Page:Popular Science Monthly Volume 91.djvu/970

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��Popular Science Monthly

��The center of the base must be determin- ed and a io-in. circle drawn. With a com- pass set at % in. from point to pencil, and starting from the top of the circle, twenty- five points are to be established on each side of the starting point, making fifty points in all, and each ^-in. distant from the next adjoining. Holes }/% in. in diame- ter are bored at each of these points, and at each of the lower corners. The box is

���Lever with its connections and knob for making contact with clips and the coils

then sand-papered and painted black.

When the box is dry the fifty paper fasteners are inserted in holes on the circle, and the binding posts are placed in the holes in the lower corners. The switch blade is shaped and placed as illustrated in Fig. 2. To facilitate the work of wiring, the baseboard is removed. The blade is electrically connected with the lower right- hand binding post with insulated wire having sufficient slack so as not to hamper the movement of the switch blade.

Fifty small coils, as shown in Fig. I, each having 25 turns 3 in. in diameter, are now made. One of these is connected between each pair of paper-fastener switch buttons, on the reverse side of base. That is, one end of the first coil is connected with the left-hand binding post, and the other end of the coil with the lowermost switchpoint on the left side of the circle. To this point is also attached one end of the second small coil, the other end of that coil being attached to the adjacent or second switchpoint. The remaining coils are similarly employed to successively con- nect adjacent points until a complete cir- cuit is established around the arc to the last switchpoint on the right, which is, however, not connected with the binding post on that side.

The wires are secured to switchpoints

��by taking two turns around the prongs or points of paper fasteners and then bending over the prongs, as is done when papers are bound together. The base is then screwed in place. All the wiring has been done on its reverse side.

The loading coil is placed in the circuit by connecting the aerial wire with right-hand binding post on the face of the base, while the primary of an inductive coupler is con- nected with the left-hand binding post.

For testing, a dry cell may be connected in series with a telephone across the binding posts. When the switchblade is revolved, a click should be obtained at each of the fifty contact points. Should the click not be obtained at any point, the connections at that point should be examined and firmly secured, or the small coil should be exam- ined to see that the magnet wire is not broken.

A coil made as described has been in constant use and has operated satisfac- torily. — -Charles E. Kalbach.

A Coating to Make a Battery- Box Acid Proof.

MELT together in an iron kettle 8 parts of wood tar and 14 parts of resin, and then stir in 10 parts of finely powdered brick dust. Apply this solution warm to the battery-box, after it has been well cleaned and sandpapered. — Edwin Jasper.

��A Water-Gage Glass Used for a Lead-in Insulator

THE diagram shows how a wall insulator may be made by combining a length of steam boiler water-gage glass with two



��Glass insulators and a boiler water-gage glass used for a lead-in insulator

old lighting cable insulators. A piece of No. 6 wire may be substituted for the brass rod . I f the glass tube is shortened .ordinary porcelain insulators may be used with good results. — Odis Reynolds.

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