Chapter I: The Anglo-Saxon Period, 449-1066 (18)

THE TWO TYPES.--A _monoplane_ is a machine with a single spread of surface supporting it. The best known example of a monoplane is the Bleriot. _Biplanes_ have two supporting surfaces, the one above the other; the Wright and Farman machines are machines of this type. There are other machines which have been invented which have more supporting surfaces than this, the most successful of them all being the Roe triplane. But at present, at any rate, the advantage lies between the monoplane and the biplane, the other machines not yet having reached a sufficiently high standard to be able to compete with them.

The monoplane and the biplane have both their own special uses. The monoplane is obviously the lighter machine, and its head resistance is much less, hence it follows logically that its speed will be greater than that of a biplane. But the biplane is a much more stable machine than the monoplane; it will therefore probably be safer and will certainly be able to carry a greater weight.

In the making of aëroplanes wood is usually used for the framework. Specially selected wood is taken, usually from the spruce, hickory, ash, or birch, since wood combines in itself the strength and tenacity of metal without its weight. The fabric with which this frame is covered is more difficult to obtain, since it must contain in itself all the qualities of strength, lightness, smoothness, etc., without any tendencies to shrink, or rot, or burn.

The biplane carries a load of from two and one-half to three and one-half pounds per square foot of surface; the monoplane from three and one-half to six pounds per square foot. The load per horse power in each case is from thirty to forty pounds. In speed the biplane ranges from thirty-five to forty-five miles per hour, as against forty to sixty miles per hour attained by the monoplane.

PRACTICAL USES.--From the very first days the value of the aëroplanes, from a military point of view, has been realized, not as a weapon of offense so much as of intelligence. It would, in fact, be difficult to imagine a better means of scouting and reconnoitering than is afforded by the flying-machine. Its gradually increasing radius of action renders it available for strategical no less than for tactical reconnaissance; its easy mode of progress and absence of vibration allow the most accurate observations to be made and sketch-maps to be drawn. For dispatch-carrying over difficult country its usefulness is also considerable. Its employment for purposes of offense is much more hazardous. On the other hand, it is practically immune from artillery or rifle fire from the land, especially when flying at a fair altitude.

As a commercial vehicle, and for transport, the aëroplane, owing to its relatively low carrying power, is restricted in its usefulness. With increasing reliability, however, it may well assume a portion of the functions of the motor car.

THE MODERN AIRSHIP

The development of the balloon began in 1783, and was the work of two brothers, Joseph and Etienne Montgolfier, who were the sons of a paper manufacturer of Annonay, France.

The latest and most successful experimenter is Count Zeppelin, a German inventor, whose name has been given to the huge dirigible airships known as Zeppelins. Between these there has been a long list of inventors and experimenters who met with varying degrees of success; but the Zeppelins stand paramount.

From the year 1897 the development of the airship was the special work of the Count Zeppelin. In 1900 he made his first flight with a dirigible balloon which carried five men. It was made of aluminum, supported by gas bags and driven by two motors, each about sixteen horse power. His first experiment met with some success, but the first Zeppelin airship was succeeded by another in 1905 with greater motor power; this was wrecked and was succeeded by a third, which met with great success. This airship carried eleven passengers and attained a speed of about thirty-six miles an hour. The fourth Zeppelin airship succeeded in traveling about two hundred and fifty miles in eleven hours, but was wrecked by a storm in 1908, the wreckage catching fire and completely destroying the ship.

_Zeppelin VII._ had a total length of no less than four hundred and eighty-five feet, a diameter of forty-six feet, and a volume of 690,000 cubic feet. The vessel was fitted with three engines totaling some four hundred and twenty horse power and capable of driving the vessel at thirty-five miles an hour. On one occasion she carried thirty-two people and made a journey of three hundred miles in nine hours.

In the meantime many other experiments had been carried out, notably by Santos Dumont, who circled the Eiffel Tower in the face of a fresh wind.

_Dirigibles_ are divided into three types--(_a_) _rigid_, in which there is a framework or skeleton, over which a skin is stretched and within which a number of balloons are placed; (_b_) _semi-rigid_, in which the lower part only of the balloon is distended on a flat framework; and (_c_) _non-rigid_, when a gas-bag of elongated form has a long girder suspended below it. The propellers are most usually mounted in pairs on each side of the car, but Zeppelin attached them to the balloon itself. To prevent pitching, an “empennage” of flat surfaces is usually arranged near the after-end.

SOME FACTS ABOUT ZEPPELINS.--In shape an ordinary Zeppelin airship is a long cylinder with semisphere-like ends and a keel running the whole length of the bottom thereof. In appearance from a distance the cylinder and pointed ends appear circular in shape, _i.e._ in cross-section, but in reality this is not so, both being sixteen sided. About one-third the distance from either end of the keel are small boat-like structures suspended from the hull, so close to it that at these places there is a gap in the hull to make room for them. They are rigidly connected with the metallic hull of the airship and help to support it either when the vessel rests on the ground or is towed or driven along the water.

Within these structures are the crew and engines, while above, but outward on each side of the rigid hull and connected with it by means of outriggers, are two pairs of aërial propellers. These are placed at an equal distance out on either side and in the same horizontal plane, so that their united propulsive action shall act centrally along the line of head resistance. The crew can walk through the keel (originally V-shaped) from end to end, or from one boat to the other, the passage being illuminated by means of suitable windows. An observer can also climb through the hull to take observation from the top. Telephones, electric bells, and speaking-tubes are all employed to transmit orders.

