and joined to the line wire by means of a flexible cord. The round magnet has its two poles diametrically opposite, and the magnetic distribution is the same as in Duchemin's circular compass. On the lower thread a lid is screwed with a ring,

by which the telephone is hooked up when not in use; upper thread takes the cover, mouthpiece, and the vibrating diaphragm. The distance of the plate from the poles is regulated by inserting brass washers of suitable thickness.

The telephone so constructed forms a compact whole, rigid, and not easily put out of order.

Erection of Telephone Stations.-Fig. 52 shows the coupling up and connections necessary for two complete

telephone stations, batteries, transmitters, receivers, and bells. The number of elements necessary to work the bells varies with the distance, while that of the elements required for the microphone system varies very little with this distance, generally three Leclanché cells in series.

Milde's Telephone Station.-Without contradiction, simplicity, elegance, and cheapness, for small telephone stations, are combined in the apparatus shown in Fig. 53. The whole apparatus is movable, and comprises the transmitter—a D'Argy microphone, a round Bell receiver, call-bell, button, and automatic commutator. The battery — one Leclanché cell for each station-is fixed, and may be hung against a wall, or hidden in a corner of the room. In the most recent pattern it is hidden in an elegant bracket, used to stand the apparatus on. In the ordinary position, or when at rest, the apparatus stands on a table or bracket. A button B fixed underneath, Fig. 53, is thus lifted, and puts the bell in circuit. Pressing the button A, the right-hand station calls

up the left-hand station, which in its turn calls up the righthand station. The two interlocutors have then to take the apparatus by the handle, and by putting it to the ear automatically put the telephones in circuit.

The instrument is so made that when the receiver is put to the ear, the rectangular board of the transmitter comes near the mouth, on the side, and a little obliquely. When the conversation is finished, and the apparatus replaced on the table, communication with the bell is again established.

The whole thing is compact and light; the two stations and their batteries, with 60 yards of wire, are enclosed in a neat box, and make a charming present to give to young amateur students of electricity.

Telephone Elbow-rests.-In many of the combinations of private or central telephone stations, the caller has to hold the receiver to his ear, waiting for the reply. The annoyance of waiting, and the fatigue of the position, make the time often seem longer than it really is.

F

patience may be more easily exercised. By means of a metal arc and a catch, the height can be easily regulated to that of the speaker.

CHAPTER V.

ELECTRIC CLOCKS.

THE uses to which electricity may be put, for the indication and measurement of time, are of various kinds.

Sometimes it may be used to transmit at regular intervals: a signal or mechanical action to regulate and set the time of a clock or a series of clocks, each working independently in the ordinary way.

Sometimes it is itself the motor, which from a distributing centre works a number of dials situated at a distance.

Finally, it is sometimes the motor of the clock itself, where it replaces the spring or weights required to be wound up daily, weekly, or fortnightly.

In order to get rid of this necessity a system has been sought for capable of acting indefinitely while the battery lasts, and the patented variations and adaptations are almost without number.

Electric Butterfly Clock.-A battery capable of supplying a given quantity of energy, dependent upon the volume of liquid, its composition, the thickness of the zinc, &c., would very soon be exhausted if it had to furnish a current to give an impetus to each tick of the pendulum. But experience shows that this impetus is only required now and then.

In the clock shown in Fig. 55, Lemoine only gives this impetus at the moment when it is necessary in consequence of the decrease of the amplitude of the oscillation of the pendulum; a considerable saving of the battery is thus effected, which therefore lasts longer, while waste of electric energy is avoided.

This clock has an ordinary train of wheels worked by the