iron brake wheels, which it holds firmly.  The air cushion in the tube prevents the core being drawn up until it has fairly gripped the sides of the wheels.  The subsequent raising of the core therefore turns the wheels, raises the rack rod, and strikes the arc.  The feed is operated by the weakening of the magnetic field of the coil, which causes the core to lose its grip of the wheels, and allows the top carbon to descend.  The catch, L, Fig. 8, has a lateral play, and serves to engage in the teeth of the rack rod, so as to prevent its falling when being trimmed.  Each carbon when in position is held against two rectangular guide bars by the pressure of a wire spring—­see figure.  In this way the carbon is pressed against two parallel knife edges, and is therefore always in true alignment.  The action of the lamp is very simple, the working parts are few and solidly constructed, and the regulation, as exhibited by the lamps running in the galleries, is exceptionally steady.

The transmission of power plant consists of two 250 horse power dynamos—­C.E.L.  Brown’s patent—­the generator being driven by a vertical compound condensing engine of the same power, running at 180 revolutions.  The dynamo generator is a four-pole 600 volt direct current machine, series wound, and may be distinguished in the engraving next to the switch board; while the motor receiver connected to it, and erected in another portion of the Swiss section, is of exactly the same size and type.  The field, which is hexagonal in shape, is cast in two pieces, bolted together horizontally, the cross-sectional area of iron being 170 square inches.  The armature is cylindrical, and built up of flat rings stamped out of soft sheet iron, eight notches in the same being provided to fit over the arms of the spider keyed to the shaft.  The spider is in halves, which are bolted together longitudinally after the rings are in position.  It is Gramme wound, and measures over the winding 7 in. radial depth, 37 in. outside diameter, and 22 in. in length.  The current is collected by four brushes.  The fitting and mechanical build of the dynamos leaves nothing to be desired.  All the working parts of the dynamos and engines are turned up to gauge and template, so as to be interchangeable.  As an instance of this, the armature of the generator was built in the works, while the field magnets were being erected in the exhibition, and, on arrival, fitted in position perfectly, and ran at once without trouble.

The energy taken off on the motor shaft is close on 200 horse power, but varies according to the machines at work; the speed of the motor does not, however, vary more than 3 per cent., and the brushes need no adjustment.  About 6 ft. of shafting is coupled on in line with the motor shaft, and an extra plummer block fixed at the end.  This shafting carries at its extremity an additional 2 ft. pulley, the power being delivered by belting from these pulleys to two large pulleys on the main shaft.