CONSTRUCTION OF THE FRAME.--The frame of the rigid hull is built of sixteen longitudinals or girders of trellised or latticed metal; it runs the whole length of the airship and is riveted at regular intervals to cross-sections of latticed girders. Each of these cross-sections is in the form of a sixteen-sided figure or wheel, with latticed rims strengthened by radial rods running from a center flange or boss to the outer rims. The main hull is thus divided into a number of compartments, each separated from one another by means of these latticed radial discs or wheel-like structures and otherwise enclosed by the sixteen latticed girder longitudinals or beams. Each of these compartments contains a gas-bag or balloonette filled with hydrogen; the balloonette fairly fills the compartment, and each bag exerts its proportionate lift. A netting of ramie cords is stretched from wheel to wheel diagonally, between the beams at their inner corners, while the outward corners of the beams are joined by strong wires arranged diagonally for the purpose of imparting rigidity.

The whole frame is covered externally with a strong fabric, which forms the outer skin or wall of the hull. Air-spaces naturally exist between this covering, the inflated balloonettes, and the wheel-like divisions. The entire airship owes its buoyancy to the balloonettes filled with hydrogen, while the outer framework and covering act as a protection against the sun, foul weather, and external shocks.

WAR ZEPPELINS.--Monstrous as the above ships are, they are quite dwarfed by the recent type of military Zeppelins. The latter carry motors aggregating no less than nine hundred horse power. The length varies from five hundred to eight hundred feet, and the diameter is proportional. The gas capacity exceeds a million cubic feet.

AËROPLANE VERSUS AIRSHIP.---On the airship’s side the following strong points are claimed: (1) Greater manœuvering power than the aëroplane, more especially with respect to rapidity of ascent; (2) greater offensive power, _i.e._ ability to carry heavier guns owing to its far greater lifting capacity; (3) ability to stand still or hover in the air over one spot (for bomb-dropping), or remain stationary in the air, end on to the enemy, for the purpose of obtaining a steady gun platform; (4) greater flying durability, _i.e._ ability to remain longer in the air at a stretch; (5) ability to fly at night.

MANNING THE AIRSHIP.--The crew of a military airship includes the following: the pilot, the engineer, the steersman, the wireless operator, and last but by no means least the observer. The total number of the crew varies with the size of the airship, and the particular mission in view. The pilot is the captain of the airship, and is responsible for (1) the route, (2) the altitude or elevation at which the airship travels, and (3) the maintenance of the correct pressure on the envelope. The steersman maintains the course ordered him, by means of a compass or by special instructions which may be given him, and also controls the altitude or elevation as ordered. The engineer naturally looks after the engines and the mechanical part of the apparatus with which the airship is fitted.

Its interior is a steel maze of intricate machinery that fills it from end to end, and makes it easily the most remarkable of modern marine craft.]

THE SUBMARINE

Though the submarine boat has only recently been brought to a high degree of practical efficiency, its history extends back to the seventeenth century, and even beyond. The modern submarine, however, whether of the American, English, or German type, has followed the model of J. P. Holland, an American inventor who submitted designs to the United States government in 1895.

In 1901 the English Admiralty gave orders to the firm of Vickers, Maxim & Sons, of Barrow, to construct five of the _Holland_ type and subsequently several were constructed for the United States government.

To France belongs the credit of making submarine boats a real factor in naval warfare. In 1881 M. Goubet designed a small submarine boat, and in 1885 an improved _Goubet_, which was sixteen feet five inches in length, the motive power being electricity. Successful experiments led the French Admiralty to have the _Gymnote_ constructed at Toulon in 1888; she was fifty-six feet five inches long, with a displacement of thirty tons, her motive power being electricity stored in accumulators, which gave her a radius of thirty-two miles at eight knots. Her trials decided the French authorities to have more vessels built, and by 1901 there were some eleven completed.

is its ever watchful eye. Ordinarily the top of the periscope extends about eighteen inches above the waves. Continually revolved at a high rate of speed by an electric motor, the mirrors bring into focus the whole panorama of the upper seas so that the commander can follow in the smallest detail what is passing above him, locate vessels to be attacked, and submerge at will in the presence of danger.]

In America, the _Hollands_ have been similarly improved, but other types are also in use. The _Lake_ type, named after the inventor, Simon Lake, contains an air-lock through which divers may emerge. These vessels have been adopted by Russia.

Germany started with _Hollands_, which they have developed along their own lines. The submarine boat is found in all navies now, and has proved an enormously efficient craft; displacements of one thousand tons are not unusual and speeds as well as radius of action have shown great improvement. The Diesel engine has been largely responsible for this. In manœuvers the craft have come up to expectation completely, the experience in actual war has shown them to be among the most formidable of war craft.

There are two distinct types of submarine vessel--the submarine proper, and the submersible. The submarine sinks through the exhaustion of all its buoyancy, and she sinks at once; the submersibles are forced under.

The latter, though equipped to travel on the surface of the water, are specially equipped for sinking quickly out of sight as the occasion arises. The most improved types, such as the recent German U-boats, have lofty armor plated conning towers, torpedo tubes, mounted guns, periscopes, and wireless equipments.

While in the present European war the submarines have shown themselves to be formidable weapons in skillful hands, they are not so formidable as to ring the death-knell of the large battleship, still less perhaps of the swift battle cruiser. Victory has usually rested with the more powerful ship and the heavier guns.

The present-day submarine suffers from two serious drawbacks: (1) inability to see under the water; (2) inefficient speed--the latter being much slower compared with the speed of fast surface boats. The chief chance of a submarine attacking an enemy with success is to come upon him unawares.

The periscopes and other optical tubes with which submarines are fitted, suffer also from many disabilities; and the fact that many collisions have occurred while using them, shows that they are not yet perfect. Obviously one showing not only what is forward of the submarine but what is on the surface of the water on every side is best. One of the drawbacks from which they suffer is the encrustation of salt on their reflecting surfaces; and small though the exposed surface of the periscope may be, there is always the chance of a vigilant enemy detecting it.

