The development of the battery began with Galvani in 1790, and Volta in 1800. Galvani discovered that a frog's legs would exhibit violent muscular contraction when its exposed nerves were touched with one metal and its muscles were touched with another metal, the two metals being connected. The effect was due to an electric current generated and acting with contractile effect on the muscles of the frog's legs.

[Ill.u.s.tration: FIG. 1.]

From this phenomenon, the chemical action of acids upon metals and the production of an electric current were observed, and the voltaic pile was invented. This consisted of alternate discs of copper and zinc, separated by layers of cloth steeped in an acidulated solution. This was the invention of Volta. From this grew the Daniell battery, invented in 1836 by Prof. Daniell of London, quickly followed by those of Grove, Smee, and others. These batteries were more constant or uniform in the production of electricity, were free from odors, and did not require frequent cleaning, as did the plates of the voltaic pile, which were important results for telegraphic purposes. The Daniell battery in its original form employed an acidulated solution of sulphate of copper in a copper cell containing a porous cup, and a cylinder of amalgamated zinc in the porous cup and surrounded by a weak acid solution. In the ill.u.s.tration, which shows a slightly modified form, a cruciform rod of zinc within a porous cup is surrounded by a copper cell, the whole being enclosed within a gla.s.s jar.

[Ill.u.s.tration: FIG. 2.--DANIELL'S BATTERY.]

The second element of the telegraph--the conducting wire--was scarcely an invention in itself, and the fact that electricity would act at a distance through a metal conductor had been observed many years before the Morse telegraph was invented. In 1823, however, Weber discovered that a copper wire which he had carried over the houses and church steeples of Gottingen from the observatory to the cabinet of Natural Philosophy, required no special insulation. This was an important observation in the practical construction of telegraph lines. One of even greater importance, however, was that of Prof. Steinheil, of Munich, who, in 1837, made the discovery of the practicability of using the earth as one-half, or the return section, of the electric conductor.

[Ill.u.s.tration: FIG. 3.--PROF. HENRY'S INTENSITY MAGNET.]

The third element of the telegraph is the electro-magnet. This, and its arrangement as a relay in a local circuit, was a most important invention, and contributed quite as much to the success of the telegraph as did the inventions of Prof. Morse. It may be well to say that an electro-magnet is a magnet which attracts an iron armature when an electric current is sent through its coil of wire, and loses its attractive force when the circuit is cut off, thereby rendering it possible to produce mechanical effects at a distance through the agency of electrical impulses only. For the electro-magnet the world is chiefly indebted to Prof. Joseph Henry, formerly of Princeton, N. J., but later of the Smithsonian Inst.i.tution. In 1828 he invented the energetic modern form of electro-magnet with silk covered wire wound in a series of crossed layers to form a helix of multiple layers around a central soft iron core, and in 1831 succeeded in making practical the production of mechanical effects at a distance, by the tapping of a bell by a rod deflected by one of his electro-magnets. This experiment may be considered the pioneer step of the telegraph.

[Ill.u.s.tration: FIG. 4.

HENRY.

STURGEON.

Great as was the work of Prof. Henry, he must share the honors with a number of prior inventors who made the electro-magnet possible.

Electro-magnetism, the underlying principle of the electro-magnet, was first discovered in 1819 by Prof. Oersted, of Copenhagen. In 1820 Schweigger added the multiplier. Arago in the same year discovered that a steel rod was magnetized when placed across a wire carrying an electric current, and that iron filings adhered to a wire carrying a voltaic current and dropped off when the current was broken. M. Ampere subst.i.tuted a helix for the straight wire, and Sturgeon, of England, in 1825 made the real prototype of the electro-magnet by winding a piece of bare copper wire in a single coil around a varnished and insulated iron core of a horse shoe form, but the powerful and effective electro-magnet of Prof. Henry is to-day an essential part of the telegraph, is in universal use, and is the foundation of the entire electrical art. It is unfortunate that Prof. Henry did not perpetuate the records of his inventions in patents, to which he was opposed, for there is good reason to believe that he was also the original inventor of the important arrangement of the electro-magnet as a relay in local circuit, and other features, which have been claimed by other parties upon more enduring evidence, but perhaps with less right of priority.

[Ill.u.s.tration: FIG. 5.--MORSE'S FIRST MODEL PENDULUM INSTRUMENT.]

The fourth and great final addition to the telegraph which crowned it with success was the Morse register and alphabetical code, the invention of Prof. Samuel F. B. Morse, of Ma.s.sachusetts. Prof. Morse's invention was made in 1832, while on board ship returning from Europe. He set up an experimental line in 1835, and got his French patent October 30, 1838, and his first United States patent June 20, 1840, No. 1647. In 1844 the United States Congress appropriated $30,000 to build a line from Baltimore to Washington, and on May 24, 1844, the notable message, "What Hath G.o.d wrought?" went over the wires.

