MARVELOUS MECHANISM OF THE MODERN SUBMARINEIts 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.
MARVELOUS MECHANISM OF THE MODERN SUBMARINE
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.
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[905]of J. P. Holland, an American inventor who submitted designs to the United States government in 1895.
SUBMARINE WITH WIRELESS EQUIPMENT
SUBMARINE WITH WIRELESS EQUIPMENT
In 1901 the English Admiralty gave orders to the firm of Vickers, Maxim & Sons, of Barrow, to construct five of theHollandtype 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 improvedGoubet, which was sixteen feet five inches in length, the motive power being electricity. Successful experiments led the French Admiralty to have theGymnoteconstructed 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.
THE PERISCOPE OF THE SUBMARINEis 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.
THE PERISCOPE OF THE SUBMARINE
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, theHollandshave been similarly improved, but other types are also in use. TheLaketype, named after the inventor, Simon Lake, contains an air-lock through which divers may[906]emerge. These vessels have been adopted by Russia.
Germany started withHollands, 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 submarineDeutschlandto 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.
TORPEDO TUBE OF SUBMARINE—DEADLY TORPEDO SHOWN IN TUBE ON RIGHT OF PICTURE
TORPEDO TUBE OF SUBMARINE—DEADLY TORPEDO SHOWN IN TUBE ON RIGHT OF PICTURE
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
How may electricity be called into activity?
Bymechanical power, bychemical action, byheat, and bymagnetic influence.
What is the most ordinary way of exciting electricity?
Byfriction.
Do we know any reason why the means above enumerated should develop electricity from its latent condition?
We areentirely ignorantupon this subject.
When you rub a piece of paper with India-rubber, why does it adhere to the table?
Because thefrictionof the India-rubber against the surface of the paper developselectricity, 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 itselfinvisible, though often accompanied by bothlightandheat.
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 beelectrified, orelectrically 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?
Itdoes; for it will be found that light substances, aftertouchingthe electrified body, willrecede from itjust as actively as they approached it before contact. This is termedelectric 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 ofelectrical attractionandrepulsion.
What is a non-electrified body?
One that holds its own natural quantity of electricityundisturbed.
What happens when an electrified body touches one that is non-electrified?
The electricity contained in the former istransferredin 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 canentirely preventthe passage of electricity, nor any that does not opposesome resistanceto 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?
Themetals,charcoal, theearth,water, andmost fluids, except oils, thehuman 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 islife? Thetheoryof 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 theone fluidtheory. Later physicists arrived at the conclusion that whatever electricity might be, it was not a material substance. As an[908]alternative it was suggested that electricity was a form of energy, but this proved untenable.
HOW ELECTRICITY IS PRODUCED BY THE ACTIVITY OF ELECTRONSDiagram of the Atoms composing the finest point of a piece of AmberELECTRONS flying off from the SILK Atoms, across on to the AMBER Atoms, and so charging the Amber with what is called NEGATIVE ElectricityDiagram of the Atoms composing the thinnest possible thread of SILK; each Atom charged with innumerable NEGATIVE ELECTRONS whirling around within or on the Atoms.Diagram of the Atoms composing the finest point of a piece of AmberELECTRONS flying off from the SILK Atoms, across on to the AMBER Atoms, and so charging the Amber with what is called NEGATIVE ElectricityDiagram of the Atoms composing the thinnest possible thread of SILK; each Atom charged with innumerable NEGATIVE ELECTRONS whirling around within or on the Atoms.
HOW ELECTRICITY IS PRODUCED BY THE ACTIVITY OF ELECTRONS
HOW ELECTRICITY IS PRODUCED BY THE ACTIVITY OF ELECTRONS
Diagram of the Atoms composing the finest point of a piece of AmberELECTRONS flying off from the SILK Atoms, across on to the AMBER Atoms, and so charging the Amber with what is called NEGATIVE ElectricityDiagram of the Atoms composing the thinnest possible thread of SILK; each Atom charged with innumerable NEGATIVE ELECTRONS whirling around within or on the Atoms.
