arranged.

Automatic. A thing which operates by its own mechanism; a contrivance which is made in such a manner that it will run without manual operation or care.

Alertness. Quick; being active.

Apex. The point at which two lines meet; also the extreme pointed end of a conical figure.

Ascension. Moving upwardly.

Accessories. The parts of a machine, or artielee which may ha used in connection therewith.

Anemometer. An instrument for measuring the force or the velocity of wind.

Anemograph. An instrument that usually traces a curved line OH paper to make a record of the force or direction, or velocity of the wind.

Anemometrograph. A device which determines the force, velocity and direction of the wind.

Accretion. Adding to little by little. Accelerated. Quiekening; hurrying the process. Abridged. Partly taken away from; shortened. Abrogate. To dispense with; to set aside.

Abnormal Not in the usual manner; not in a regular way.

Alternate. First one and then another; going from one side to the other.

Ancient Lights. An old English law which prevents a neighbor from shutting off sunlight.

Angularly. A line which runs out from another so that the two are not parallel.

Aneroid. Not wet. Applied to the type of barometer where the medium

for determ,ining the pressure is not made of mercury.

Aspirate. A term given by the French to that peculiar action of wing, or other body, which, when placed in certain positions, relative to a current of air, will cause it to be drawn into the current.

Assemblage. The bringing together of the parts or elements of a machine.

Augment. To aid; to add to or increase.

Banked. The term used in aviation which indicates that the machine is turned up so that its supporting surfaces rest against the air, as in alighting.

Barometer. An instrument for determining the air pressure, and thereby indicating altitudes.

Bevel Pinion. A toothed wheel driven by a larger wheel.

Bi-Plane. Two planes. In aviation that type which has two planes, similar in size, usually, and generally placed one above the other so they are separated the same distance from each other, as the width of each of the planes.

Bulge. A hump; an enlargement beyond the normal at any point. Camber, also Cambre. The upward curve in a plane.

Catapult. A piece of mechanism for projecting or throwing a missile.

Carbureter. The device which breaks up the fuel oil, and mixes the proper quantity of air with it before it is drawn into the engine.

Catastrophe. A calamity; a sad ending; loss of life or of property.

Cellular. Made up of small hollows, or compartments; filled with holes.

Celestial. Pertaining to the heavens.

Centrifugal. That force which throws outwardly from a rotating body.

Centripetal. That force, like the attraction of gravity, which draws a body to the center.

Characteristic. Striking; that which is peculiar to some thing or object.

Commensurate. Sufficient; in proper proportion; sufficient for the occasion.

Commercially. Pertaining to the nature of trade; the making of money. Complicated. Not easily explainable; not easy to separate.

Comparatively. Judged by something else; taken with reference to

another object or thing.

Compression. The drawing together; forcing into a smaller compass, or space.

Composition. Made up of different elements, or things. Conceivable. Made up from the imagination.

Concaved. Hollowed: In aviation it has reference to the underside of the plane, which is usually provided, structurally, with a hollow or trough formation.

Conforming. To make alike in form; to bring into harmony. Conjunction. In eonneetion with; joining together.

Convex. A rounded surface; a bulging out.

Conclusion. The end; a finding in law; a reasoning from a certain condition.

Conductivity. The property of materials whereby they will transmit heat along from one part to another, also electricity.

Concentrated. Brought together; assembled in a smaller space. Conclusive. A positive ending; decisive of the matter at issue.

Concentrically. A line which is at all points at the same distance from one point.

Condensation. The act or process of making denser, or being brought together.

Contemplate. To consider; to judge.

Convoys. A protecting force which aeeompanies the transfer of property.

Convection. The diffusion of heat through a liquid or gas. Consistent. A state of harmony; the same at &11 times.

Constant. In mathematics, a figure which never changes; or a figure used as a fixed valuation in a problem.

Controllable. Held within bounds; that which can be within the power to accomplish.

Correctional. The means whereby a fault may be made right. Consequence. The result; that which flows from a preceding action. Counterforce. An action contrary or opposite to the main force.

Counter-balance. Any power equally opposing another.

Counteract. A force acting in opposition to another.

Countercurrent. An air current which sets up in an opposite direction in the path of a moving aeroplane.

Cushioned. An action which takes place against a moving aeroplane, by a sudden gust of air or countercurrent.

Dedicated. To set apart for some special purpose.