[Ill.u.s.tration: FIG. 6.--THE MORSE CODE.]

Morse's first model, his pendulum instrument of 1837, is ill.u.s.trated in Fig. 5. A pendulum carrying a pencil was in constant contact with a strip of paper drawn beneath the pencil. As long as inactive the pencil made a straight line. The pendulum carried also an armature, and an electro-magnet was placed near the armature. A current pa.s.sed through the magnet would draw the pendulum to one side. On being released the pendulum would return, and in this way zigzag markings, as shown at 4 and 5, would be produced on the strip of paper, which formed the alphabet. A different alphabet, known as the Morse Code, was subsequently adopted by Morse, and in 1844 the receiving register shown at Fig. 7 was adopted, which finally a.s.sumed the form shown at Fig. 8.

The alphabet consisted simply of an arrangement of dots and dashes in varying sequence. The register is an apparatus operated by the combined effects of a clock mechanism and electro-magnet. Under a roll, see Fig.

8, a ribbon of paper is drawn by the clockwork. A lever having an armature on one end arranged over the poles of an electro-magnet, carries on the other end a point or stylus. When an electric impulse is sent over the line the electro-magnet attracts the armature, and the stylus on the other end of the lever is brought into contact with the paper strip, and makes an indented impression. A short impulse gives a dot, and a long impulse holds the stylus against the paper long enough to allow the clock mechanism to pull the paper under the stylus and make a dash. By the manipulation of a key for closing the electric circuit the short or long impulse may be sent, at the pleasure of the operator.

[Ill.u.s.tration: FIG. 7.--MORSE RECEIVER.]

This const.i.tuted the completed invention of the telegraph, and on comparing the work of Profs. Henry and Morse, it is only fair to say that Prof. Henry's contribution to the telegraph is still in active use, while the Morse register has been practically abandoned, as no expert telegrapher requires the visible evidence of the code, but all rely now entirely upon the sound click of the electro-magnet placed in the local circuit and known as a sounder, the varying time lengths of gaps between the clicks serving every purpose of rapid and intelligent communication.

The invention of the telegraph has been claimed for Steinheil, of Munich, and also for Cooke and Wheatstone, in England, but few will deny that it is to Prof. Morse's indefatigable energy and inventive skill, with the preliminary work of Prof. Henry, that the world to-day owes its great gift of the electric telegraph, and with this gift the world's great nervous forces have been brought into an intimate and sensitive sympathy.

[Ill.u.s.tration: FIG. 8.--PERFECTED MORSE REGISTER.]

Whenever an invention receives the advertis.e.m.e.nt of public approval and commercial exploitation, the development of that invention along various lines follows rapidly, and so when practical telegraphic communication was solved by Henry, Morse, and others, further advances in various directions were made. Efforts to increase the rapidity in sending messages soon grew into practical success, and in 1848 _Bain's Chemical Telegraph_ was brought out. (U. S. Pats. No. 5,957, Dec. 5, 1848, and No. 6,328, April 17, 1849.) This employed perforated strips of paper to effect automatic transmission by contact made through the perforations in place of the key, while a chemically prepared paper at the opposite end of the line was discolored by the electric impulses to form the record. This was the pioneer of the automatic system which by later improvements is able to send over a thousand words a minute.

[Ill.u.s.tration: FIG. 9.--HOUSE PRINTING TELEGRAPH.]

[Ill.u.s.tration: FIG. 10.--STOCK BROKER'S "TICKER," WITH GLa.s.s COVER REMOVED.]

In line with other efforts to increase the capacity of the wires, the _duplex telegraph_ was invented by Dr. William Gintl, of Austria, in 1853, and was afterwards improved by Carl Frischen, of Hanover, and by Joseph B. Stearns, of Boston, Ma.s.s, who in 1872 perfected the duplex (U.

S. Pats. No. 126,847, May 14, 1872, and No. 132,933, Nov. 12, 1872).

This system doubles the capacity of the telegraphic wire, and its principle of action permits messages sent from the home station to the distant station to have no effect on the home station, but full effect on the distant station, so that the operators at the opposite ends of the line may both telegraph over the same wire, at the same time, in opposite directions. This system has been further enlarged by the quadruplex system of Edison, which was brought out in 1874 (and subsequently developed in U. S. Pat. No. 209,241, Oct. 22, 1878). This enabled four messages to be sent over the same wire at the same time, and is said to have increased the value of the Western Union wires $15,000,000.