Diagram of the Atoms composing the finest point of a piece of AmberELECTRONS flying off from the SILK Atoms, across on to the AMBER Atoms, and so charging the Amber with what is called NEGATIVE ElectricityDiagram of the Atoms composing the thinnest possible thread of SILK; each Atom charged with innumerable NEGATIVE ELECTRONS whirling around within or on the Atoms.
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.
Diagram of the Atoms composing the finest point of a piece of AmberELECTRONS flying off from the SILK Atoms, across on to the AMBER Atoms, and so charging the Amber with what is called NEGATIVE ElectricityDiagram of the Atoms composing the thinnest possible thread of SILK; each Atom charged with innumerable NEGATIVE ELECTRONS whirling around within or on the Atoms.
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[909]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?
Theydo; each may be made, under certain circumstances, toproduceorexcitethe 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 allmodificationsof 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 ofpositive electricityin thehandandnegativein thefur, 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 thenvery dry, and does notconvey awaythe electricity as fast as it is excited; if the air, on the contrary, weremoist, the electricity would beconducted offnearly 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 oftwo hundred and eighty-eight thousand miles in a secondof 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?
Thelightand thesun’s rays.
Do some animals have the power of exciting electricity within themselves?
Therearecertain animals which aregiftedwith the extraordinary power ofproducing electrical phenomenaby 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 toknock down a man or stun a horse.
Is the electricity generated by these animals the same as that occasioned by the ordinary electrical machine?
Itis the same, and produces thesame effects.
Do vital action and muscular movements in man and animals give rise to electricity?
Theydo; and it can be shown by direct experiment that a person cannot evencontract the muscles of the armwithout exciting an electrical action.
Does change of form or state in bodies generally produce electrical excitation?
Change of form or state is one of themost powerful methodsof 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 isaccumulated electricity, generally dischargedfrom the cloudsto the earth, but sometimes from the earth to the clouds.
What causes the discharge of an electric cloud?
When a cloudoverchargedwith electric fluid approaches another which isundercharged, the fluid rushes from the formerinto the latter, till both contain thesame 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 elevatedfour 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?
Thedisturbancecaused in theairwhen successive discharges of accumulated electricity take place.
Into how many kinds has lightning been divided?
Three.
What are they?
Thezig-zag lightning,sheet lightning, andball lightning.
Why is lightning sometimes forked?
Because the lightning cloud is at agreat distance; and theresistance of the airis 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 theleast 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 elseseveral flashes intermingled.
FRANKLIN AND HIS KITE
FRANKLIN AND HIS KITE
What other form does lightning occasionally assume?
Sometimes the flash isglobular, which is the most dangerous form of lightning.
Does a discharge produce a flash when it passes through good conductors?
Itdoes not, but passes quietly and invisibly.
What is heat lightning?
Sometimes it is thereflectionin the atmosphere of the lightnings of stormsvery 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 producesgreat evaporation, and the conversion ofwater into vaporalways developselectricity.
How long is the duration of a flash of lightning?
Arago has demonstrated that it does not exceed themillionth part of a second.
With what velocity is lightning, or the electric fluid which gives rise to its appearance, supposed to move?
Not less thantwo hundred and fifty thousand miles per second.
By whom was the identity of lightning and electricity first established?
ByDr. 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 anon-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 wasliable to pass fromit, 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 thenecessary ruleshave beenobserved, 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 donot, as many suppose,attract the lightning toward the buildingon which they are situated; they simplydirect its course, andfacilitatethepassageof thefluidin 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 certainnoiseproceeding 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 asudden displacement of the airproduced 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 theeffect 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 isnear the earth; and as all the vibrations of the air (on which sound depends) reach the ear atthe same moment, they seem like one vast sound.
Why is the thunder generally heard several moments after the flash?
