Only particular sites on the crystal surface functioned as rectifying junctions, so a usable site was found by trial and error before each use; the operator would drag the cat's whisker across the crystal until the radio began functioning.
Only particular sites on the crystal surface functioned as rectifying junctions, and the junction could be disrupted by the slightest vibration. So a usable site was found by trial and error before each use; the operator would drag the cat's whisker across the crystal until the radio began functioning.