Page:Popular Science Monthly Volume 88.djvu/813

 Popular Science MontJdy

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��One of the changes mentioned was the use of a powerful magneto magnet in place of the keeper or permanent magnet which is ordinarily used. The method of mounting is shown schematic- ally in Fig. 2. In using the magnet it must be mounted so that the lower sur- face A of the upper pole is above or level with the top of the armature E, so that the lines of force will penetrate the armature. A pole piece F can be used to extend the pole of the magnet. If used, it must be located over the center of the armature. It can be about y^"' square by %'' long. Its use can be determined by trial, since it does not always improve the operation of the instrument.

The magneto magnet can be obtained second hand for about 50 cents at a motor-cycle repair shop or a garage. If weak it can be re-magnetized for almost nothing. For a polarized relay of over 1,000 ohms resistance a few cents spent in obtaining a powerful permanent mag- net will be an excellent investment, as the commercial instrument of this re- sistance is beyond the means of the average experimenter.

When used as a relay, it is unneces- sary for the clapper rod to swing very far, so that the armature E may be lowered to close proximity with the ends of the magnet cores by means of two adjusting nuts. The distance can easily be determined by experiment. When used as a rectifier this distance need not be as small and can be adjusted accord- ingly. The bearing-screw R, Fig. i, should be adjusted to prevent any un- due play of the armature, but on the other hand, it must not be made tight enough to bind.

Inexpensive Stranded Aerial Wire

T is a well-known fact that stranded wire is preferred for aerials to solid wire, but it is not used much by ama- teurs since the cost is high. An inex- pensive stranded wire may be made, however, as follows :

Find the length of aerial wire needed and then cut five pieces of No. 20 bare copper wire that length. Lay them to- gether and about every two feet twist the strands twice. The resulting wire is of low resistance, high tensile strength and proves very satisfactory.

��Automatic Dead-End Switch

THE multiple-point switch, shown in the illustration, is equipped with small auxiliary switches to cut off the wire not in use on loose-coupler primar- ies or loading-coils. Most dead-end switches must be opened or closed inde-

���Wiring diagram of a multiple-point switch

pendently, but this one is operated by the movement of the multiple-point switch itself. It cuts off the primary in steps, immediately after you cut in less coil than the amount where each break occurs. Thus no switches are forgotten. The diagram explains its construction, and dimensions are not given, since they will vary somewhat, according to the spe- cific needs of the maker.

Avoiding Grounding in Running Metal Molding from Chandelier Outlets

TO run metal molding from outlets from which chandeliers are hung, and avoid grounding, the following method is suggested. Cut away the canopy as shown in Figure 2, and apply insulation between the canopy and separable, metal outlet box. Thi^^ pro- duces a neat appearance and is inex- pensive. — Joseph Fisher.

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��A Nfetal moldlni?. H New seimrable box C Partof ranoi)ycutaway IJ Insulatlni; material. E Remaining canopy..

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