Popular Science MontJdy 



785 



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. 



f. 



A Nfetal moldlni?. 

 H New seimrable box 

 C Partof ranoi)ycutaway 

 IJ Insulatlni; material. 

 E Remaining canopy. . 



J/" 



?^s 



B- 



Fig. 1. 



Fi2.2. 



