THE TELEPHONE.

5. In the telephone receiver the induction currents pro duce changes of intensity in the magnetic field.

6. In consequence of these changes in the magnetic field, the diaphragm of the receiver is thrown into vibration.

7. The vibrations of the diaphragm of the telephone receiver give rise to air waves, which are propagated to the tympanum of the ear.

Every time the human voice is used vibrations of the air are produced and the louder and higher the greater the number of vibrations-with each change of tone the diaphragm vibrates in sympathy.

How to Use the Telephone.

To call Central Office, give the bell crank one sharp turn; then take the hand telephone from the hook, place it firmly against the ear and listen for the operator, who should answer, "What uumber?" Give the operator the number of the subscriber desired, who will then repeat back your order, and may, to avoid errors and to expedite the service, ask for further information in relation to the station called for.

In talking, speak directly into the transmitter, with lips as close as possible to the mouth-piece. When you are through talking return the hand telephone to the hook, give the bell crank one sharp turn, to notify the operator that you have completed your conversation.

Speaking clearly and distinctly gives better transmission than shouting. It is obvious that the user is part of the "system" and by the proper use of his telephone can greatly promote the general efficiency of the service.

THE TELEPHONE.

Carbon Telephone.—This is a telephone transmitter based on the use of carbon as a material whose resistance is varied by the degree of pressure brought to bear upon it. Many carbon telephones have been invented-the Blake transmitter is one of the most noted.

Bi-Telephone.—This is a pair of telephones carried at the end of a curved bar or spring so that they fit the head of the person using them; one telephone is held against each ear without the use of the hands.

The Telephone Exchange.—This is the office to which telephone wires lead in a general telephone system. The value of a 'phone to each subscriber depends upon the number of other subscribers on the line, or more correctly speaking, on the number with whom a subscriber can be placed in direct communication within any part of city or county or state.

The Switch Board.-When a person becomes a subscriber to a telephone company, the telephone placed in office or residence is connected by means of a copper wire to a certain point on the switch board in the exchange, and to this same switch board all other wires entering this same exchange are also connected. Then a cord or loop having terminal plugs enables the operator at the switch board to "connect in" any two subscribers. This action on the part of the operator virtually creates a private line each and every time a connection is made.

NOTE.-The modern telephone exchange is practically the creature of accident. For, in 1877, in New Haven, Conn., a number of private elephone lines were so constructed that they all passed through one office, ihus minimizing the amount of labor required to test each new circuit and keep it in repair. A crude form of switch was used in making the tests, and, on one occasion, an employe all unconsciously so disarranged this switch that, in place of the two persons at the respective ends of a private line talking together, two private lines were connected in circuit and four points or stations provided with the means of communication.

THE TELEPHONE.

The subscriber, in ringing his bell, causes a current of electricity to pass through a small coil of wire with an interior core, which core, when electrified, attracts a small lever, and this lever, in moving, allows the above mentioned drop to fall. Consequently, when a person becomes impatient and rings the bell of his telephone long and hard, he does not startle the telephone office by the noise, as he might be led to suppose; the drop simply falls.

Under the streets of New York City there is a network of subways. The cables contain usually fifty-one pairs of wires, and are pulled through the three-inch subway iron pipe called a duct.

After each wire has been connected with the corresponding one in the other cable, hot paraffine is poured over the loose wires; a lead sleeve is slipped over the joint, each end of the sleeve being sealed with hot lead, thus making a water and air tight connection with the lead covering of each cable. Great care must be exercised to prevent the wires of the cable from becoming moist or damp, due to poorly connected joints, for there would then be electrical leakage, or the resistance of the wires would be reduced, as water saturated with impurities is a good conductor of electricity.

NOTE. The method of drawing a cable through a long stretch of subway between two manholes is quite ingenious. A man stands in the manhole with a bundle of short rods, about three feet in length, with brass ends so constructed that one will fit into another and stand a large amount of pushing or pulling without parting A rod is inserted in a duct; another one is then clamped on and pushed forward, this process of joining being continued until the first rod appears at the next manhole. The last rod has a small rope fastened to it, the latter being in turn joined to a No. 6 wire, which is made fast to the end of the cable. A man in the second manhole disconnects the rods and draws the rope and wire through. The latter is made fast to a windlass, and by this means the lead cable, weighing about six pounds per foot, is slowly unreeled and drawn through the duct.