THE SUBMARINE IN PEACE.--It is pleasant to record that this invention, like many others of its kind, has not been devoted solely to war, but that peace also can claim its services. The recent remarkable trans-Atlantic voyages of the German submarine _Deutschland_ to American ports is an illustration of their importance to commercial transportation under critical conditions. Since, too, the submarine can sink or dive down to moderate depths, it is obvious it can be used for purposes of underwater salvage, construction, and exploration.

As an aid in the construction of breakwaters, the blowing-up of submerged wrecks in comparatively speaking shallow waters, in searching for sunken treasures, and as an aid to marine explorations in suitable waters, the peace or working submarine is likely to be of untold value.

ELECTRICITY AND MAGNETISM

WHAT IS ELECTRICITY? -- MEANS OF EXCITING ELECTRICITY -- ELECTRIFIED
AND NON-ELECTRIFIED BODIES -- CONDUCTORS AND NON-CONDUCTORS OF
ELECTRICITY -- ELECTRICAL MACHINES -- POSITIVE AND NEGATIVE
ELECTRICITY -- VELOCITY OF ELECTRICITY -- PRINCIPAL AGENTS IN NATURE
EXCITING ELECTRICITY -- LIGHTNING -- THREE FORMS OF LIGHTNING --
SHEET AND HEAT LIGHTNING -- DURATION OF A FLASH OF LIGHTNING --
PLACES DANGEROUS IN A THUNDER STORM -- HOW A TREE INFLUENCES
LIGHTNING -- LIGHTNING CONDUCTORS -- THEIR PROPER PRINCIPLE OF
CONSTRUCTION -- FRANKLIN’S EXPERIMENT WITH A KITE -- IDENTITY OF
LIGHTNING AND ELECTRICITY -- UTILITY OF LIGHTNING-RODS -- WHAT IS
THUNDER? -- WHAT OCCASIONS THE ROLLING OF THUNDER? --
AURORA-BOREALIS -- EXTENT OF THE AURORA -- HEIGHT OF THE AURORA --
APPEARANCE -- AURORA-BOREALIS OCCURS IN THE DAY-TIME -- WHAT IS
GALVANISM? -- HOW GALVANIC ELECTRICITY WAS DISCOVERED --
CONSTRUCTION OF A GALVANIC BATTERY -- ORIGIN OF THE TERM “GALVANISM”
-- POLES OF A BATTERY -- MEANS BY WHICH GALVANIC-ELECTRICITY IN
QUANTITY CAN BE DEVELOPED -- DIFFERENT FORMS OF GALVANIC BATTERIES
-- LIGHT AND HEAT PRODUCED BY GALVANISM -- PRINCIPLES AND PROCESSES
OF ELECTRO-METALLURGY -- MAGNETISM -- NATURAL MAGNETS -- WHERE FOUND
-- BODIES CAPABLE OF BEING MAGNETIZED -- INDUCTION -- MAGNETIC
NEEDLE -- THE MAGNETIC COMPASS -- DISCOVERY AND FIRST USE OF THE
COMPASS -- ELECTRO-MAGNETISM -- WHEN AND HOW DISCOVERED -- HOW IRON
BARS BECOME MAGNETIC -- HORSE-SHOE MAGNETS -- EXCITATION OF
MAGNETISM -- MORSE’S MAGNETIC TELEGRAPH -- TELEGRAPH, MAGNETIC,
PRINCIPLES OF -- INTELLIGENCE, HOW CONVEYED BY -- ELECTRIC DYNAMO
AND MOTORS -- WIRELESS TELEGRAPHY -- WIRELESS TELEPHONE -- X-RAYS

ELECTRICITY

_How may electricity be called into activity?_

By _mechanical power_, by _chemical action_, by _heat_, and by _magnetic influence_.

_What is the most ordinary way of exciting electricity?_

By _friction_.

_Do we know any reason why the means above enumerated should develop
electricity from its latent condition?_

We are _entirely ignorant_ upon this subject.

_When you rub a piece of paper with India-rubber, why does it adhere
to the table?_

Because the _friction_ of the India-rubber against the surface of the paper develops _electricity_, to which this adhesiveness is mainly to be attributed.

_Does electricity present any appearance by which it can be known?_

No; electricity, like heat, is in itself _invisible_, though often accompanied by both _light_ and _heat_.

_When a substance, by friction or by any other means, acquires the
property of attracting other bodies, in what state is it said to
be?_

It is said to be _electrified_, or _electrically excited_; and its motion towards other bodies, or of other bodies towards it, is ascribed to a force called electric attraction.

_Does an electrified body exercise any other influence than an
attractive one?_

It _does_; for it will be found that light substances, after _touching_ the electrified body, will _recede from it_ just as actively as they approached it before contact. This is termed _electric repulsion_.

Thus, if we take a dry glass rod, rub it well with silk, and present it to a light pith ball, or feather, suspended from a support by a silk thread, the ball or feather will be attracted towards the glass. After it has adhered to it a moment, it will fly off, or be repelled. The same will happen if sealing-wax be rubbed with dry flannel, and a like experiment made; but with this remarkable difference, that when the glass repels the ball, the sealing-wax attracts it, and when the wax repels, the glass will attract. These phenomena are examples of _electrical attraction_ and _repulsion_.

_What is a non-electrified body?_

One that holds its own natural quantity of electricity _undisturbed_.

_What happens when an electrified body touches one that is
non-electrified?_

The electricity contained in the former is _transferred_ in part to the latter.

Thus, on touching the end of a suspended silk-thread with a piece of excited wax, the silk will be excited, as will be shown by its moving towards a book, piece of metal, or any other object placed near it.