Degree. An interval; a grade; a stage; a certain proportion. Deltoid. Shaped like the Greek letter delta.

Density. Closeness of parts.

Demonstration. Making clear; showing up; an exhibition or expression.

Deceptive. The power or tendency to give a false impression. Deterrent. To hold back; to prevent action.

Detracting. The tendency to take away; to belittle. Depressed. To move downwardly.

Destination. The place set for the end of the journey.

Despoiling. To take away from; robbing or taking from another by force or by stealth.

Dependant. Hanging below; projecting from the lower side. Dexterity. Agility; smartness in action.

Deranged. Put out of order; wrongly arranged.

Develop. Brought out; to put into a correct shape or form. Deferred. Put over to another time.

Designedly. With a direct purpose.

Diagonal. Across an object at an angle to one or more aides. Diametrically. Across an object through or near the center thereof. Diagram. A mechanical plan or outline of an object.

Dimension. The distance across an object. The measurement, for instance, of a propeller from tip to tip.

Dynamically. Pertaining to motion as a result of force.

Dispossessed. A term used to indicate the act which removes a person from the possession of property.

Diameter. The measurement across an object. Divest. Taken away from; removed out of.

Disregard. Deliberate lack of attention.

Diversity. The state wherein one is unlike another; dissimilarity.

Drift. The term used to indicate the horizontal motion, or the pull of an aeroplane.

Dragon. A fabulous monster, usually in the form of a serpent. Duplicate. Two; made in exact imitation of an original.

Easement. A legal phrase to designate that right which man possesses, irrespective of any law, to gain access to his property.

Effrontery. Boldness with insolence; rashness without propriety. Effective. To be efficient.

Element. One part of a whole.

Elasticity. Material which will go back to its original form after being distorted, is said to be elastic.

Eliminate. To take away from; to remove a part, or the whole. Elliptical. Oblong with rounded ends.

Elusive. Capable of escaping from; hard to hold.

Elevator. The horizontal planes in front or rear, or in both front and rear of the supporting surfaces of an aeroplane.

Emergency. A sudden occurrence calling for immediate action.

Emplacement. A spot designed to hold heavy field pieces in intrenchments.

Enactment. The formulation of a law; the doing of a special thing. Enunciated. Announced; setting forth of an act or a condition.

Energy. That quality by reason of which anything tends to move or act.

Equidistant. Two points or objects at equal distance from a common point.

Equilibrinm. A balance produced by the action of two or more forces.

Equalizing, One made equal to the other; one side the same as the other.

Equipped. Armed; provided with the proper material, or in the same condition.

Essential. The important part or element.

Essence The real charaeter or element of the thing itself. External. The outermost portion.

Evolution. A gradual change or building up; from a lower to a higher order.

Evolved. Brought out from a crude condition to a better form. Expression. The art of explaining or setting forth.

Expansion. Growing larger; to occupy a greater space. Exerted. To work to the utmost; to put forth in action. Exhilaratiorn. A lively, pleasing or happy sensation.

Exploited. To fully examine and consider, as well as carry out. Extremity. The end; as far as ean be considered.

Facility. Ease of management; to do things without difficulty. Factor. One of the elements in a problem, or in mechanical action. Fascination, Attraetiveness that is pleasing.

Flexure. The capacity to bend and yield, and return to its original position.

Flexible, That which will yield; springy.

Fore and Aft. Lengthwise, as from stem to stern of a ship. Formation. The shape or arrangement of an article or thing.

Formulated. Put into some eonerete form, or so arranged that it may be understood.

Frictionless. Being without a grinding or retarding aotion. Fulcrumed. A resting place for a lever.

Function. The duty or sphere of action in a person, or object.

Glider. An aeroplane, without power, adapted to be operated by an aviator.

Governing. An element which is designed to control a machine in a regular manner.

Graduated. A marked portion, which is regularly laid off to indicate measurements or quantities.

Gravity. The attraction of mass for mass. The tendency of bodies to move toward the earth.

Gravitatior The force with which all bodies attract each other. Gyratory. Having a circular and wheeling as well as a rotary motion.

Gyroscope. A wheel, designed to illustrate the laws of motion, which freely revolves in gimbals within a ring, and when set into motion, objects

to change its plane of rotation.

Hemispherical. The half of a sphere. The half of an apple would be hemispherical.

Hazardous. That which is doubtful; accompanied by danger.

