So far back as 1838 this property was applied by Morse in America in the recording instrument which bears his name, and is now (with slight modifications) in general use not only in America but on the Continent. The principle of this instrument is exceedingly simple. Its essential parts are shown in Fig. 7; H is the handle, H _b_ the lever of the manipulator at the station A. The manipulator is shown in the position for receiving a message from the station B along the wire W. The handle H´ of the manipulator at the station B is shown depressed, making connection at _a´_ with the wire from the battery N´ P´. Thus a current passes through the handle to _c´_, along the wire to _c_ and through _b_ to the coil of the temporary magnet M, after circling which it passes to the earth at _e_ and so by E´ to the negative pole N´. The passage of this current magnetizes M, which draws down the armature _m_. Thus the lever _l_, pulled down on this side, presses upwards the pointed style _s_ against a strip of paper _p_ which is steadily rolled off from the wheel W so long as a message is being received. (The mechanism for this purpose is not indicated in Fig. 7.) Thus, so long as the operator at B holds down the handle H´, the style _s_ marks the moving strip of paper, the spring _r_, under the lever _s l_, drawing the style away so soon as the current ceases to flow and the magnet to act. If he simply depresses the handle for an instant, a dot is marked; if longer, a dash; and by various combinations of dots and dashes all the letters, numerals, etc., are indicated. When the operator at B has completed his message, the handle H´ being raised by the spring under it (to the position in which H is shown), a message can be received at B. [Illustration: FIG. 7.] I have in the figure and description assumed that the current from either station acts directly on the magnet which works the recording style. Usually, in long-distance telegraphy, the current is too weak for this, and the magnet on which it acts is used only to complete the circuit of a local battery, the current from which does the real work of magnetizing M at A or M´ at B, as the case may be. A local battery thus employed is called a _relay_. The Morse instrument will serve to illustrate the _principle_ of the methods by which facsimiles are obtained. The details of construction are altogether different from those of the Morse instrument; they also vary greatly in different instruments, and are too complex to be conveniently described here. But the principle, which is the essential point, can be readily understood.