The main terminals of this machine are fitted on substantial insulating bases, fixed one at each end of the top yoke.  These connect to the external circuit by a heavy cable—­the machine being capable of developing 500 amperes—­and to the shunt circuit, and regulating resistance by small wires; while the two connections to the brushes are by four covered wires in parallel on each side.  This mode of connection is more flexible than a short length of heavy cable, and looks well, the wires being held neatly together by vulcanized fiber bridges.  The dynamo is a low tension machine, the field being regulated to give 65 volts when running the lamp circuits.

[Illustration:  Fig. 10.]

The illustration, Fig. 10, represents the automatic re-regulator—­C.E.L.  Brown’s patent.  Motion is imparted to the cores of two electro-magnets at the ends by the pulleys, W W1.  The cores have a projection opposite to the spindle, ab, which latter is screw-threaded.  By a relay one or other electro-magnet is put in action, and the rotating core, which is magnetized, causes rotation of the spindle by attraction, resulting in the movement of the contact along the resistance stops.  The relay is acted upon directly by the potential of the dynamo, and the variable resistance is included in the shunt field of the machine, so that changes in the potential, resulting from changes in load or speed, are compensated for.

The arrangements of the lamp circuits and the lamp itself may now be described.  The lamps are all run in parallel circuit, but are divided into groups of five, each group being controlled by a separate switch on the board—­Figs. 11 and 11A.  These switches are not in direct communication with the dynamo, but make that connection through a large central switch, S2, which therefore carries the whole current.  The returns from each group are brought to the connections seen between the two resistances, where the circuits may be disconnected if desired, and the main current then passes through the ammeter, A3, to the other terminal of the machine.  One of the smaller switches at the top, Fig. 11A, is directly connected with one terminal of the 20 horse power dynamo before mentioned, and the other side of the switch to the motor in the machine tool exhibit.  Also one of the switches in connection with the central switch, S2, is connected to the same motor, and therefore the latter may be run by either machine, or, in fact, any combination of machines, lamps, and motor be made as required.

The form of switch made by the Oerlikon Works is illustrated in Fig. 7.  Two thick semicircular bands of copper are screwed at one end to opposite sides of a square block which is turned round by the switch handle.  The block has a projection at each corner, and two strong, flat, stationary springs are attached to the framework of the switch and press on opposite sides of the block.  The ends of the springs engage in the projections and prevent the switch being turned round the wrong way, while the pressure of the springs on opposite sides forces the copper bands to take up a position exactly in line with the terminal contacts when the switch is closed, or at right angles to them when it is opened.