In 1846 Royal C. House invented the _printing telegraph_, which printed the message automatically on a strip of paper, something after the manner of the typewriter (U. S. Pat. No. 4,464, April 18, 1846). The ingenious mechanism involved in this was somewhat complicated, but its results in printing the message plainly were very satisfactory. This was the prototype of the familiar "_ticker_" of the stock broker's office, seen in Figs. 10 and 11. In 1856 the Hughes printing telegraph was brought out (U. S. Pat. No. 14,917, May 20, 1856), and in 1858 G. M.

Phelps combined the valuable features of the Hughes and House systems (U. S. Pat. No. 26,003, Nov. 1, 1859).

[Ill.u.s.tration: FIG. 11.--RECEIVING MESSAGE ON STOCK BROKER'S "TICKER."]

_Fac Simile_ telegraphs const.i.tute another, although less important branch of the art. These accomplished the striking result of reproducing the message at the end of the line in the exact handwriting of the sender, and not only writing, but exact reproductions of all outlines, such as maps, pictures, and so forth, may be sent. The fac simile telegraph originated with F. C. Bakewell, of England, in 1848 (Br. Pat.

No. 12,352, of 1848).

The Dial Telegraph is still another modification of the telegraph. In this the letters are arranged in a circular series, and a light needle or pointer, concentrically pivoted, is carried back and forth over the letters, and is made to successively point to the desired letters.

Among other useful applications of the telegraph is the _fire alarm system_. In 1852 Channing and Farmer, of Boston, Ma.s.s., devised a system of telegraphic fire alarms, which was adopted in the city of Boston (U. S. Pat. No. 17,355, May 19, 1857), and which in varying modifications has spread through all the cities of the world, introducing that most important element of time economy in the extinguishment of fires. Hundreds of cities and millions of dollars have been thus saved from destruction.

Similar applications of local alarms in great numbers have been extended into various departments of life, such as _District Messenger Service_, _Burglar Alarms_, _Railroad-Signal Systems_, _Hotel-Annunciators_, and so on.

[Ill.u.s.tration: FIG. 12.--TELEGRAPHING BY INDUCTION.]

For furnishing current for telegraphic purposes the dynamo, and especially the storage battery, have in late years found useful application. In fact, in the leading telegraph offices the storage battery has practically superseded the old voltaic cells.

_Telegraphing by induction_, _i. e._, without the mechanical connection of a conducting wire, is another of the developments of telegraphy in recent years, and finds application to telegraphing to moving railway trains. When an electric current flows over a telegraph line, objects along its length are charged at the beginning and end of the current impulse with a secondary charge, which flows to the earth if connection is afforded. It is the discharge of this secondary current from the metal car roof to the ground which, on the moving train, is made the means of telegraphing without any mechanical connection with the telegraph lines along the track. As, however, this secondary circuit occurs only at the making and breaking of the telegraphic impulse, the length of the impulse affords no means of differentiation into an alphabet, and so a rapid series of impulses, caused by the vibrator of an induction coil, is made to produce buzzing tones of various duration representing the alphabet, and these tones are received upon a telephone instead of a Morse register. The diagram, Fig. 12,[1] ill.u.s.trates the operation.

[1] From "Electricity in Daily Life," by courtesy of Charles Scribner's Sons.

To receive messages on a car, electric impulses on the telegraph wire W, sent from the vibrator of an induction coil, cause induced currents as follows: Car roof R, wire _a_, key K, telephone _b c_, car wheel and earth. In sending messages closure of key K works induction coil I C, and vibrator V, through battery B, and primary circuit _d_, _c_, _f_, _g_, and the secondary circuit _a_, _h_, _i_, charges the car roof and influences by induction the telegraph wire W and the telephone at the receiving station.

In 1881 William W. Smith proposed the plan of communicating between moving cars and a stationary wire by induction (U. S. Pat. No. 247,127, Sept. 13, 1881). Thomas A. Edison, L. J. Phelps, and others have further improved the means for carrying it out. In 1888 the principle was successfully employed on 200 miles of the Lehigh Valley Railroad.

[Ill.u.s.tration: FIG. 13.--WIRELESS TELEGRAPHY, INTERNATIONAL YACHT RACES, OCTOBER, 1899.]

_Wireless Telegraphy_, or telegraphing without any wires at all, from one point to another point through s.p.a.ce, is the most modern and startling development in telegraphy. To the average mind this is highly suggestive of scientific imposition, so intangible and unknown are the physical forces by which it is rendered possible, and yet this is one of the late achievements of the Nineteenth Century. Many scientists have contributed data on this subject, but the principles and theories have only begun to crystallize into an art during the first part of the last decade of the Nineteenth Century. Heinrich Hertz, the German scientist, was perhaps the real pioneer in this line in his studies and observations of the nature of the electric undulations which have taken his name, and are known as "Hertzian" waves, rays, or oscillations.

