Charge detectors: A hard rubber rod and a lucite rod are placed upon needle stands. When charged, they can detect the presence of like charges by a repulsion, and unlike charges by an attraction. The rubber rod acquires a negative charge when rubbed by cat's fur, and the lucite rod acquires a positive charge when rubbed by a silk handkerchief.
|Box on 021-13A
|acrylic rod and a piece of silk