If a piece of zinc and copper joined by a wire be dipped in a liquid--generally weak sulphuric acid--which will act chemically on the metals, a current is produced. Such an arrangement is called a couple, or cell. If many cells are connected, then it is called a battery.

What is Thermo-electricity?

If two bars of any unlike metal--for example, antimony and bis.m.u.th--be soldered together at one end, and the other ends be connected by a wire and then the soldered end heated, a current will flow.

What effects are produced by currents?

They produce heat, light, decomposition and combination in liquid chemical compounds; they melt all metals, excite magnetism, and in the animal body excite movements of the muscles.

Can you specify these effects?

A strong battery produces heat in such a degree that all metals can be melted. Light is produced in flashes, or if the end of the leading wires are connected with two pencils of hard carbon, and brought very near together, then a brilliant light, or arc, called the voltaic arc, is produced. This is the dazzling bright light which we call electric light. The chemical effect of a current in decomposing compound substances is called electrolysis. In this way water can be decomposed into its compounds, hydrogen and oxygen; copper sulphate into sulphur and metallic copper, etc. In this way we can deposit strong adherent films of metal on the surface of any conductor; for if the article to be coated be attached to the negative electrode of a battery, and dipped into a solution of the metal with which we desire to coat the article, say copper or silver, and the positive electrode be attached to a plate of copper and also dipped into a liquid, when the current pa.s.ses, the metal will be decomposed and deposited in a uniform layer over the article at the negative electrode. This process is called _electro-plating_.

What is Electrotyping?

It is the process of copying medals, type, wood-cuts, engraved copper and steel plates, etc., by means of electrical deposition. It is chiefly used for making, from the ordinary movable types, plates of fixed metallic types, for printing books.

Describe the process.

The article to be copied is first covered with black-lead, and then a mould is made of it in wax or gutta-percha. This mould is placed in a solution of sulphate of copper, and attached to the negative pole of the battery, while a plate of copper is hung from the positive pole.

The electric current decomposes the copper, which is deposited in a thin film upon the mould. This film is removed and stiffened by being backed with metal.

What is the difference between Electrotyping and Stereotyping?

In stereotyping, a plaster of Paris mould is taken from the types, and upon this mould melted type-metal is poured, which, when hardened, makes a solid plate.

Is there any other method of stereotyping?

Yes; that known as the paper process. A uniform sheet of soft matter is formed by pasting together sheets of thin, tough tissue paper. The types are oiled, and the soft, moist sheet is placed on them and beaten down with a stiff brush until it receives an impression of the type-form. Both are then run through a press, and on being taken out the paper is found to form a perfect mould. Into this mould the type-metal is poured and the plate formed.

Can you tell me some magnetic effects of the current?

All conductors become magnetic during the pa.s.sage of a current through them, and thereby acquire all the properties of a magnet. There are bodies which are natural magnets, and they are called permanent magnets. Those which become magnets only during the pa.s.sage of a current are called electro-magnets.

Do you know any application of those magnets?

They are employed in a great variety of electrical apparatus, princ.i.p.ally in telegraphy.

When was the first telegraph established?

It was made in 1836, being invented by Prof. Steinheil, of Munich, and adopted by the government of Bavaria. It was 12 miles long, and the signals were made by small bells.

Who was the inventor of the telegraph in this country?

Samuel F.B. Morse, who was born at Charlestown, Ma.s.s., April 27, 1791.

He began life as a painter, but did not give his whole attention to art--chemistry and experiments in electricity and galvanism claiming much of his time. He first conceived the idea of the telegraph in 1832, and exhibited his invention to Congress in 1837. He struggled on with scanty means, and was about to give up in despair when Congress appropriated $30,000 for an experimental line, which was opened on May 12, 1844, between Washington and Baltimore. Prof. Morse died in 1872, but not before he had reaped honors and fortune from his invention.

How rapidly does the electric current travel through the wires?

From experiments made it appears to be about 15,400 miles in a second.

Can more than one message be sent at the same time on the same wire?

Yes; it is possible now to send several messages at the same time.

What is a Cable?

It is a telegraph wire under water. Prof. Morse, in 1842, laid a wire insulated by a covering of hemp coated with pitch-tar and India-rubber between Governor"s Island and the Battery, New York. Several attempts were made in other countries.

What was the greatest telegraphic undertaking?

That of connecting Europe with America by a submarine cable spanning the ocean, which was commenced in 1857 and completed August 5, 1858.

To whom do we owe this grand undertaking?

This honor is entirely due to Mr. Cyrus W. Field. Mr. Field was born at Stockbridge, Ma.s.s., on November 30th, 1819. In 1853 he became interested in ocean telegraphy, and after many reverses succeeded in laying the first cable in August, 1858. The message sent by Queen Victoria to the President of the United States, consisting of 99 words, occupied 67 minutes in transmitting. In September of the same year this cable ceased to work, but the energy of Field restored confidence, and another cable was made and laid down in July, 1865, but after 1200 miles were deposited it was lost. In 1866 another was made and successfully laid in July. In August the lost cable was found and spliced, and carried to the western sh.o.r.e.

What is a Dynamo-electric machine?

A machine by which very powerful currents can be obtained directly from mechanical power. In these, by means of a steam-engine or other power, a number of coils of wire called the armature are set into rapid revolution between the poles of powerful electro-magnets. All currents are caused to flow from the armature in one direction by means of a contrivance called the commutator. Very successful machines of this sort are the Gramme machine, the Siemens, and, princ.i.p.ally, the so-called Brush machine. By these the electric light is now generally produced.

What is a Lightning Rod?

It is a rod of iron placed against a building to protect it from lightning. Three or four feet of one end is in the moist ground or in water, while several feet of the other end extend above the highest part of the building. The upper end of the rod is pointed with copper or some other metal which will not easily corrode.

By whom was it invented?

By Benjamin Franklin, and first announced by him in his "Poor Richard"s Almanac" for 1753. Franklin was born at Boston, Ma.s.s., in 1706. By his talents, prudence, and honesty he rose from humble beginnings to be one of the foremost men of his time. He was one of the committee of five chosen by Congress to prepare the "Declaration of Independence" which he with other patriots afterwards signed.

Towards the close of the year 1776 he was sent as amba.s.sador to the French Court, and remained in Europe some time. He returned home in 1785, and died at Philadelphia on the 17th of April, 1790.