Helicopter. A type of flying machine which has a large propeller, or more than one, revolubly fixed on vertical shafts, by means of which the machine is launched and projected through the air.

Horizontal. Level, like water.

Hydroplane. A term used to designate an aeroplane which is provided with pontoons, whereby it may alight on the water, and be launched from the surface. The term hydroaeroplane is most generally used to indicate this type of machine.

Impact. The striking against; the striking force of one body against another.

Immersed. Placed under water below the surface.

Impinge. To strike against; usually applied where air strikes a plane or a surface at an angle.

Imitation. Similarity; the same in appearance.

Incompatible. Without harmony; incapable of existing together. Incurved. Applied to a surface formation where there is a depression,

or hollow.

Inequalities. Not smooth, or regular; uneven.

Infinitely, Boundless; in great number, or quality; without measure. Initial. The first; that which is at the beginning.

Indestructibility. Not capable of being injured or destroyed. Influenced. Swayed; to be induced to change.

Inherent. That which is in or belongs to itself. Initiating. To teach; to instill; to give an insight.

Indicator. A term applied to mechanism which shows the results of certain operations and enables the user to read the measure, quantity, or quality shown.

Inconceivable. Not capable of understanding; that which cannot be understood by the human mind.

Institute. To start; to bring into operation.

Insignias. Things which are significant of any particular calling or profession.

Instinct. That quality in man or animals which prompts the doing of things independently of any direct knowledge or understanding.

Intermediate. Between; that which may be within or inside the scope of the mind, or of certain areas.

Intervening. The time between; also applied to the action of a person who may take part in an affair between two or more persons.

Interval. A time between.

Investigator. One who undertakes to find out certain things.

Incidence. In physics this is a term to indicate the line which falls upon or strikes another at an angle.

Inverted. Upside down.

Invest. To give to another thing something that it lacked before. Kinetic. Consisting in or depending upon motion.

Laminated. Made up of a plurality of parts. When wooden strips, of different or of the same kinds are glued and then laid together and put under heavy pressure until thoroughly dried, the mass makes a far more rigid structure than if cut out of a single piece.

Launchiug. The term applied to the raising, or starting of a boat, or of a flying object.

Lateral. In mining this is a term to indicate the drifts or tunnels which branch out from the main tunnel. Generally it has reference to a transverse position or direction,--that is, at right angles to a fore and aft direction.

Lift. The vertical motion, or direction in an airship; thus the lift may be the load, or the term used to designate what the ship is capable of raising up.

Ligament. The exceedingly strong tendons or muscles of birds and animals, usually of firm, compact tissues.

Limitations. Within certain bounds; in a prescribed scope. Longitudinally. Usually that direction across the longest part.

Majestically. Grand; exalted dignity; the quality which inspires reverence or fear.

Manipulate. To handle; to conduct so that it will result in a certain way.

Maneuver. A methodical movement or change in troops. Manually. To perform by hand.

Manifestations. The act of making plain to the eye or to the understanding.

Manually-operated. With the hands; a term applied to such machines as have the control planes operated by hand.

Maintained. Kept up; to provide for; to sustain.

Material. The substance, or the matter from which an article is made; also the important thing, or element.

Mass. In physics it is that which in an article is always the same. It differs from weight in the particular that the mass of an article is the same, however far it may be from the center of the earth, whereas weight changes, and becomes less and less as it recedes from the center of the earth.

Margin. The edge; the principal differecee between this word and edge, is, that margin has reference also to a border, or narrow strip along the edge, as, for instance, the blank spaces at the edges of a printed page.

Medievral. Belonging to the Middle Ages.

Mercury. A silver-white liquid metal, usually called quicksilver, and rather heavy. It dissolves most metals, and this process is called amalgamation.

Militate. In determining a question, to have weight, or to influence a decision.

Mobility. Being freely movable; capable of quick change. Modifieation. A change; making a difference.

Monitor. Advising or reproving. Advising or approving by way of caution.

Monstrosities. Anything which is huge, or distorted, or wrong in structure.

Monorail. A railway with a single track, designed to be used by a bicycle form of carriage, with two wheels, fore and aft of each other, and depending for its stability upon gyroscopes, mounted on the carriage.

Momentum. That which makes a moving body difficult to stop. It is the weight of a moving body, multiplied by its speed.

