954 



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 



INSULATOR 



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. 



