TELEGRAMS, ELECTRIC. It is mainly owing to the labors of S. F. B. Morse, in the United States, and Cook and Wheatston in England, that electrical telegraphs owe their practical application.
In Cook and Wheatston's first ap paratus, five needles were arranged, with their axis in a horizontal line, the nee dles hanging vertically : each of the eleetro-inagnetie coils was connected with one of the long conducting wires at one end, and was united at the other with a common rod of metal, which joined to gether similar ends of all the coils. The current was transmitted from opposite ends of the wires, where an appropriate set of finger keys (5 pair) for making connec tion with the battery, was placed through two of the wires at once. placed the key was pressed down, the needles assumed various positions with respect to each other, and these were made to indicate signals according to entries in the signal book. The instruments at the two sta tions arc always reciprocating ; that is, at the ends of the line was placed en instru ment, a act of finger keys, and a voltaic battery, so that either station could re ceive or transmit a signal. By a beauti ful arrangement, a bell or alarm could be rung, when the attention of the clerk at the distant terminus was required. Mr. Cook obtained, in 1838, further ire provements on this apparatus without al tering its chief features.
The basis of this, and indeed of all elec tric telegraphs, is the fact discovered by CErsted, that when a magnetic needle is subjected to a current of electricity, the needle deviates towards a right angle to the position in which it stood originally. This was the simplest form of telegraph of Cook and Wheatston :—A magnetic needle was placed behind a vertical dial, its axis is prolonged out in front of the plate, and a second needle suspended to it, so that the latter moves similarly when the needle behind is impelled ; a coil of wire traverses above and below the inner needle, and when the ends of this coil are brought into contact with the poles of a battery, and the needle thus brought within the circuit, it is immediately de flected, and carries the outer needle along with it. This latter is the indicator. Stops are placed on each side of the needle to limit its motion on either side, and the letters are read off by a scale of arbitrary movements. Thus if the point of the needle move once to the right to express A, twice to the right might ex press B; once to the left, E., and so on. Dr. Stenheil constructed an electric tele graph between Munich and Bogenhausen, in 1837, in which he availed himself of the conducting power of the earth, thus saving the cost of erection, the earth oc cupying the place of the return wire.
In the same year Mr. Morse's invention was publicly tested. It was the first practi cal registering instrument, the various sig nals being traced on a strip of paper. In June,1844, the telegraph was constructed by him between Baltimore and Wash ington, through the aid afforded him by Congress, who advanced 30,000 dollars. Mr. Morse has taken out patents for im provements in his apparatus, the latest of whic4 was in 1848, for an " electro magnet, recording telegraph." To Mr. Morse is certainly due the credit of be ing the first who set up a practical mag netic telegraph invented in 1832.
.iforse's Teleg raph. This, the oldest telegraph of this kind in the United States, may be described as worked by a main circuit and distant battery.
The principle of this telegraph is based upon the temporary induction of a piece of soft iron with magnetism, by the cur rent of galvanism passing around it ; this piece of soft iron is called an electro -mag net, and it operates a walking-beam pen, to make mechanical marks upon a ribbon of paper carried along with a uniform motion, against the face of a grooved metal roller.
The batteries used are Grove's zinc and platinum, and two liquids. Any number of these may be used ; from 4 to 10 at termini are the usual number. To form the electric circuit, one end of a copper wire is attached to the end platina plate, and the other end of the copper wire to the zinc cylinder. A wire is not required to run round all the circuit—any metallic connection, such as brass plates, &e., may form part of it. The battery with the key attached, and the small table, we will suppose to be at the Philadelphia station, and the telegraph register io be at New-York. A wire runs from the pla ting plate up to the metallic binding screw connection on the small table above, and the other wire runs from the zinc, and is connected with the first wire by the me tallic connection of the register at New York. This forms the circuit. The key is fixed upon a pivot axis, to be gently pressed by the operator's fingers on the top of an ivory button. The circuit is now broken, and a small gap in the key above the wire from the battery shows the metallic connection to be open. By pressing upon the butt end of the key, its metal surface comes in contact with the metal termination of the wiro from the battery, and then the circuit is closed, and the electric fluid fleets along to the distant station, as in the present instance, New-York.