☞ The instruments used are classed as indicator, type-printing, symbol-printing, or chemical-printing telegraphs, according as the intelligence is given by the movements of a pointer or indicator, as in Cooke & Wheatstone’s (the form commonly used in England), or by impressing, on a fillet of paper, letters from types, as in House's and Hughe's, or dots and marks from a sharp point moved by a magnet, as in Morse's, or symbols produced by electro-chemical action, as in Bain's. In the offices in the United States the recording instrument is now little used, the receiving operator reading by ear the combinations of long and short intervals of sound produced by the armature of an electro-magnet as it is put in motion by the opening and breaking of the circuit, which motion, in registering instruments, traces upon a ribbon of paper the lines and dots used to represent the letters of the alphabet. See Illustration in Appendix, and

Morse code

.