Monoplane. The literal meaning is one plane. As monoplane machines are all provided with a fore and aft body, and each has a wing or plane projecting out from each side of this body, it is obvious that it has two planes instead of one. The term, however, has reference to the fact that it has only one supporting surface on the same plane. Biplanes have two supporting surfaces, one above the other.

Multiplicity. Frequently confounded with plurality. The latter means more than one, whereas multiplicity has reference to a great number, or to a great variety.

Muscular. Being strong; well developed. Negative. The opposite of positive; not decisive.

Neutralize. From the word neuter, which means neither, hence the term may be defined as one which is not a part of either, or does not take up with either side.

Normal Pressure. Normal means the natural or usual, and when applied to air it would have reference to the condition of the atmosphere at that particular place. If the pressure could change from its usual condition, it would be an abnormal pressure.

Notoriously. Generally known, but not favorably so; the subject of general remark; or unfavorably known.

Obscurity. Not well known; in the background; without clear vision; hidden from view.

Obliquely. That which differs from a right angle; neither obtuse nor acute; deviating from a line by any angle except a right angle.

Obvious. That which is readily observed and understood.

Orthopter. That type of flying machine which depends on flapping wings to hold it in space, and to transport it, in imitation of the motion of the wings of birds in flying.

Oscillate. Moving to and fro; the piston of a steam engine has an oscillating motion.

Outline. Describing a marginal line on a drawing; setting forth the principal features of an argument, or the details of a story, or the like.

Overlapping. One placed over the other.

Parabolic. A form of curve somewhat similar to an ellipse.

Pedestal. A standard or support; an upright to hold machinery. Pertinent. Appropriate; pertaining to the subject.

Pectoral. The bone which forms the main rib or support at the forward edge of a bird's wing.

Persistent. Keeping at it; determination to proceed.

Perpendicular. At right angles to a surface. This term is sometimes wrongly applied in referring to an object, particularly to an object which is vertical, meaning up and down. The blade of a square is perpendieular to the handle at all times, but the blade is vertical only when it points to the center of the earth.

Pernicious. Bad; not having good features or possessing wrong attributes.

Pendulum. A bar or body suspended at a point and adapted to swing to and fro.

Perpetual. For all time; unending or unlimited time. Phenomena. Some peculiar happening, or event, or object.

Pitch. In aviation this applies to the angle at which the blades of a propeller are cut. If a propeller is turned, and it moves forwardly in the exact path made by the angle, for one complete turn, the distance traveled by the propeller axially indicates the pitch in feet.

Placement. When an object is located at any particular point, so that it is operative the location is called the placement.

Plane. A flat surface for supporting a flying machine in the air. Plane of movement pertains to the imaginary surface described by a moving body. A bicycle wheel, for instance, when moving forwardly in a straight line, has a plane of movement which is vertical; but when the machine turns in a circle the upper end of the wheel is turned inwardly, and the plane of rhovement is at an angle.

Pliant. Easily yielding; capable of being bent; liable to be put out of shape.

Plurality. See multiplicity. More than one.

Poise. Held in suspension; disposed in a particular way.

Pontoon. Applied to a series of boats ranged side by side to support a walk laid thereon. In aviation it has reference to a float for supporting an

aeroplane.

Ponderous. Large; heavy; difficult to handle. Posterior. The rear end; the opposite of anterior.

Principles. The very nature or essence of a thing; the source or cause from which a thing springs.

Proportion. The relation that exists between different parts or things. Propounded. Questioned; stated; to state formally for consideration Proprietary. A right; the ownership of certain property.

Primitive. The beginning or early times; long ago.

Prelude. A statement or action which precedes the main feature to be presented.

Proximity. Close to; near at hand.

Prototype. That which is used as the sample from, which something is made or judged.

Propeller. The piece of meebanism, with screw shaped blade, designed to be rapidly rotated in order to drive a vessel forwardly. It is claimed by some that the word Impeller would be the more proper term.

Primarily. At the first; the commencement. Precedes. Goes ahead; forward of all.

Propulsive. The force which gives motion to an object. Projected. Thrown forward; caused to fly through the air.

Radially. Out from the center; projecting like the spokes of a wheel. Ratio. The relation of degree, number, amount; one with another.

Reaction. A counterforce; acting against.

Recognize. To know; seeing, hearing, or feeling, and having knowledge therefrom.

Reflection. Considering; judging one thing by the examination of another. A beam of light, or an object, leaving a surface.