_Do all bodies conduct or allow electricity to pass through them
equally well?_

Although there is no substance that can _entirely prevent_ the passage of electricity, nor any that does not oppose _some resistance_ to its passage, yet it moves with a much greater facility through a certain class of substances than through others. Those substances which facilitate its passage are called conductors; those that retard or almost prevent it, are called non-conductors.

_What substances are good conductors of electricity?_

The _metals_, _charcoal_, the _earth_, _water_, and _most fluids_, except oils, the _human body_, etc., are good conductors.

_What substances obstruct the passage of electricity, or are
“non-conductors”?_

_Glass_, _resin_, _oil_, _silk_, _sulphur_, _dry air_, etc., etc., are non-conductors.

_What is an electrical machine?_

An electrical machine is an arrangement by which quantities of electricity can be collected and discharged.

One type of the electrical machine most usually employed consists of a large circular plate of glass, mounted upon a metallic axis, and supported upon pillars fixed to a secure base, so that the plate can, by means of a handle, be turned with ease. Upon the supports of the glass, and fixed so as to press easily but uniformly on the plate, are four rubbers; and flaps of silk, oiled on one side, are attached to these, and secured to fixed supports by several silk cords. When the machine is put in motion, these flaps of silk are drawn tightly against the glass, and thus the friction is increased, and electricity excited.

_Do we know what electricity is?_

No; a complete and final answer to this question is no more possible than the answer to the question--what is _life_? The _theory_ of electricity, however, opens up possibilities of the most fascinating nature; it gives us a wonderfully clear conception of which might be called the inner mechanism of electricity; and it even introduces us to the very atoms of electricity.

_Give a short outline of the theory of electricity._

EARLY THEORIES.--Early writers on the nature of electricity supposed it to be either a fluid of peculiar properties or else two fluids whose properties were complementary to each other or of opposite kinds; Franklin held the _one fluid_ theory. Later physicists arrived at the conclusion that whatever electricity might be, it was not a material substance. As an alternative it was suggested that electricity was a form of energy, but this proved untenable.

_Diagram of the Atoms composing the finest point of a piece of Amber_

_ELECTRONS flying off from the SILK Atoms, across on to the AMBER Atoms, and so charging the Amber with what is called NEGATIVE Electricity_

_Diagram of the Atoms composing the thinnest possible thread of SILK; each Atom charged with innumerable NEGATIVE ELECTRONS whirling around within or on the Atoms._]

ELECTRON THEORY.--This, with certain reservations, is held by the scientific world of today. All matter is believed to be constituted of minute particles called “atoms,” whose diameter has been estimated at about one millionth of a millimeter. Up to a few years ago the atom was believed to be quite indivisible, but it has been proved beyond doubt that this is not the case. An atom may be said to consist of two parts, one much larger than the other. The smaller part is negatively electrified, and is the same in all atoms; while the larger part is positively electrified, and varies according to the nature of the atom. The small negatively electrified portion of the atom consists of particles called “electrons,” and these electrons are believed to be indivisible units or atoms of negative electricity.

The electrons in an atom are not fixed, but move with great velocity, in definite orbits. They repel one another, and are constantly endeavoring to fly away from the atom, but they are held in by the attraction of the positive core. So long as nothing occurs to upset the constitution of the atom, a state of equilibrium is maintained and the atom is electrically neutral; but immediately the atom is broken up by the action of an external force of some kind, one or more electrons break their bonds and fly away to join some other atom. An atom which has lost some of its electrons is no longer neutral, but is electro-positive; and similarly, an atom which has gained additional electrons is electro-negative.

THE ELECTRIC CURRENT.--A current of electricity is believed to be nothing more or less than a stream of electrons, set in motion by the application of an electro-motive force. Some substances are good conductors of electricity, while others are bad conductors or non-conductors. In order to produce an electric current, that is a current of electrons, it is evidently necessary that the electrons should be free to move. In good conductors, which are mostly metals, it is believed that the electrons are able to move from atom to atom without much hindrance, while in a non-conductor their movements are hampered to such an extent that interatomic exchange of electrons is almost impossible.

_Does electricity seem to exist in two different states or
conditions?_

It does; and to designate these two conditions, the terms positive and negative have been employed. Thus a body which has an overplus of electricity is called positive, and one that has less than its natural quantity is called negative.

_Do light, heat, and electricity appear to have some properties in
common?_

They _do_; each may be made, under certain circumstances, to _produce_ or _excite_ the other. All are so light, subtle, and diffusive, that it has been found impossible to recognize in them the ordinary characteristics of matter. Some suppose that light, heat, and electricity are all _modifications_ of some common principle.

_Why does the fur of a cat sparkle and crackle when rubbed with the
hand in cold weather?_

Because the friction between the hand and fur produces an excitation of _positive electricity_ in the _hand_ and _negative_ in the _fur_, and an interchange of the two causes a spark, with a slight noise.

_Why does this experiment work best in very cold weather?_

Because the air is then _very dry_, and does not _convey away_ the electricity as fast as it is excited; if the air, on the contrary, were _moist_, the electricity would be _conducted off_ nearly as fast as it was excited by friction, and its effects would not therefore be so manifest.

_With what velocity is electricity transmitted through good
conductors?_

With a velocity so great that the most rapid motion produced by art appears to be actual rest when compared to it. Some authorities have estimated that electricity will pass through copper wire at the rate of _two hundred and eighty-eight thousand miles in a second_ of time--a velocity greater than that of light.

_What agents are undoubtedly the most active in producing and
exciting electricity in the operations of nature?_

The _light_ and the _sun’s rays_.

_Do some animals have the power of exciting electricity within
themselves?_

There _are_ certain animals which are _gifted_ with the extraordinary power of _producing electrical phenomena_ by an effort of muscular or nervous energy. Among these the electrical eel and the torpedo are most remarkable.

