TELEGRAPHS AND TELEPHONES.
Classes of Telegralhie Systems. —The transmission of intelligence tele graphically may be accotnplished either by means of optical or acoustical signals direct from station to station; or some other counnunicating media, such as air- or water-columns, electric conductors of wire, etc., are indi rectly used to produce signals between the despatching and receiving sta tions. Optical and acoustical telegraphs still find a limited application in the operation of railways (see page r79), for military and engineering uses, and for signalling at sea. Pneumatic telegraphs are to some extent in vogue for domestic service (the pneumatic bell). Hydraulic telegraphs, on the contrary, have not as yet passed beyond the experimental stage. All these systems, however, have been forced into the background by the electric telegraph and the telephone, NvIiich are to-day substantially the only methods in general use for transmitting intelligence to a distance.
First Electric-telegrafill Systems.—Although the idea had been broached much earlier, yet the first efforts to apply practically the wonderful speed of transmission possessed by electricity for telegraphic purposes appear to have been made by Le Sage of Geneva, who in 1774 constructed a tele graph-Iine formed of twenty-four insulated wires to the end of each of which was hung a pair of pith balls. When the opposite end of any of these wires was brought in contact with the prime conductor of an elec trical machine, the balls forming the corresponding pair were electrified and repelled each other. It was possible by this means to sig,naI each and any of the twenty-four letters constituting the French alphabet. Somewhat later Lomond improved upon the method of Le Sage by dispensing with all but a single wire and a shrgle pair of pith balls, and designating the desired letter by the amount of divergence of the balls. Following these primitive efforts, Reiser, Bockmann, and SaIva attempted to devise a signalling system based on the employment of elec tric sparks transmitted in a certain predetermined manner as to time and number. An apparatus by Salva operating, on this principle was shown in Iadrid in 179S. INIodifications of this plan were experimented with by Cavallo (1797) and Ronalds (rSt6), but led to no useful result. All these attempts were restricted necessarily to the then only known means of gen erating electricity—namely, by friction. They all proved impracticable and unavailing, for the reason that the static electricity produced by the frictional-electric machine is of such excessively hig,h pressure, or poten tial, that it is impossible to confine it by insulation to wires and to pre vent it from passing off to neighboring bodies.
The Uo/laic Pile,' discovered in ISoo, opened the way for a practicable system of electric teleg,raphy. The electrical current developed by the voltaic battery has sufficient strength to follow the longest and most cir cuitous course through metallic conductors (wires), and, on the other hand, its pressure is so low that it may be confined readily to the wires by the application of suitable insulating devices or coverings.
Siiinnzering's Systenz.—S3ininering of Munich (iSoS) endeavored to make use of the property of the voltaic battery to decompose water as the basis of a system of telegraphy. In Sommering's system " thirty five glass tubes closed at one end and filled with water were inverted over a similar number of gilded metallic strips which passed through the bot tom of a long and narrow ,g,lass trough or reservoir of water. This consti tuted the receiving apparatus Each of the tubes corresponded to some letter or numeral and was joined to the transmitting station by a separate wire soldered to the metallic strip underneath. The wires were insulated from one another, and after leaving the reservoir were bound into a single strand. At the sending station each wire was separately insulated and connected with a metallic terminal. To send a signal, it was only neces sary to bring the two poles of a voltaic pile to two of the terminals in ques tion. The current, passing- from one terminal, traversed its line wire to the voltameter at the receiving station, where it passed between the gilded metallic strips corresponding to the terminals touched by the poles, and returned through the line wire to the terminal of the other pole of the pile. When this was done, bubbles of hydrogen appeared at the metallic strip in communication with the neg-ative pole, and bubbles of oxygen at the other one. Thus two sig-nals were given simultaneously, of which the hydrogen took precedence. When it was desired to indicate only one letter, the positive pole of the battery was brought in connection with zero and the neg-ative pole with the letter to be transmitted. SOmmering- proposed to call the attention of the receiving station by liberating an alarm by means of the accumulated gas " (Prescott). The method of SOmmering proved too expensive and too 'slow to be of any commercial value, and in conse quence was never applied in practice. Only of late years has the chemical .effect of the voltaic battery received practical application in the chemical telegraph of Bain. (See p. 353.) Needle discovery of ism by Oersted of Copenhagen in 182o may be said to mark the date of the origin of the electric telegraph. The invention by Schweigger of the " multiplier " was an important contribution to its practical solution, since by its use there was obtained the power of causing the deflection of a magnetic needle by even the feeblest current. The earliest attempts to produce an electro-magnetic telegraph are to be credited to Atnpere in Paris (182o), Ritchie in London, and Schilling of Cronstadt in St. Peters burg (1832). It was not, however, until 1833 that Gauss and \Veber of Gottingen succeeded in introducing the first practical telegraph of this kind. These savans erected a line of telegraph between the physical cabinet and the observatory of the university in Gottingen.