R. C. Browne.

A relay, carefully made according to the following directions, will prove a serviceable and extremely sensitive apparatus, suitable for many experiments in wireless or line telegraphy. The general construction is shown in Fig. 1, A being a piece of brass 1/2" x 1/4" and 61/2" long. It is bent in a vice as shown, the several angles being made as accurate as possible. Drill a 1/4" hole at a, which should be countersunk to receive the head of a brass screw, which holds the rod to the base, and another 1/4" inch hole at b. Drill 1/8" or 3/16" holes at c and d, which should be threaded to receive the thumb-screws e and f. See that the threads are the same in the hole as on the thumb-screws, the latter being the top screws from two binding posts, though brass machine screws may be used. The thumb-screw e should have a small piece of platinum soldered to the end, and the end of f should be covered with a piece of thin cardboard or rubber. The rod A is then screwed to the center and at one end of the base board B, which should be of hard wood 7/8" thick, 5" wide and 7" long.

For the magnet M there will be needed a piece of soft Norway iron C, 11/2"x1/2"x3/16. Drill three 1/8" holes h through it, one in the center and one 1/8" from each end. The hole in the center is threaded to receive the 3/16" machine screw D. The cores E are round, soft bar iron, 3/8"diameter and 21/16" long. In one end of each core drill holes, and thread them to receive a machine screw (g, Fig. 2).

After the cores are wound with wire they are fastened to the ends of the iron yoke C by these screws, thus forming a horseshoe magnet. Another way of fastening the cores to the yoke is to have the core pieces 1/4" longer, file down this extra length so that it will snugly fit the hole in the end of the yoke, and rivet firmly in place.

The cores being prepared, they are fitted at each end with round, hard rubber or fibre washers F, 3/16 thick and 1" in diameter, the hole in the center being 3/8 ". These washers are held in position by shellac or glue, thus forming two spools for holding the wire. The wire should be No. 36 cotton covered magnet wire. First cover the cores with three thicknesses of firm writing paper laid on with shellac. Bore a small hole in the rubber washer, on the yoke end, to receive the inside end of the wire, about 3" being left outside for connections. Wind the wire in even layers until the coil is nearly 1" in diameter. Coat each layer with shellac, and use great care to prevent kinks or breaks in the wire. One coil is wound in the opposite direction to the other, so that the poles will not be the same. Cover the outside of the coils with a layer of dark-colored paper or binding leather, both for appearance and protection ; then fasten to the yoke, and connect the inside ends of each coil. The magnet is then complete, and should be placed in position on the brass standard A, as shown in Fig. 1. A compression spring H, about 1/4" long, is fitted over the screw D, between the frame A and the yoke of the magnet. This allows the position of the magnet to be adjusted. The outside ends of the coils are carried through two holes bored in the base-board to the screws holding the binding-posts, which have been placed one in each corner of that end of the base-board, as shown in Fig. 1.

Fig. 1.

Fig. 2.

The armature or moving lever next demands our attention. Exceptional care must be taken in making it, as it is a very important part of the instrument. Obtain the works of an old clock of the square frame kind. These may generally be obtained from any clock repairer for the asking, the writer having secured about a dozen works recently at one place. Cut out with a knife-blade file that part of the frame having the bearings for the balance wheel (see J, Fig. 3). Save the balance wheel K, Fig. 3, shaft and bearings, to form the pivot for the armature. With a flat file smooth the edges of the pieces of the frame, and then bend them as shown at L, Fig. 3. Use care to have the centers of the bearings N exactly the same height above the base-board. Drill 1/8" holes in the parts resting on the base, to receive the screws O.

Remove the rim and spokes of the balance wheel, and cut a slot in the brass hub P, into which solder the wider end of a wedge-shaped piece of sheet brass R, 1/16" thick, 3/8" wide at the base, \" wide at the top, and H" long. At a point directly opposite the cores in-the magnet drill a hole in the piece R, and rivet on a piece of soft iron, T (thick stove-pipe iron will answer), 3/8/" wide and 11/2" long. Under the head of the rivet twist a short piece of steel wire, the end projecting to form a small hook, to which is attached the spring S. Mount the armature on the base-board so that the iron armature, T, will be directly opposite the cores of the coils and the shaft of the balance wheel moves easily but not loosely on the bearings N. Mark the point at the top of the lever R, where the thumb-screw e touches, and solder a small piece of sheet platinum, being sure to get it on the proper side of the lever.

The regulator for regulating the tension of the spring S, which holds the lever away from the magnets, is easily made. A large binding post, U, is placed as shown in Fig. 1, with the hole parallel to the armature and the post a little to one side of the center. Through the hole in the post put a piece of brass wire to one end of which has been soldered a round head so that it may be carefully turned. Make a small, light spring, S, by winding No. 30 brass wire around a wire nail, with a hook at each end. One end is placed on the hook of the armature and the other is fastened by a short length of silk thread to the brass wire in the binding post. To adjust the tension, turn the wire in the binding post, winding or unwinding the thread until the correct tension is obtained, then fasten with the screw in the binding post. Two binding posts are screwed to the remaining corners of the base-board, one of them being connected by No. 14 or 16 covered wire to the brass frame A, the other to one of the bearings N, holding the pivot R. These connecting wires are carried through holes bored and grooves cut on the under side of the base-board.

Fig. 3.