_How powerful a charge of electricity can the electrical eel send
forth when in full vigor?_

Sufficient to _knock down a man or stun a horse_.

_Is the electricity generated by these animals the same as that
occasioned by the ordinary electrical machine?_

It _is the same_, and produces the _same effects_.

_Do vital action and muscular movements in man and animals give rise
to electricity?_

They _do_; and it can be shown by direct experiment that a person cannot even _contract the muscles of the arm_ without exciting an electrical action.

_Does change of form or state in bodies generally produce electrical
excitation?_

Change of form or state is one of the _most powerful methods_ of exciting electricity.

Water, in passing into steam by artificial heat, or in evaporating by the action of the sun or wind, generates large quantities of electricity. The crystallization of solids from liquids, all changes of temperature, the growth and decay of vegetables, are also instrumental in producing electrical phenomena.

_What is lightning?_

Lightning is _accumulated electricity_, generally discharged _from the clouds_ to the earth, but sometimes from the earth to the clouds.

_What causes the discharge of an electric cloud?_

When a cloud _overcharged_ with electric fluid approaches another which is _undercharged_, the fluid rushes from the former _into the latter_, till both contain the _same quantity_.

_Is there any other cause of lightning besides the one just
mentioned?_

Yes; sometimes mountains, trees, and steeples will discharge the lightning from a cloud floating near, and sometimes the electricity passes from the earth into the clouds.

_How high are the lightning clouds from the earth?_

Sometimes they are elevated _four or five miles high_, and sometimes actually touch the earth with one of their edges; but they are rarely discharged in a thunder storm when they are more than seven hundred yards above the surface of the earth.

_What is a thunder storm?_

The _disturbance_ caused in the _air_ when successive discharges of accumulated electricity take place.

_Into how many kinds has lightning been divided?_

_Three._

_What are they?_

The _zig-zag lightning_, _sheet lightning_, and _ball lightning_.

_Why is lightning sometimes forked?_

Because the lightning cloud is at a _great distance_; and the _resistance of the air_ is so great that the electrical current is diverted into a zig-zag course.

_How does the resistance of the air make the lightning zig-zag?_

As the lightning condenses the air in the immediate advance of its path, it flies from side to side, in order to pass where there is the _least resistance_.

_Why is the flash sometimes quite straight?_

Because the lightning cloud is near the earth, and as the flash meets with very little resistance, it is not diverted; in other words, the flash is straight.

_What is sheet lightning?_

Either the reflection of distant flashes not distinctly visible or beneath the horizon, or else _several flashes intermingled_.

_What other form does lightning occasionally assume?_

Sometimes the flash is _globular_, which is the most dangerous form of lightning.

_Does a discharge produce a flash when it passes through good
conductors?_

It _does not_, but passes quietly and invisibly.

_What is heat lightning?_

Sometimes it is the _reflection_ in the atmosphere of the lightnings of storms _very remote_, the storms themselves being so far distant that their thunders cannot be heard. This phenomenon is also occasioned by the play of silent flashes of electricity between the earth and the clouds, the amount of electricity developed not being sufficient to produce any other effects than the mere flash of light.

_Why is lightning more common in summer and in autumn than in spring
and winter?_

Because the heat of summer and autumn produces _great evaporation_, and the conversion of _water into vapor_ always develops _electricity_.

_How long is the duration of a flash of lightning?_

Arago has demonstrated that it does not exceed the _millionth part of a second_.

_With what velocity is lightning, or the electric fluid which gives
rise to its appearance, supposed to move?_

Not less than _two hundred and fifty thousand miles per second_.

_By whom was the identity of lightning and electricity first
established?_

By _Dr. Franklin_, at Philadelphia, in 1752.

The manner in which this fact was demonstrated, was as follows:

Having made a kite of a large silk handkerchief stretched upon a frame, and placed upon it a pointed iron wire connected with the string, he raised it upon the approach of a thunder storm. A key was attached to the lower end of the hempen string holding the kite, and to this one end of a silk ribbon was tied, the other end being fastened to a post. The kite was now insulated, and the experimenter for a considerable time awaited the result with great solicitude. Finally, indications of electricity began to appear on the string; and on Franklin presenting his knuckles to the key, he raised an electric spark. The rain beginning to descend, wet the string, increased its conducting power, and vivid sparks in great abundance flashed from the key.

_Why was the kite insulated when Franklin fastened the key to the
post with a silk ribbon?_

Because the silk was a _non-conductor_, and would not allow the electricity received upon the kite to pass off by means of the string to the ground.

_Was this experiment one of great danger and risk?_

It was; because the whole amount of electricity contained in the thunder cloud was _liable to pass from_ it, by means of the string, to the earth, notwithstanding the use of the silk insulator.

_Have we any proof of the utility of lightning rods?_

The experience of a hundred years has shown that when all the _necessary rules_ have been _observed_, the protection is perfect, as far as human effort can avail.

_Is a building more or less liable to be struck when furnished with
a good lightning conductor?_

Lightning conductors do _not_, as many suppose, _attract the lightning toward the building_ on which they are situated; they simply _direct its course_, and _facilitate_ the _passage_ of the _fluid_ in the most direct way to the earth, only when a discharge must inevitably occur. There is no attraction, but the lightning takes the road which offers the least resistance.

_What is thunder?_

It is a certain _noise_ proceeding apparently from the clouds, which usually follows, after a greater or less interval, the appearance of a flash of lightning.

_How is it supposed to be occasioned?_

The usual explanation offered is a _sudden displacement of the air_ produced by the electrical discharges in which the lightning is evolved.

