Working in either direction, sextuples transmission is feasible between London and Brighton, London and Birmingham, and London and Bristol ; but qnadruplex is the limit to Liverpool. In one direction, however, to Manchester, even six circuits have been operated as an experiment. so that with two wires twelve circuits might possibly be worked, six in each direction.
The Pollen dSynehronoue "nit Vex system is the invention of Lieut. F. J. Patten, U. S. A., and depends for its operation upon the synchronous and uniform move ment of two or more electric motors placed at distant points. It is evident that an ordinary Siemens armature in a two-pole field must reverse its current at every half revolution. If by any means two such machines be caused to reverse their armature currents simulta neously, they would necessarily move in svnchronism. The system will be readily understood from the illustration. Fig. 6. which is a diagram of all the operative circuits, including two terminal stations. ln the two-line system a single synchronizing line is used for controlling a movement of electric motors, and may be used to synchronize the motors for any number of lines In the single-line system the synchronizing current is used both for synchronizing and telegraphing, without either function interfering with the operation of the other. For the sake of simplicity the two-line system is selected fordescription.
In Fig. 6. X and F represent two terminal stations of a telegraph line. The synchroniz ing line, L L. extends from the earth at X to at Y, reversing the polarized relays, P' and at these stations. At any intermediate point in the line, whether at For X, or midway between, is placed a revolving pole changer, the function of which is to constantly reverse a current on this line derived from the synchronizing battery, 9. This pole changer is driven by an electric motor having independent field and armature circuits, by which means its speed may be regulated and controlled ; it is shown in the middle of the diagram. The lamps, 11, are in the armature circuit in multiple are, and by turning them on or off, the speed of the pole changer may be varied, the field remaining of uniform intensity excited by the battery, 10. This pole changer sends rapidly reversed currents continuously to line, and maintains the polarized relays at X and Y in constant and rapid vibration. They nec essarily beat in syn chronism, and are re versed by every half revolution of the con trolling motor. These alternations sct the pace of as many ma chines as it may be de sired to place in cir cuit. Very little cur
rent is used for this purpose, the battery line on a one hundred mile circuit having only about 30 volts potential. The cur rent is necessarily very weak, and the vibra tion of the polarized relays is delicate but constant.
The armatures of these polarized relays drive a powerful vi brator in the same way that a relay ac tuates a sounder, the vibrator being placed upon a local circuit of low tension, and this is given sufficient strength and a suitable form to both rapidly reverse and convey the heavy currents of the motor armatures. These vibrators are shown at in the diagram, which is sufficiently clear to explain their operative parts. The polarized relay, as it'vibratos to and fro, place; alternately one side and the other of the vibrator in circuit, and its arma ture is rapidly and strongly pulled first against one contact point and then the other.
It being now understood how the regulator at some intermediate station keeps the polar.
ized relays in unison movement, and they in turn maintain the local vibrators in correspond ing unison movement, it will be explained how this system of devices maintains the motors at distant stations in synchronous rotation. The motors are shown at X and V by diagram circuits, M' and the fields, XS, are constantly and separately excited by the batteries, /" and while the armatures receive their current alternately in opposite direction from the batteries, ml in', at X, and ne= m' at Y, as the vibrator armatures move to and fro.
The motor armatures are of peculiar construction, and will continue in rotation when supplied with a current of rapidly reversed direction, the connections being such that a con stant polarity of the armature is maintained with reversed currents, provided the armature turns through a certain arc of the circumference at each reversal of the current. As the system is now used, they are so connected that they move one-fourth of the revolution at each reversal of current. The synchro nism is thus corrected automatic ally four times in each revolution; it may be made eight or twelve, or more, if desired. The spindles of the armature have secured to them revolving trailer arms carrying brushes which sweep over the seg mental distributors, s' and a'. They are shown flat in the diagram, for clearness, but are evidently at right angles to the spindles, which in practice are vertical. as shown in 1?ig. 7, which represents the machine in perspective.