Handy man's workshop and laboratory . eight as those supporting the tube. Fix thisblock lengthwise in the center of the baseboard. Procure a smallpermanent magnet of the horseshoe variety, and mount it on theblock in such a position that its north pole will be pointing directlyin front of and nearly touching the outside turns of the sec-ondary coil (Fig. 243), while its south pole will be opposite oneend of the tube. If the disk on the clockwork revolves fromright to left (as it ought), the south pole should be to the leftof the center of the tube and coils; if in the opposite direction, tothe
Handy man's workshop and laboratory . eight as those supporting the tube. Fix thisblock lengthwise in the center of the baseboard. Procure a smallpermanent magnet of the horseshoe variety, and mount it on theblock in such a position that its north pole will be pointing directlyin front of and nearly touching the outside turns of the sec-ondary coil (Fig. 243), while its south pole will be opposite oneend of the tube. If the disk on the clockwork revolves fromright to left (as it ought), the south pole should be to the leftof the center of the tube and coils; if in the opposite direction, tothe right. It is immaterial which pole is in front of the secondarycoil, as long as the remaining pole is in the proper relation to thedirection of the moving band, about to be described. The com-mercial instrument is fitted with two magnets, like poles adjoin- 304 HANDY MANS WORKSHOP AND LABORATORY slight as to be ing, and facing the center of the secondary coil, but the difference in effectiveness of this arrangement is Fig. 244—Winding the wire band We now come to the last, and if not properly made, the mostdifficult and exasperating part of the detector, the moving bandor rope of iron wire. To the uninitiated this has always been asource of great difficulty and annoyance, and though simplicityitself when made in the following manner, attempts at othermethods are almost sure to result in a bungling tangled mass ofstray loops and ends. The wire of which the band is made is No. 36 silk-covered, ironwire. Select a soft pine board % inch thick about 3 feet longand 4 inches or 5 inches wide. Drive two nails to a depth of ^2
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