Others have supposed that the passage of the electric current creates a vacuum, and that the air rushing in to fill it produces the sound. Any explanation that has yet been offered is not altogether satisfactory.

_What occasions the rolling of the thunder?_

It has been ascribed to the _effect of echo_; but the true cause probably is, that the sound is developed by the lightning in passing through the air, and consequently separate sounds are produced at every point through which the lightning passes.

_Why is thunder sometimes one vast crash?_

Because the lightning cloud is _near the earth_; and as all the vibrations of the air (on which sound depends) reach the ear at _the same moment_, they seem like one vast sound.

_Why is the thunder generally heard several moments after the
flash?_

Because it has a _long distance_ to travel. Lightning travels nearly a _million_ times faster than thunder; if, therefore, the thunder has _a great distance to come_, it will not reach the earth till a considerable time _after the flash_.

_Can we not tell the distance of a thunder cloud by observing the
interval which elapses between the flash and the peal?_

Yes; the flash is instantaneous, but the thunder will take a whole _second of time_ to travel three hundred and eighty yards; hence, if the flash be five seconds before thunder, the cloud is nineteen hundred yards off.

_i.e._ 380 × 5 = 1900 yards.

_What is the aurora borealis or northern lights?_

_Luminous appearances_ seen in the _sky_ at night-time. Sometimes streaks of blue, purple, green, red, etc., and sometimes flashes of light, are seen.

_What is the cause of the aurora borealis or northern lights?_

_Electricity_ in the higher regions of the atmosphere is undoubtedly an active agent in producing this phenomenon.

_Is the aurora ever seen in other parts of the heavens than towards
the north?_

In the northern hemisphere it always appears in the _north_, but in the southern hemisphere it appears in the _south_: it seems to originate at or near the _poles of the earth_, and is consequently seen in its greatest perfection within the arctic and antarctic circles.

_What is known concerning the extent of the aurora?_

It is not _local_, but it is seen simultaneously at places widely remote from each other, as in Europe and America.

_What calculations have been made respecting the height of the
aurora?_

The height of the appearances varies from _one to two hundred miles_; they sometimes appear within the region of the clouds, and very near to the earth.

_Do the auroras appear at any particular seasons and times?_

They appear more frequently in the _winter_ than in the summer, and are only seen at _night_.

_Do they also occur in the day-time?_

The aurora is known to _affect the magnetic needle_ and the telegraph; and as the effects upon these instruments are noticed by day as well as by night, there can be no doubt of the occurrence of the aurora at all hours. The intense light of the sun renders the auroral light invisible during the day.

_Of what utility are the auroral appearances in the polar regions?_

During the long polar night, when the sun is absent, the aurora appears with a magnificence unknown in other regions, and affords _light sufficient_ for many of the _ordinary outdoor employments_.

MAGNETISM

_Is there any connection between magnetism and electricity?_

There is every reason to believe that magnetism and electricity are but _modifications of one force_.

_What is a loadstone or a natural magnet?_

It is an _ore of iron_, known as the “_protoxide of iron_,” or “_magnetic oxide of iron_,” which is capable of attracting other pieces of iron to itself; and if suspended freely by a thread, and left to take its own position, it will arrange itself so that its extremities will point towards the north and south poles of the earth.

_Are natural magnets rare?_

They are _not_; they are found in many places in the _United States_. In _Arkansas_, especially, an ore of iron possessing remarkably strong attractive powers is very abundant.

The magnetic ore is usually of a dark gray hue, and possesses but little metallic luster. If a piece of this ore be dipped in iron filings, or a number of small needles, they will generally be found collected and clinging together in great quantities at two opposite extremities, whilst the middle portion is nearly destitute. The magnetic property, whatever it may be, seems therefore to be collected and act with the greatest energy at two opposite extremes; these have been termed _poles_.

_What is the origin of the terms “magnet” and “magnetism”?_

The loadstone or natural magnet was first found at _Magnesia_, in Lydia, Asia, whence were derived the names.

_Can a natural magnet communicate its attractive properties to other
bodies by contact?_

It _can_, and that too without any _apparent loss_ of attractive strength.

_What bodies are capable of being magnetized by contact with natural
magnets?_

_Iron_ and _steel_ are the substances most susceptible of this influence, but brass, nickel, and cobalt can also become magnets.

_Does the magnetism imparted to a piece of soft iron, or steel, by
contact with a natural magnet, remain permanent in their
substances?_

In the _steel_ it _does_, but the soft iron _loses its power_ as soon as it is removed from the magnet.

_Is it necessary that absolute contact should take place between a
magnet and a piece of soft iron to render the latter a magnet?_

No, every piece of soft iron brought _near_ a magnet becomes by induction itself a magnet.

_What do you mean by induction?_

It is the production of _like effects_ in _contiguous bodies_. In electricity or magnetism, it is the influence exerted by an electrified or magnetized body through a non-conducting medium without any apparent communication of a current.

_What is meant by the directive power of the magnet?_

It is that power which will cause a magnet, when suspended freely, to constantly _turn the same part_ towards the north pole and the opposite part towards the south pole of the earth.

_What are the poles of a magnet?_

They are the _ends_ of the magnet, and are denominated north and south, according as they point to the north or south poles of the earth.

_What are the poles of the earth?_

The _extremities of the earth’s axis_, or the points on the surface of the globe through which the axis passes.

_What is a magnetic needle?_

Simply a _bar of steel_ which is a _magnet_, suspended in such a way that it can _freely turn_ to the north or south.

_What is a mariner’s compass?_

It is a _delicate steel bar or needle_ balanced upon a pivot placed beneath its center of gravity in such a way that it can turn horizontally without obstruction. This needle is usually inclosed in a box, upon the bottom of which is a card, with the various points--north, south, east, west, etc., etc., marked upon it.