Tesla in the United States, Branly and Ducretet in France, Righi in Italy, the Russian savant, Popoff, and Professor Lodge, of England, have all made contributions to this art. It will aid the understanding to say, in a preliminary way, that electric undulations are generated and emitted from a plate or conductor a hundred feet or more high in the air, are thence transmitted through s.p.a.ce to a remote point, which may be many miles away, and there influencing a similar plate high in the air give, through a special form of receiving device known as a "coherer," a telegraphic record. The "coherer," invented by Branly in 1891, is a gla.s.s tube containing metal filings between two circuit terminals. The electric waves cause these filings to cohere, and so vary the resistance to the pa.s.sage of the current as to give a basis for transformation into a record.

In March, 1899, Signor Guglielmo Marconi, an Italian student, then residing in England, successfully communicated between South Foreland, County of Kent, and Boulogne-sur-mer, in France, a distance of thirty-two miles across the English Channel. Signor Marconi used the vertical conductors and the Hertz-oscillation principle, and his system is described in his United States patent. No. 586,193, July 13, 1897.

His patent comprehends many claims, a leading feature of which is the means for automatically shaking the "coherer" to break up the cohesion of the metal filings as embodied in his first claim, as follows:

"In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a circuit through the contact, and means actuated by the circuit for shaking the contact."

The Marconi system of wireless telegraphy was practically employed with useful effect April 28, 1899, on the "Goodwin Sands" light-ship to telegraph for a.s.sistance when in collision twelve miles from land and in danger of sinking. It was also used in October, 1899, on board the "Grande d.u.c.h.esse" to report the international yacht race between the "Columbia" and the "Shamrock" at Sandy Hook, as seen in Fig. 13. Lord Roberts also made good use of it in his South African campaign against the Boers. According to Signor Marconi its present range is limited to eighty-six miles, but it is expected that this will be soon extended to 150 miles.

[Ill.u.s.tration: FIG. 13A.--THE COHERER.]

Marconi's receiving apparatus is shown in Fig. 13A, and consists of a small gla.s.s tube called the coherer, about 1 inches in length, into the ends of which are inserted two silver pole pieces, which fit the tube, but whose ends are 1/50 inch apart. The s.p.a.ce between the ends is filled with a mixture composed of fine nickel and silver filings and a mere trace of mercury, and the other ends of the pole pieces are attached to the wires of a local circuit. In the normal condition the metallic filings have an enormous resistance, and const.i.tute a practical insulator, preventing the flow of the local current; but if they are influenced by electric waves, coherence takes place and the resistance falls, allowing the local current to pa.s.s. The coherence will continue until the filings are mechanically shaken, when they will at once fall apart, as it were, insulation will be established, and the current will be broken. If, then, a coherer be brought within the influence of the electric waves thrown out from a transmitter, coherence will occur whenever the key of the transmitter at the distant station is depressed.

Mr. Marconi has devised an ingenious arrangement, which is the subject of his patent referred to, in which a small hammer is made to rap continuously upon the coherer by the action of the local circuit, which is closed when the Hertzian waves pa.s.s through the metal filings. As soon as the waves cease, the hammer gives its last rap, and the tube is left in the decohered condition ready for the next transmission of waves. It is evident that by making the local circuit operate a relay, in the circuit of which is a standard recording instrument, the messages may be recorded on a tape in the usual way.

[Ill.u.s.tration: FIG. 13B.--DIAGRAM OF THE TRANSMITTER AND RECEIVER.]

In Fig. 13B is shown the diagram of circuits. The letters _d d_ indicate the spheres of the transmitter, which are connected, one to the vertical wire w, the other to earth, and both by wires _c' c'_, to the terminals of the secondary winding of induction coil, c. In the primary circuit is the key _b_. The coherer _j_ has two metal pole pieces, _j j_, separated by silver and nickel filings. One end of the tube is connected to earth, the other to the vertical wire _w_, and the coherer itself forms part of a circuit containing the local cell _g_, and a sensitive telegraph relay actuating another circuit, which circuit works a trembler _p_, of which _o_ is the decohering tapper, or hammer. When the electric waves pa.s.s from _w_ to _j j_ the resistance falls, and the current from _g_ actuates the relay _n_, the choking coils _k k'_, lying between the coherer and the relay, compelling the electric waves to traverse the coherer instead of flowing through the relay. The relay _n_ in its turn causes the more powerful battery _r_ to pa.s.s a current through the tapper, and also through the electro-magnet of the recording instrument _h_.