In the construction of his telegraph, Dr. Steinheil made a capital discovery. He found that the conducting power of the earth might be made to occupy the place of the return wire. MI that is necessary is, that the wire which connects the two ends of the metallic conductor with the earth, shall be carried to a sufficient depth below the surface ao as to be always in contact with moist earth or with water : and that it shall be at this point attached to a plate or other piece of metal, of about two or three feet superficial. For the ordinary Voltaic battery, Dr. Steinheil substituted the magneto-electric machine ; in which, according to Faraday's great discovery, the electric current was derived by induction from a permanent magnet.
Tho electric telegraph invented by Prof. Morse, of America, has led to a large amount of controversy, a claim having been put in for him as the first actual inventor of a practical electric telegraph in 1S32, while on board the packet-boat Sully. The Abb6 Moigno states that a Mr. Jackson wrote to the Acad6inie Francaiee, affirming that he had, in 1839, communicated this plan to Mr. Morse, while returning together from Europe to America, on board the Sully. Even admitting, however, the claims of either party, it would only show that they did not think sufficiently well of their scheme to enter upon it until nearly three mouths after the first English patent for an electric telegraph bad been sealed, and the practicability of such an apparatus demonstrated in England. The first really official letter on the subject from Professor Morse, is dated September 27, 1837. Cooke and Wheatstone's first patent for an electric telegraph was sealed three months before this, namely, on June 12, 1S37. The difference between this telegraph and the preceding suggestions and contrivances was very great. The ex periments of these gentlemen had been proceeding for a long time previously, 80 that when in June, 18.37, their patent was obtained, it was not for an arrangement of doubtful practicability, or of a form to be perfected only after repeated trial. On the contrary it was, within a few months after the date of the patent, put up and brought into actual and daily use. Some of its details have since been simplified, and the modes in which the electric current is made to give the required indications have been greatly varied ; but the great features and prin ciples of their first invention remain unchanged, and not only so, but they form an essential part of nearly if not quite all the later tele graphs of other inventors.
The telegraph exhibited by Morse in September, 1837, was essen tially a registering instrument, the various signals being traced on a strip of paper. The plan appears to have been the following :—an electroanagiet was so placed as to be within attracting distance of an armature fixed to the shorter arm of a lever, of which the longer end carried a pencil projecting sideways from it, and pressed lightly against a sheet of paper. This paper, by a contrivance analogous to that of Dr. Steinheil, w•as made to travel slowly beneath the pencil. So long as no attractive power was exerted by the electromagnet, the pencil would continue to trace a straight line as the paper moved onwards ; but on momentarily.msking the circuit with the battery, the armature was drawn to the electro-magnet, and the pencil, carried by theeinn of the lever upwards, made an angular mark, like the letter V reversed, on the paper. These angles might either be joined in groups, by
rapidly succeeding completions of the circuit, or they might be sepa rated by longer or shorter spaces of straight line. The nine digits were represented by corresponding numbers of angles, and these were combined so as to form all possible numbers. A short space inter vening between two or more successive groups, denoted that they must be taken together to forum a total of two or more places of digits ; while a longer apace showed the actual completion of one number and the commencement of the next.. All the necessary words were represented by various numbers, as arbitrary signs, a previously arrauged dictionary being used for their interpretation. This plan had also been proposed by Mr. Rouble, to simplify the working of his telegraph.
In the telegraph erected by Professor Morse. in IS44, between Baltimore and Washington, a different mode of recording the signals was adopted. The use of the pencil was found objectionable, from its so frequently requiring fresh pointing, and from the risk of breakage. The same arrangements were retained in regard to the paper, but it was made in its course to pas.s over a roller having a groove around it. The long arm of the lever carried a blunt steel point, standing over the groove in the roller. When therefore the arm of the lever was depressed, by the attraction of the magnet upon the armature, the deal point pressed the paper into the groove, and produced an indenta tion. If the attraction were momentary, a depressed point was pro clerk at the distant terminus was required, was either direct or indirect In its action. lu the first case the attraction exercised by a horso-ahos piece of soft iron, rendered temporarily magnetic by the galvanic cur• rent, was made to draw an armature, likewise of soft iron, towards It, and by this action impel a small hammer against a bell In the second form of &Lamm, fig. 4, the movement of the armature merely released duced ; but if the action were continued for a longer time, a lengthened depression was the result, as the paper was drawn on. The combina tions of these two kinds of marks denoted the various letters and figures. Thus, dot and dash . — is taken to signify a; — . to signify b; — . — . for c ; . d ; . for e ; and so on. This is called the dot and dash code. Fig. 5 shows the arrangement of what is called the aymbol-printing telegraph : a is the armature attached to the lever which carries the steel point. The ribbon of paper is drawn slowly off from its roller r, by a train of clockwork in the box c, which drives two gripping rollers g. In its passage the paper goes over a brass roller I., containing the groove. If while the paper is thus being drawn over the roller 14 the clerk at the communicating station were by means of a common telegraph key or handle to transmit the current for an instant, the armature would be momentarily drawn down, and the steel point would mark the paper with a depressed dot. The spring would raise the arm the moment the magnet had ceased to act. But if, instead of transmitting only a momentary current the communica ting clerk were to continue the transmission for a abort time, the arm would be pulled down during that time, and the point would indent a line in the paper.