Such a needle, if the box containing it be placed on a level surface, will generally be observed to vibrate more or less, till it settles in such a direction that one of its extremities or poles will point towards the north, and the other consequently towards the south. If the position of the box be altered or reversed, the needle will always turn and vibrate again, till its poles have attained the same direction as before.

_Does the compass needle always point exactly north and south?_

It does _not_; its natural direction is towards the north and south poles, but it seldom points due north or south.

_Who first discovered the fact that a magnet would invariably point
to the north and the south, and made use of this knowledge in
constructing a compass?_

It is claimed to have been discovered by the _Chinese_: it was known in Europe, and used in the Mediterranean, in the thirteenth century.

_How were the compasses of that time constructed?_

They were merely _pieces of loadstone_ fixed to a _cork_, which floated on the surface of water.

_Is the earth itself supposed to be a magnet?_

It is undoubtedly a _great_ magnet.

_Is iron under certain circumstances rendered magnetic by the
inductive action of the earth’s magnetism?_

Most _iron bars_ and _rails_, as the vertical bars of windows, that have stood for a considerable time in a perpendicular position, will be found to be _magnetic_.

_If we suspend a bar of soft iron sufficiently long in the air, will
it assume magnetic properties?_

It _will_ gradually become magnetic; and although when it is first suspended it points indifferently in any direction, it will at last point _north and south_.

_How may a bar of iron, such as a kitchen poker, be made immediately
magnetic, without resorting to the use of other magnets?_

If the bar devoid of magnetism is placed with _one end on the ground_, slightly inclined towards the north, and then struck one _smart blow_ with a _hammer_ upon the upper end, it will immediately acquire _polarity_, and exhibit the attractive and repellant properties of a magnet.

_What is a horseshoe magnet?_

It is a _magnetic bar_ bent into the _form of a horseshoe_.

When a piece of iron not magnetic is brought in contact with a common magnet, it will be attracted by either pole; but the most powerful attraction takes place when both poles can be applied to the surface of the piece of iron at once. The magnetic bars are for this purpose bent into the shape of the letter U, and are termed _horseshoe magnets_. Several of these are frequently joined together with their similar poles in contact; they then constitute a _magnetic battery_, and are very powerful, either for lifting weights, or charging other magnets.

_If we break a magnet across the middle, what happens?_

Each fragment becomes converted into a _perfect magnet_; the part which originally had a north pole acquires a south pole at the fractured end, and the part which originally had a south pole, gets a north pole.

_If we divide a magnet to the extreme degree of mechanical fineness
possible, will the pieces possess magnetic powers?_

Each fragment, however small, will be a _perfect magnet_.

GALVANISM

_What is galvanism?_

It is the production of _electrical disturbance_ by chemical action.

_What is the most simple manner of illustrating the production of
this electricity?_

If we place a piece of silver on the tongue, and a piece of zinc underneath it, no effect will be produced as long as the two metals are kept asunder; but when their ends are brought together, a _distinct thrill_ will pass through the tongue, a metallic taste will diffuse itself, and, if the eyes are closed, a sensation of _light_ will be evident at the same moment.

_To what is this result owing?_

To a _chemical action_ developed the moment the two metals touched each other.

The _saliva_ of the tongue _oxidizes_ a portion of the _zinc_, which excites _electricity_, for no chemical action ever takes place without producing electricity. Upon bringing the ends of the two metals together, a slight current passes from one to the other.

_By whom was the production of galvanic electricity first noticed?_

By _Galvani_, professor of anatomy at Bologna, Italy, in 1790.

Having occasion to dissect several frogs, he hung up their hind legs on some _copper hooks_, until he might find it necessary to use them for illustration. In this manner he happened to suspend a number of the copper hooks on an iron balcony, when, to his great astonishment, the limbs were thrown into violent convulsions.

_On investigating the phenomena what did Galvani discover?_

He found that whenever the nerves of a frog’s leg were touched by one metal and the muscles by another, convulsions took place on bringing the two different metals in contact.

_What is the simplest way of exciting a current of galvanic
electricity?_

By arranging a _series of metal plates in a pile_, placing them in pairs, with a wet cloth between them, it being necessary that one of each pair should be more easily oxidized than the other. The simple contact of these plates will produce a feeble and continued galvanic current.

_What is such an arrangement of plates for producing electrical
currents called?_

A _galvanic_ or _voltaic battery_.

_Why are the terms “galvanic” and “voltaic” applied?_

They originated in honor of _Galvani_ and _Volta_, the Italian philosophers who first developed these phenomena of chemical electricity, and the means of producing them.

_Are there many metals or other substances which, when brought
together, are capable of producing galvanic action?_

The number is _quite large_; among them we may enumerate the following: _zinc_, _lead_, _tin_, _antimony_, _iron_, _brass_, _copper_, _silver_, _gold_, _platinum_, _black lead_ or _graphite_, and _charcoal_.

_Will any two of these brought together produce a galvanic current?_

They _will_; but they possess the power in _different degrees_; and the more remote they stand from each other in the order above given, the more decidedly will the chemical electricity be developed.

Thus zinc and lead will produce a voltaic battery, but it will be much less active than zinc and iron, or the same metal and copper, and this last less active than zinc and platinum, or zinc and charcoal.

_Does galvanic or voltaic electricity appear to consist of two
kinds, positive and negative, as in ordinary electricity?_

It does; positive electricity always flows _from the metal which is acted upon_ most powerfully, and negative electricity _from the other_.

_What do we mean when we speak of a galvanic circuit?_

The connection of the two metals in the battery, so that the positive and negative electricities can _meet, and flow in opposite directions_.

_At what point in the circuit will the manifestations of electricity
be most apparent?_

At the point where the _two currents meet_.

