Harper's Electricity Book for Boys

by Joseph H. Adams

When the wire is in place a drop of hot paraffine will hold the end so that the wire will not unwind. The ends of this spool-winding should be made fast to heavier wires, which are run through small holes in the tube (A) and project out at the end, as shown at F F. The magnet, with its wire-wound spool on the end, is then pushed through the hole in A until the top end of the rod is slightly below the edges of the cup (E), so that when the metal disk (D) is laid over the cup (E) the space between the magnet and disk, or diaphragm (D), is one-sixteenth of an inch (see [Fig. 5]). Put some shellac on the magnet, so that when it is in the right place the shellac will dry and hold it fast.

The cap (B) holds the disk (D) in place, and protects the spool and its fine wire from being damaged and from collecting dust. After giving the exterior a coat of black paint and a finishing coat or two of shellac, the receiver will be ready for use.

The original telephone apparatus was made up of these receivers only—one at each of a line in connection with a battery, bell, push-button, and switch. On a window-casing, or the wall through which the wires passed, a lightning-arrester was arranged and made fast. Using receivers only, it was necessary to speak through the same instrument that one heard through, and for a few years this unhandy method of communication was the only one possible. Then the transmitter was invented.

Plan of Installation

Many of these single-receiver lines are still in use, and as they require but a small amount of constructive skill a diagram of the wiring and the plan of arrangement is shown in [Fig. 6].

At the left side, R is the receiver at one end of the line and R 2 that at the other, line No. 1 being a continuous wire between the two receivers. When the boy at R wishes to call his friend at R 2 he uses his push-button (P B), and the battery (B B) operates the electric bell (E B 2) at the other end. In order to have the bell connections operative, the switch (S 2) must be thrown over to the left when the line is “quiet,” while the switch (S) should be thrown to the right. With the switches in this position the boy at either end may call his friend at the opposite end.

With the switch (S 2) thrown to the left (the position it should be in, except when talking over the line), the boy at the other end pushes his button (P B), first throwing switch S to the left. This makes connection for the battery (B B), and the circuit is closed through wires that join line No. 1 and line No. 2 at 1 and 2. The branch lines to the bell (E B 2) join the main lines at 3 and 4, through switch S 2, when the bar is thrown to the left. The circuit being complete, the batteries (B B) at one end of the line ring the bell (E B 2) at the other end of the line.

In the reverse manner, when the switch (S) is thrown to the right, the boy at the opposite end rings the bell (E B) by pressing on the button (P B 2), first throwing switch S 2 over to the right. If the boy at the left is calling up the boy at the right, the switch (S) should be thrown to the left, and he keeps ringing until the other operator throws switch S 2 over to the right. If now he has the receiver (R) up to his ear he can hear the vibration of the bell (E B 2) ringing through the receiver (R) at his end of the line. But when the boy summoned to R 2 takes up the receiver and places it to his ear, he throws switch S 2 over to the right side, and the boy at R leaves switch S over on the left side. This brings the lines into direct connection with the receivers in series. Be careful, when setting up this line, to have the batteries (B B) in series with B 2 B 2; otherwise there would be counter-action. The carbon of one cell should be connected with the zinc of the next cell, and so on.

Another receiver is shown at [Fig. 7]. The tube (A) and the cup are turned from one piece of wood, and the cap (B) from another piece. The length of the receiver is five inches, and the cap is two inches and a half across. The shank, or handle, through which the magnet is passed measures one inch and a quarter in diameter.