Part 12 (2/2)

below the center of the circles to allow for D, and for the pin-point which supports the magnetic needle, the poles of which should be in the line pa.s.sing through the center of the coils. The method of cutting the hole, H, through C, will depend upon the tools at your service.

D is the front edge of an adjustable table, like that explained.

(Index.) It is 4-1/4 in. wide. It supports the magnetic needle which is inside of E.

E is the outside of a gla.s.s-covered compa.s.s. (See App. 67 for details.) The needle should not be over 1 in. long.

CHAPTER XIV.

TELEGRAPH KEYS AND SOUNDERS.

APPARATUS 118.

[Ill.u.s.tration: Fig. 92.]

_192. Telegraph Keys._ Fig. 92. Telegraph keys are merely pieces of apparatus by which the circuit can be conveniently and rapidly opened or closed at the will of the operator. An ordinary push-b.u.t.ton may be used to turn off and on the current, but it is not so convenient as a ”key.”

Fig. 92 shows a side view of a simple key. C is a metal strip about 3/4 in. wide and 4 or 5 in. long. At the left end it is fastened to the base with a screw, A. Another screw, X, serves as one binding-post. Y is another screw binding-post. W is a short wire, used to regulate the amount of spring to the key. This is done by moving W to the right or left. If the current enters at X, it will pa.s.s along C and out at Y, when C is pressed down. By moving C up and down according to a previously arranged set of signals, messages can be sent by means of the electric current. (See telegraph alphabet.) This apparatus is not a good one where the line is to be run with a ”closed circuit battery,” or where it is to be used very often. It will do, however, for places where a push-b.u.t.ton would be too tiresome to use. The right end of C is curved. This curve serves as a handle. D and E are wires leading from X and Y.

APPARATUS 119.

_193. Telegraph Key._ Fig. 93. The base is 5 4 7/8 in. The key, C, is made of two thicknesses of tin. It is made into a strip 5-1/2 3/4 in., then the front end is bent up for a handle, as suggested in Fig.

92, the front end being above the base so that it will not touch the strap, D, unless it is pressed down. C is fastened to the base by a screw, H, which also binds one end of the copper wire, C W. About 3/4 in. from H is placed X, which is a screw-eye binding-post. Under C is the wire, W, which is used to regulate the amount of spring in C, by moving it forward or backward. S I shows the position of a screw-eye, or of an ordinary screw put into the base through C. The hole in C should be made so that C can move up and down easily around the screw. This is used to make a click when the key is allowed to spring up. The downward click is made when C strikes D at each depression.

[Ill.u.s.tration: Fig. 93.]

The Strap, D, is made of tin. It is 4 1/2 in. before bending up the right end a little. It is fastened to the base by the screw, F, and by the other binding-post, Y. Its right end is raised enough to allow the arm, E, to pa.s.s under it, but it must press down well upon E when E is forced toward F.

The Swinging Arm or Switch, E, is also made of tin, and measures, finished, 4-1/2 1/2 in. Its front end should be bent up a little for convenience in handling it. (See Fig. 92.) E is pivoted at G by a screw, which also binds the wire, C W. Fig. 24 shows another way to make the pivot and connection.

194. Operation. See Fig. 99 for the details of the connections of a home-made telegraph line. When you are using the line and telegraphing to your friend, the switch, E, of your instrument must be open, as in Fig. 93, and the corresponding switch on his instrument must be closed; that is, the circuit must be opened and closed at but one place at a time. As soon as you have finished, your switch must be closed. He will open his and proceed. When you have both finished, both switches must be closed. If your friend left his switch open, you could not call him over the line, as no current could pa.s.s into his sounder.

195. Batteries. As the circuit has to be left closed for hours and perhaps days at a time, so that either operator can call the other, a closed-circuit battery is necessary. (See App. 9.) A dry cell, Leclanche, or other open-circuit cell would not be at all suitable for a telegraph line, as it would soon polarize. Large Daniel cells, which are 2-fluid cells like App. 7, or gravity cells (App. 9) are the best for your line.

APPARATUS 120.

_196. Telegraph Sounder._ Fig. 94. The wood-work consists of 2 parts; the base, B, is 6 4 3/4 in., and the back, A, is 6 5 1/2 in. A is nailed or screwed to B.

The Magnet, M, is fully described in App. 85. M is held firmly to A by cord or wire, which should pa.s.s around it near the poles and at the curved part. The wire should pa.s.s through small holes in A, and be tied at the back. Wire nails driven into A at the sides of M will keep it from moving about. The wires from the magnet coils are led to two spring binding-posts, X and Y.

[Ill.u.s.tration: Fig. 94.]

197. The Armature, C, is made of a narrow piece of thin iron, about 5-1/2 1/4 1/8 in. It may be made by bending up 3 or 4 thicknesses of tin into that shape. This is the part which will be attracted by M, when the current pa.s.ses, and which will make the clicks by which the message can be read. (See telegraph alphabet.) There are many ways by which C can be held near M. The figure shows how it can be done entirely with 1-in. wire nails. At the right end of C two nails are driven into A above and below C. They are just far enough apart to allow the left end of C to be raised and lowered without binding; in other words, these nails make a pivot for C to swing upon, and they help to support it at the same time. The left end of C must not quite touch the poles of M when the current pa.s.ses, because the residual magnetism would keep C from dropping back into place. To adjust the armature, pa.s.s the current through M, hold C so that it will not quite touch the poles, then drive in the upper nail, 2. Put another nail, 1, below C, so that M will not have to lift C more than 1/8 or 3/16 in. Try the nails in different positions until C quickly rises and falls when the circuit is closed and opened. A nail, 3, driven in front of C, will keep its right end in place. No springs are needed, as gravity acts upon C instantly, bringing it to the lowest position as soon as the current ceases to flow.

198. The Battery will depend upon how much you want to use the sounder.

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