462
EXPOSITION AT VIENNA.
of the line to the station , into the ground. The current from g 1 , dividing equally between the two coils of the magnet /, passing in one direction through one and in the opposite direction through the other, would not affect that magnet.
It would, however, ring the bell at the station and attract the attention of the station-master, who would hasten to set the semaphore again at " arrest.” By pressing down the button a , he would bring the station battery in circuit. The current from this battery, added to the half of that from g 1 , circulating in the coil of magnet f, which is attached to the line, would overcome the contrary influence of the other half of the current from g 1 , which passes in the opposite direction through the other coil of /and the artificial resistance, to the ground; the magnet f would again be influenced to set the clock-work in motion and the semaphore would fall to " arrest.” The commutator, in passing, would, of course, restore the coils of the magnet f to their harmonious relations and place it again in communication with the ground, ready to be agaiii influenced by the current from the station.
This arrangement (i. e., the division of a current by passing it through the reversed coils of an electro-magnet, the wire from one coil leading out upon the line and from the other through a resistance equal to that of the line to the ground, in order that the magnet may not be influenced by its own, but only by a distant battery), is the principle of the # duplex telegraph of Mr. Stearns, now quite extensively employed in America.
A rough sketch of the commutator suggested is shown at Plate X.
A wheel, turning in the direction shown by the arrows and making a half turn for every signal, is added to the clockwork in the semaphore. It is furnished with sixteen insulated metal cogs, connected to each other by wires, as shown in the diagram. Above and to the left of the wheel is a semicircular band, on which are secured eight insulated metallic springs, which press against the cogs and connect them to wires leading in the different directions shown. The wire from spring No. 1 leads to the resistance coil and ground, No. 2 to the extra battery g 1 and ground, No. 3 to the ground