Fac Simile telegraphs constitute another, although less important branch of the art. These accomplished the striking result of reproducing the message at the end of the line in the exact handwriting of the sender, and not only writing, but exact reproductions of all outlines, such as maps, pictures, and so forth, may be sent. The fac simile telegraph originated with F. C. Bakewell, of England, in 1848 (Br. Pat. No. 12,352, of 1848).
The Dial Telegraph is still another modification of the telegraph. In this the letters are arranged in a circular series, and a light needle or pointer, concentrically pivoted, is carried back and forth over the letters, and is made to successively point to the desired letters.
Among other useful applications of the telegraph is the fire alarm system. In 1852 Channing and Farmer, of Boston, Mass., devised a system of telegraphic fire alarms, which was adopted in the city of Boston (U. S. Pat. No. 17,355, May 19, 1857), and which in varying modifications has spread through all the cities of the world, introducing that most important element of time economy in the extinguishment of fires. Hundreds of cities and millions of dollars have been thus saved from destruction.
Similar applications of local alarms in great numbers have been extended into various departments of life, such as District Messenger Service, Burglar Alarms, Railroad-Signal Systems, Hotel-Annunciators, and so on.
FIG. 12.—TELEGRAPHING BY INDUCTION.
For furnishing current for telegraphic purposes the dynamo, and especially the storage battery, have in late years found useful application. In fact, in the leading telegraph offices the storage battery has practically superseded the old voltaic cells.
Telegraphing by induction, i. e., without the mechanical connection of a conducting wire, is another of the developments of telegraphy in recent years, and finds application to telegraphing to moving railway trains. When an electric current flows over a telegraph line, objects along its length are charged at the beginning and end of the current impulse with a secondary charge, which flows to the earth if connection is afforded. It is the discharge of this secondary current from the metal car roof to the ground which, on the moving train, is made the means of telegraphing without any mechanical connection with the telegraph lines along the track. As, however, this secondary circuit occurs only at the making and breaking of the telegraphic impulse, the length of the impulse affords no means of differentiation into an alphabet, and so a rapid series of impulses, caused by the vibrator of an induction coil, is made to produce buzzing tones of various duration representing the alphabet, and these tones are received upon a telephone instead of a Morse register. The diagram, [Fig. 12],[1] illustrates the operation.
[1] From “Electricity in Daily Life,” by courtesy of Charles Scribner’s Sons.