Because it has along distanceto travel. Lightning travels nearly amilliontimes faster than thunder; if, therefore, the thunder hasa great distance to come, it will not reach the earth till a considerable timeafter 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 wholesecond of timeto 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 appearancesseen in theskyat 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?
Electricityin 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 thenorth, but in the southern hemisphere it appears in thesouth: it seems to originate at or near thepoles 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 notlocal, 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 fromone 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 thewinterthan in the summer, and are only seen atnight.
Do they also occur in the day-time?
The aurora is known toaffect the magnetic needleand 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 affordslight sufficientfor many of theordinary outdoor employments.
Is there any connection between magnetism and electricity?
There is every reason to believe that magnetism and electricity are butmodifications of one force.
What is a loadstone or a natural magnet?
It is anore 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 arenot; they are found in many places in theUnited States. InArkansas, 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 termedpoles.
What is the origin of the terms “magnet” and “magnetism”?
The loadstone or natural magnet was first found atMagnesia, in Lydia, Asia, whence were derived the names.
Can a natural magnet communicate its attractive properties to other bodies by contact?
Itcan, and that too without anyapparent lossof attractive strength.
What bodies are capable of being magnetized by contact with natural magnets?
Ironandsteelare 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 thesteelitdoes, but the soft ironloses its poweras 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 broughtneara magnet becomes by induction itself a magnet.
What do you mean by induction?
It is the production oflike effectsincontiguous 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 constantlyturn the same parttowards the north pole and the opposite part towards the south pole of the earth.
What are the poles of a magnet?
They are theendsof 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?
Theextremities 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 abar of steelwhich is amagnet, suspended in such a way that it canfreely turnto the north or south.
DIAGRAM SHOWING THE VARIATION OF THE MAGNETIC AND GEOGRAPHICAL POLES
DIAGRAM SHOWING THE VARIATION OF THE MAGNETIC AND GEOGRAPHICAL POLES
What is a mariner’s compass?
It is adelicate steel bar or needlebalanced 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 doesnot; 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 theChinese: it was known in Europe, and used in the Mediterranean, in the thirteenth century.
How were the compasses of that time constructed?
They were merelypieces of loadstonefixed to acork, which floated on the surface of water.
Is the earth itself supposed to be a magnet?
It is undoubtedly agreatmagnet.
Is iron under certain circumstances rendered magnetic by the inductive action of the earth’s magnetism?
Mostiron barsandrails, as the vertical bars of windows, that have stood for a considerable time in a perpendicular position, will be found to bemagnetic.
If we suspend a bar of soft iron sufficiently long in the air, will it assume magnetic properties?
Itwillgradually become magnetic; and although when it is first suspended it points indifferently in any direction, it will at last pointnorth 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 withone end on the ground, slightly inclined towards the north, and then struck onesmart blowwith ahammerupon the upper end, it will immediately acquirepolarity, and exhibit the attractive and repellant properties of a magnet.
What is a horseshoe magnet?
It is amagnetic barbent into theform 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 termedhorseshoe magnets. Several of these are frequently joined together with their similar poles in contact; they then constitute amagnetic 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 aperfect 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 aperfect magnet.
What is galvanism?
It is the production ofelectrical disturbanceby 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, adistinct thrillwill pass through the tongue, a metallic taste will diffuse itself, and, if the eyes are closed, a sensation oflightwill be evident at the same moment.
To what is this result owing?
To achemical actiondeveloped the moment the two metals touched each other.
Thesalivaof the tongueoxidizesa portion of thezinc, which exciteselectricity, 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?
ByGalvani, professor of anatomy at Bologna, Italy, in 1790.
Having occasion to dissect several frogs, he hung up their hind legs on somecopper 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 aseries 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?
Agalvanicorvoltaic battery.
Why are the terms “galvanic” and “voltaic” applied?
They originated in honor ofGalvaniandVolta, the Italian philosophers who first developed these phenomena of chemical electricity, and the means of producing them.