Telegraph The American Morse code or alphabet which is in general use on overland Morse telegraph lines in the United States and Canada is composed of dots and dashes and of combinations of dots, dashes and spaces. Letters made up partly of spaces are termed "spaced" letters. The let ters C and R are instances of spaced letters. (See illustration below). Dots, dashes and spaces are formed by the length of time dur ing which the key or other transmitting in strument may be held closed or open; the time of making a dot being taken as one, or one "time unit.") In length or duration a dash is theoretically equal to three time units. The space between the elements of a non spaced letter is equal to one time unit; the space between letters of a word is equal to three time units; the space between words, to five time units; the interval in spaced let ters is equal to three time units. The object of the framers of this alphabet in utilizing spaces in some of the letters was to minimize the length of the letters and thus practically to increase the speed of transmission by this alphabet. It was found, however, in auto matic telegraphy that the use of spaced letters increased the liability to errors, and hence an alphabet, known as the Continental or Universal Code, was adopted in Europe in which spaced letters are not used. This alphabet is now employed universally in Morse telegraphy outside of the United States and Canada. The American Morse and Continental Morse alphabets or codes are given on preceding page.
Morse Telegraph Apparatus Manual Transmitting Keys —As previously intimated, the characters of the Morse alphabet are formed by the manipulation of a suitable key. The key originally employed by Morse was a cumbersome piece of apparatus. The key now employed in the United States could not well be made lighter. Its construction will readily be grasped by reference to Fig. 4. A steel lever 1, is pivoted at 2. Metal legs 5, 5 pro ject through the desk or table, and are held securely thereto by the clamps shown. The right leg is connected directly to the metal base 6; the left leg passes through the base and is insulated therefrom by a hard-rubber bushing. On its top there is a cone-shaped cap, termed the anvil, carrying a small platinum contact point, 7. A small strip of metal ex tends out from the cap. At a point on its under side, directly above the contact 7, the lever 1 is provided with a platinum contact 8, termed the hammer. A curved strip of metal 9, the "circuit is pivoted on the base 6. When the circuit closer is pushed under the strip projecting from the cap 7, it closes the circuit, regardless of the opening between the anvil and the hammer. The lever 1 and the circuit closer 9 are supplied with hard-rubber finger tips, or knobs, by which they may be handled freely without danger of shocks. A spring adjustable by a set screw 4, normally lifts the lever 1 from the anvil. When the
operator is about to "send,” the circuit must be first pushed out from 7 so that the lever when operated may open and close the circuit; for it will be seen that when the ham mer is brought into contact with the anvil the circuit is closed at that point. Platinum is employed at all important contacts because of its durability and freedom from oxidation due to the sparking which usually occurs when electric circuits are broken. The manually operated Morse keys employed in Great Britain and Europe are practically similar to that shown here, but they are larger and heavier.
Morse Telegraph Relay.— The electro magnet which Morse first employed in teleg raphy weighed over 300 pounds. In 1844, how ever, the weight of this instrument had been reduced to 185 pounds. Within 15 years from that time many improvements had been made in the instrument and it then weighed hut little more than the modern main-line relay (typified in Fig. 5), about three pounds. As late as 1867 relays were wound to 1,100 ohms; the present standard resistance of this instru ment is about 150 ohms. In the case of what are termed "low resistance') relays the coils are wound to 37.5 ohms. These relays are utilized in a number of instances where many relays are employed on one circuit, as on rail way telegraph lines and the total reduction of resistance brought about by their use is found to effect a very beneficial result in the opera tion of the circuits in wet and foggy weather. The obvious explanation of this result is that, since the electric current seeks the path of least resistance, the lower the resistance of the wire circuit the less will be the tendency of the current to escape by the "leaks') to ground, where foliage, trees, etc., touch the wire.
These coils are covered by hard rubber sleeves. The armature 2 in this type of relay is a part of the iron lever 9'. These relays are adjusted in two ways; either by drawing the cores away from the armature by means of the screw 4, or by means of the retractile spring 6 attached to the armature, the tension of which is variable by the winding device 7. This winding screw is movable toward or from the relay coils by aid of the post 12 through which the supporting piece of 7 passes. The main line wires are connected to the screw posts 8, 8', from which small wires lead to the coil 1, 1'. The local, or sounder, circuit wires are brought to screw posts 11', 11, from which posts wires lead to the armature lever 2, and to the front contact 10. The object of the relay being to repeat or relay the signals passing on the main line to the sounder, the play of the armature lever (which latter is pivoted at 3, 3'), should not be large. This play is regulated by the front stop screw, that is, the stop next the coils, and by the back stop screw, which is insulated.