Part 232

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.

_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.

_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?_

The thickness of the deposit, providing the supply of the metallic solution be kept constant, will depend on the _length of time the object is exposed to the influence of the battery_.

ELECTRO-MAGNETISM

_What is electro-magnetism?_

It is the magnetism developed through the agency of _electrical_ or _galvanic action_.

_What were the earliest phenomena observed which indicated a relation between magnetism and electricity?_

It was noticed that _ships’ compasses_ have their directive power impaired by lightning, and that sewing needles could be rendered magnetic by electric discharges passed through them.

_What discovery, made by Prof. Oersted of Copenhagen, established beyond a doubt the connection of electricity and magnetism?_

He ascertained that a magnetic needle placed near a metallic wire connecting the poles of a galvanic battery was compelled to change its direction, and that the new direction it assumed was determined by its position in _relation to the wire_ and to the direction of the current _transmitted along the wire_.

Thus, if a needle be inclosed in a wire not touching it at any point, and a current of electricity pass through the wire, the needle will be made to move in accordance with the direction of the current.

_What other important discovery was made about the same time?_

It was found that if a piece of soft iron, not possessing magnetic power sufficient to elevate a grain weight, be placed within a coil of copper wire through which a galvanic current is passing, it will become, through the influence of the current, a _powerful magnet_; and will, so long as the current flows, sustain weights amounting to many hundreds of pounds.

_Is the magnetic power of the bar found to be wholly dependent on the existence of the current?_

It _is_; the moment the current stops, the weights _fall away_ from the bar in obedience to the law of gravity.

_How great weights have been lifted by magnets formed in this manner?_

An electro-magnet constructed by Prof. Henry was capable of elevating and sustaining about a _ton weight_.

_Upon what principle does the construction of the Morse magnetic telegraph depend?_

Upon the principle that a current of _electricity_ circulating about a bar of soft iron is capable of _rendering it a magnet_.

_Why is it necessary, in conveying the telegraph wires, to support them upon glass or earthen cylinders?_

These are used for the purpose of insuring the perfect _insulation_ of the wires, since but for this the electricity would pass down a damp pole to the earth, and be lost.

_Is there any truth in the idea that many persons have, that some principle passes along the telegraphic wires when intelligence is transmitted?_

This supposition is _wholly erroneous_; the word current, as something flowing, conveys a false idea, but we have no other term to express electrical progression.

_How can we gain an idea of what really takes place, and of the nature of the influence transmitted?_

The earth and all matter are _reservoirs of electricity_; if we disturb this electricity at Boston by voltaic influence, its pulsations may be felt in Chicago. Suppose the telegraphic wire were a tube, extending from Boston to Chicago, filled with water. Now, if one drop more is forced into it at Boston, a drop must fall out at Chicago, but no drop was caused to pass from Boston to Chicago. Something similar to this occurs in the transmission of electricity.

_What was the earliest important industrial application of electricity?_