ELECTRIC BELLS.

alike as possible, or else to put the bell with the lowest resistance the furthest from the battery, so that the resistance of the line compensates for its lower resistance. If there are many bells, care must also be taken to provide sufficient battery power, the largest sized cells being used. The practice of splitting up a battery of smaller cells into two halves, and connecting the halves in parallel, is not advocated, unless absolutely necessary, it being far preferable to employ larger sized cells.

Push Buttons.-These are switches (see Figs. 285 and 286) for closing a circuit by means of pressure applied to a button. The button is applied to a spring so that when pushed in and released it springs back; thus the circuit is closed only as long as the button is pressed.

Pulls.-These are switches for closing a circuit when

pulled.

Magneto Bell and Generator.-Fig. 278 shows a small magneto bell and generator, there being also a switch hook at the bottom, since the generator is mainly used for telephony, which is the chief field of the magneto bell. The generator is, it will be seen, fixed in the body of the case, while the bell is on the lid. The hammer-head, projecting through a hole, works between the two gongs.

The apparatus required for signalling by the method men tioned above consists of two parts-the generator and the bell. The principle on which the generator acts is the same

ELECTRIC BELLS.

as that on which is based the action of all dynamos, and, in fact, the generator finds in the dynamo almost its exact counterparts.

The Electric Buzzer is a very useful instrument for use in places where the ringing of a bell would be an annoyance. It operates on the same principle as the electric bell and can be adjusted to emit a musical and pleasing hum instead of the ordinary ringing.

The direction of the current cuts no figure in this class of work; connect the opposite ends of the circuit to the opposite ends of the circuit to the opposite poles of the battery and the circuit is complete.

Wiring plans and specifications should be worked out by electrical engineers rather than architects or builders, as the problems of wastage of current and the danger to life and property are extremely difficult to work out under all the varying conditions.

"Diagrams" should be made showing in detail the connections actually required, and these should be provided at an early stage of any installation.

ELECTRIC BELLS.

Explanation of Technical Terms used in Electric-bell Work.

Battery.-The combination of cells which furnish the current of electricity for working the bells, indicators, &c.

Cell.-Each outer jar of the battery, with its two elements and exciting fluids constitutes a cell.

Circuit.-The wires, bells, indicators, batteries, &c., form. ing the path for the electricity.

Deflection.-The angle or number of degrees through which the needle of the detector moves during the passage of a current round the coils.

Earth return.-The use of the earth as part of the circuit.

Earth wire.-The wire from the bell, battery, &c., leading to the water or gas pipes.

ELECTRIC BELLS.

Fault.-Any break or interruption of the circuit by which some of the operations are interfered with.

Line.-The wire joining one station with another.

Line Battery.-The battery which is used to send the currents to line.

Local battery.-The battery placed near the bell or apparatus required to be worked which continues the ringing of the bell after it has been once started by the current from the line battery.

Local circuit.-The circuit through which the current of the local battery flows.

Metallic circuit.-The use of another wire for return instead of earth.

To connect up.-To join the bells, indicators and other apparatus included in the circuit.

To disconnect.-To remove the ends of the wires from the terminals of the instrument, thus cutting it out of the circuit.

To make" earth."-To connect the wire to earth.

A short-circuit.-A fault caused by two wires coming together so as to form a shorter path for the current, diverting the whole or greater part of it from its proper course.

To short-circuit a cell.-To join the terminals with a piece of wire.

To short-circuit an instrument.—To join the terminals of the bell, &c., with a piece of wire.

ELECTRIC PUMPS

Pumps suitable for all services are built to be driven by electric motors, and special designs have been made to cover the requirements of hydraulic elevator service, mine service, water works supply, irrigation purposes, fire protection, or in short any service where electric motive power can be used to advantage.

The great variety in style and size of these pumps now in successful use assures the extension and enlargement of the application of electric motors to all kinds of pumping machinery.

Fig. 287 shows a motor attached to a pump with govern. ing arrangement which is very simple in construction. The pulley of the switch is connected by a chain to a float resting upon the water in the tank, so that when the water falls the wheel is revolved until the starting point is reached, when it causes the switch arm to pass slowly over the contacts until the full current is cut in, and the motor runs at full speed. As the water rises, through the action of the pump, the pulley is turned in the opposite direction, finally making a quick break, shutting off the current and stopping the motor. This switch is positive in action, and cannot fail to work at all times and under all circumstances. It prevents the tank from overflowing or becoming empty through neglect of the attendant