_What is meant by the poles of the battery?_

The two metals forming the elements of the battery are generally connected by copper wires; the _ends_ of these wires, or the _terminal points_ of any other connecting medium used, are called the poles of the battery.

Thus, when zinc and copper poles are used, the end of the wire conveying positive electricity from the zinc would be the positive pole, and the end of the wire conveying negative electricity from the copper plate would be the negative pole. Faraday describes the poles of the battery as the doors by which electricity enters into or passes out of the substance suffering decomposition.

A very simple, and at the same time an active, galvanic circuit may be formed by an arrangement as represented in the accompanying illustration. The current of positive electricity, when the circuit is closed, passes from the zinc, through the liquid, to the copper, and from the copper, along the conductors to the zinc. A current of negative electricity traverses the circuit also, from the copper to the zinc, in a direction precisely reversed.

_By what chemical action can the greatest abundance of galvanic
electricity be developed?_

By the _oxidation of metallic zinc_ by weak sulphuric acid.

(1) _Grove’s Cell._--Z. Zinc plate in dilute sulphuric acid; P. platinum plate in strong nitric acid. (2) _Daniell’s Cell._--Z. Zinc rod in porous pot P containing dilute sulphuric acid; C. copper plate in outer vessel containing copper sulphate solution. (3) _Leclanche Cell._--Zinc in sal-ammoniac solution; carbon slab in charcoal and manganese dioxide.]

_The electricity developed by the action of a single pair of plates
immersed in acid water is very feeble: how can it be increased?_

By increasing the _number of the plates_ and the quantity of the liquid, we increase the intensity of the electricity developed.

ACTION WITHIN A VOLTAIC CELL.--Let us try to see now how an electric current is set up in a simple voltaic cell, consisting of a zinc plate and a copper plate immersed in dilute acid. First we must understand the meaning of the word _ion_.

If we place a small quantity of salt in a vessel containing water, the salt dissolves, and the water becomes salt, not only at the bottom where the salt was placed, but throughout the whole vessel. This means that the particles of salt must be able to move through the water. Salt is a chemical compound of sodium and chlorine, and its molecules consist of atoms of both these substances. It is supposed that each salt molecule breaks up into two parts, one part being a sodium atom, and the other a chlorine atom, and further, that the sodium atom loses an electron, while the chlorine atom gains one. These atoms have the power of traveling about through the solution, and they are called ions, which means “wanderers.”

An ordinary atom is unable to wander about in this way, but it gains traveling power as soon as it is converted into an ion, by losing electrons if it be an atom of a metal, and by gaining electrons if it be an atom of a non-metal.

Returning to the voltaic cell, we may imagine that the atoms of the zinc which are immersed in the acid are trying to turn themselves into ions, so that they can travel through the solution. In order to do this each atom parts with two electrons, and these electrons try to attach themselves to the next atom. This atom, however, already has two electrons, and so in order to accept the newcomers it must pass on its own two. In this way electrons are passed on from atom to atom of the zinc, then along the connecting wire, and so to the copper plate. The atoms of zinc which have lost their electrons thus become ions, with power of movement. They leave the zinc plate immediately, and so the plate wastes away or dissolves. So we get a constant stream of electrons traveling along the wire connecting the two plates, and this constitutes an electric current.

_What are the most ordinary effects produced by the developed
electricity of a large galvanic battery?_

The _production of sparks_ and _brilliant flashes of light_, the heating and fusing of metals, the deflagration of gunpowder and other inflammable substances, and the decomposition of water, saline compounds, and metallic oxides.

_How may the most splendid artificial light known be produced?_

By fixing pieces of pointed charcoal or carbon to the wires connected with opposite poles of a powerful galvanic battery, and bringing them into contact.

_What does this produce?_

Electric light.

_Can intense heat be developed by the action of the galvanic battery
as well as intense light?_

The _greatest artificial heat_ man has yet succeeded in producing has been through the agency of the _galvanic battery_.

_What refractory substances can be fused by the aid of the galvanic
battery?_

All the metals, including platinum, can be _readily melted_; quartz, sulphur, magnesia, slate and lime are liquefied; and the diamond fuses, boils, and becomes converted into coal.

The above simple voltaic battery, or cell, consists of a plate of copper and one of zinc dipping into a vessel containing dilute sulphuric acid to twenty of water by volume. When these plates are joined externally by a wire or other conductor a current flows from the copper plates, called the positive pole of the battery, to the zinc plate, called the negative pole of the battery. This is due to the fact that a difference of _potential_ is set up between the plates on immersion in the acid, in consequence of which an electro-motive force is generated that drives the current round the circuit. The potential between the plates is maintained by the chemical action now going on in the cell. This action results in the gradual consumption of the zinc plate with formation of zinc sulphate and evolution of hydrogen at the copper plate. In a short time the current in the circuit falls off in consequence of _local action_ and _polarization_.]

_What is electrotyping, or electro-metallurgy?_

It is the art or process of _depositing_, from a _metallic solution_, through the agency of galvanic electricity, a _coating_ or _film_ of metal upon some other substance.

_Upon what principles is it accomplished?_

The process is based on the fact, that when a galvanic current is passed through a solution of some metal, as a solution of sulphate of copper (sulphuric acid and copper), _decomposition takes place_; the metal is separated in a metallic state, and attaches itself to the negative pole, or to any substance that may be attached to the negative pole; while the acid or other substance before in combination with the metal, goes to, and is deposited on the positive pole.

In this way a medal, a wood-engraving, or a plaster cast, if attached to the negative pole, may be covered with a coating of copper; if the solution had been one containing silver or gold, the substance would have been covered with a coating of silver or gold instead of copper.

_How can the thickness of the deposits be regulated?_