Part 9 (1/2)

Now, supposing the switch (D'), in station 2, should be thrown over so it contacts with the wire (H') It is obvious that the current will then flow froh wires (H', C') and line (A) to station 1; then through wire C, switch D, wire E to the bell F, to the ground through wire G Froround to station 2, where it flows up wire G' to the battery, thereby co 85_ ILlustRATING LIGHT CONTACT POINTS]

The operator at station 2, having given the signal, again throws his switch (D') back to the position shown in Fig 84, and the operator at station 1 throws on his switch (D), so as to ring the bell in station 2, thereby answering the signal, which ain to be thrown over so they contact with the battery wires (H and H'), respectively When both are thus thrown over, the bells (G, G') are cut out of the circuit, and the batteries are both thrown in, so that the telephones are now ready for talking purposes

MICROPHONE--Originally this forenerally e distances a more sensitive instrument was necessary

LIGHT CONTACT POINTS--In 1877 Professor Hughes discovered, accidentally, that a light contact point in an electric circuit augmented the sound in a telephone circuit If, for instance, a light pin, or a nail (A, Fig 85) should be used to connect the severed ends of a wire (B), the sounds in the telephone not only would be louder, but they would be more distinct, and the first instru 86

[Illustration: _Fig 86_ MICROPHONE]

[Illustration: _Fig 87_ TRANSMITTER]

HOW TO MAKE A MICROPHONE--This instrument has simply a base (A) of wood, and near one end is a perpendicular sounding-board (B) of wood, to one side of which is attached, by wax or otherwise, a pair of carbon blocks (C, D) The lower carbon block (C) has a cup-shaped depression in its upper side, and the upper block has a sihtly held within these cups, so that the lightest contact of the upper end of the pencil with the carbon block,upon the sounding-board, h the telephone which is in the circuit

MICROPHONE THE FATHER OF THE TRANSMITTER--This instrureatly modified, and is now used as a trans the place of the pin (A), shown in Fig 85

AUTOMATIC CUT-OUTS FOR TELEPHONES--In the operation of the telephone, the great drawback originally was in inducing users of the lines to replace or adjust their instruet to throw them back, and all sorts of trouble resulted

It was found necessary to provide an auto out an instru the telephone on the hook, so that the actthe telephonethe instru the circuiting required for these i 87, a section of a transmitter

A cup-shaped case (A) is provided, m carries the carbon pencil (C) on one side and from the blocks which support the carbon pencil the wires run to binding posts on the case

Of course the carbon supporting posts o through the carbon pencil (C)

COMPLETE CIRCUITING WITH TRANSMITTER--In showing the circuiting (Fig

88) it will not be possible to illustrate the boxes, or casings, which receive the various instruments For instance, the hook which carries the telephone or the receiver, is hinged within the trans is all that it is intended to show

[Illustration: _Fig 88_ COMPLETE TELEPHONIC CIRCUIT]

The batteries of the two stations are connected up by a wire (A), unless a ground circuit is used The other side of each battery has a wire connection (B, B') with one terminal of the transmitter, and the other teroes to the receiver From the other terminal of the receiver is a wire (D, D') which leads to the upper stop contact (E, E') of the telephone hook A wire (F, F') frooes to one terminal of the bell, and from the other terminal of the bell is a wire (H, H') which makes connection with the line wire (A) In order to make a complete circuit between the two stations, a line wire (I) is run from the pivot of the hook in station 1 to the pivot of the hook in station 2

In the diagram, it is assumed that the receivers are on the hooks, and that both hooks are, therefore, in circuit with the lower contacts (G, G'), so that the transmitter and receiver are both out of circuit with the batteries, and the bell in circuit; but the moment the receiver, for instance, in station 1 is taken off the hook, the latter springs up so that it contacts with the stop (E), thus establishi+ng a circuit through the line wire (I) to the hook of station 2, and froh line (F') to the bell From the bell, the line (A) carries the current back to the battery of station (A), thence through the wire (B) to the transmitter wire (C) to receiver and wire (D) to the post (E), thereby co the circuit

When, at station 2, the receiver is taken off the hook, and the latter contacts with the post (E'), the transmitter and receiver of both stations are in circuit with each other, but both bells are cut out

CHAPTER XIII

ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING

DECOMPOSING LIQUIDS--During the earlier experiments in the field of electricity, after the battery or cell was discovered, it was noted that when a current was forases evolved from it A similar action takes place when a current of electricity passes through a liquid, with the result that the liquid is decoinal compounds Thus, water is coen, so that if two electrodes are placed in water, and a current is sent through the electrodes in either direction, all the water will finally disappear in the forases

MAKING HYDROGEN AND OXYGEN--During this electrical action, the hydrogen is set free at the negative pole and the oxygen at the positive pole A sien and pure hydrogen, is shown in Fig 89