Refraction. That peculiarity in a beam of light, which, in passing through water at an angle, bends out of its course and again assumes a direct line after passing through.

Reflex. Turned back on itself, or in the direction from which it came. Requisite. Enough; suffieient for all purposes.

Relegate. To put back or away.

Rectangular. Having one or more right angles.

Reservations. Land which is held by the Government for various purposes.

Resistance. That which holds back; preventing movement. Retarding. Preventing a free movement.

Revoluble. The turning or swinging motion of a body like the earth in its movement around the sun. See Rotative. To cause to move as in an orbit or circle.

Resilient. Springy; having the quality of elasticity. Reversed. Changed about; turned front side to the rear.

Rotative. That which turns, like a shaft. The movement of the earth on its axis is rotative.

Saturation. Putting one substance into another until it will hold no more. For instance, adding salt to water until the water cannot take up any more.

Security. Safety, assuredness that there will be no danger.

Segment. A part eut off from a circle. Distinguished from a sector, which might be likened to the form of one of the sections of an orange.

Sexagonal. Six-sided.

Sine of the Angle. The line dropped from the highest point of an angle to the line which runs out horizontally.

Sinuous. Wavelike; moving up and down like the waves of the ocean. Simulates. To pattern or copy after; the making of the like.

Skipper. A thin flat stone.

Spirally-formed. Made like an auger; twisted.

Stability. In airships that quality which holds the ship on an even and unswerving course, and prevents plunging and side motions.

Structural. Belonging to the features of eonstruetion. Strata. Two or more layers; one over or below the other.

Stream line. In expressing the action of moving air, or an aeroplane transported through air, every part is acted upon by the air. Stream lines are imaginary lines which act upon the planes at all points, and all in the same direction, or angle.

Stupendous. Great; important; above the ordinary.

Substitute. One taken for another; replacing one thing by something else.

Supporting. Giving aid; helping another.

Synchronous. Acting at the same time, and to the same extent. Thus if two wheels, separated from each other at great distances, are so arranged that they turn at exactly the same speed, they are said to turn synchronously.

Tactics. The art of handling troops in the presence of an enemy. It differs from strategy in the particular that the latter word is used to explain the movements or arrangement of forces before they arrive at the battle line.

Tandem. One before the other; one after the other.

Tangent. A line drawn from a circle at an angle, instead of radially. Technically. Pertaining to some particular trade, science or art.

Tenuous. Thin, slender, willowy, slight.

Tetrahedral. This has reference to a form which is made up of a multiplicity of triangularly shaped thin blades, so as to form numerous cells, and thus make a large number of supporting surfaces. Used as a kite.

Theories. Views based upon certain consideration.

Theoretical. Where opinions are founded on certain information, and expressed, not from the standpoint of actual knowledge, but upon conclusions derived from such examinations.

Torsion. A twist; a circular motion around a body. Transmitted. Sent out; conveyed from one point to another.

Transformed. Changed; entirely made over from one thing to another.

Transverse. When a body is shorter from front to rear than from side to side its longest dimension is transversely. Distinguish from lateral, which has reference only to the distance at right angles from the main body.

Translation. The transportation of a body through the air. Trajectory. The path made by a body projected through the air. Triangular. A form or body having three sides and three angles. Typical. In the form of; a likeness to.

Ultimate. The end; the finality; the last that can be said. Uninitiated. Not having full knowledge; withont information.

Unique. Peculiar; something that on account of its peculiar construction or arrangements stands out beyond the others.

Universal. Everywhere; all over the world.

Undulate. To move up and down; a wave-like motion. Utility. Of use; to take advantageous use of.

Unstable. Not having anything permanent; in a ship in flight one that will not ride on an even keel, and is liable to pitch about.

Vacuum. Where air is partly taken away, or rendered rarer.

Valved. A surface which has a multiplicity of openings with valves therein, or, through which air can move in one direction.

Vaunted. To boast concerning; to give a high opinion.

Velocity. Speed; the rate at which an object can move from place to place.

Vertical. A line running directly to the center of the earth; a line at right angles to the surface of water.

Vibratory. Moving from side to side; a regular motion. Volplane. The glide of a machine without the use of power.

Warping. The twist given to certain portions of planes, so as to cause the air to aet against the warped portions.

Weight. The measure of the force which gravity exerts on all objects.