disrupted by the slightest vibration. Therefore, a usable point of contact had to be found by trial and error before each use. The wire was suspended from a moveable arm and was dragged across the crystal face by the user until the device began functioning. In a crystal radio, the user would tune the radio to a strong local station if possible and then adjust the cat whisker until the station or radio noise (a static hissing noise) was heard in the radio's earphones. This required some skill and a lot of patience. An alternative method of adjustment was to use a battery-operated electromechanical buzzer connected to the radio's ground wire or inductively coupled to the tuning coil, to generate a test signal. The spark produced by the buzzer's contacts functioned as a weak radio transmitter whose radio waves could be received by the detector, so when a rectifying spot had been found on the crystal the buzz could be heard in the earphones, at which time the buzzer was turned off. The detector consisted of two parts mounted next to each other on a flat nonconductive base: a crystalline mineral forming the semiconductor side of the junction, and a "cat whisker", a springy piece of thin metal wire, forming the metal side of the junction Crystal: The most common crystal used was galena (lead sulfide, PbS), a widely occurring ore of lead. Varieties were sold under the names "Lenzite" and "Hertzite". Other crystalline minerals were also used, the more common ones were iron pyrite (iron sulfide, FeS2, "fool's gold", also sold under the trade names "Pyron" and "Ferron"), molybdenite (molybdenum disulfide, MoS2), and cerussite (lead carbonate, PbCO3) Not all specimens of a crystal would function in a detector, often several crystal pieces had to be tried to find an active one. Galena with good detecting properties was rare and had no reliable visual characteristics distinguishing it. A rough pebble of detecting mineral about the size of a pea was mounted in a metal cup, which formed one side of the circuit. The electrical contact between the cup and the crystal had to be good, because this contact must not act as a second rectifying junction, creating two back-to-back diodes which would prevent the device from conducting at all. To make good contact with the crystal, it was either clamped with setscrews or embedded in solder. Because the relatively high