The bracket is bent out of a piece of strip brass about one-eighth of an inch thick and five-eighths of an inch wide, according to the shape shown in the illustration. The bracket is mounted on a circular wooden base about three inches in diameter. The circular wooden blocks used by electricians in putting up chandeliers, called “fixture blocks,” will make a satisfactory base. An electrose knob of the typewriter type may be purchased from any good dealer in wireless supplies. It should be fitted with a threaded shank which will screw into a hole in the upper part of the bracket. The mineral is contained in a small brass cup mounted on the base below the end of the knob. Contact with the mineral in the cup is made by means of a fine wire spring soldered to the end of the adjusting screw. Moving the screw up or down will vary the pressure of the spring on the mineral and permit the most sensitive adjustment to be secured. The bracket is connected to one of the binding-posts and the cup to the other. [Illustration: Fig. 211.—Details of the Crystal Detector.] The detector shown in Figure 212 is of the type often termed a "cat-whisker," because of the long, fine wire resting on the mineral. It consists of a small clip, formed by bending a strip of sheet-brass, which grips a piece of galena. [Illustration: A Double Slider Tuning Coil.] [Illustration: A Junior Loose Coupler.] [Illustration: Crystal Detectors.] Galena may be obtained from any dealer in radio supplies. A piece of No. 30 phosphor bronze wire is soldered to the end of a short length of brass rod supported by a binding post. The other end of the rod is fitted with an electrose knob. This part of the detector is called the "feeler." [Illustration: Fig. 212 Details of the "Cat Whisker" Detector.] The detector is fitted with binding posts and may be mounted upon any suitable small base. The mineral clip is connected to one post and the binding-post supporting the "feeler" to the other. The tension or pressure of the end of the fine wire upon the mineral may be regulated by twisting the electrose knob so as to twist the rod. The different portions of the crystal may be "searched" for the most sensitive spot by sliding the rod back and forth. A somewhat similar form of cat-whisker detector is shown in Figure 213. It is provided with a cup to hold the mineral in place of a clip. The detector shown in Figure 214 is more elaborate than any of the others described so far. [Illustration: Fig. 213.—Another Form of the "Cat-Whisker" Detector.] [Illustration: Fig. 214.—"Cat-Whisker" Detector.]