Cambridge Instrument Co. Ltd. Campbell Variable Mutual Inductometer, England. A precision laboratory instrument designed for the accurate measurement and calibration of mutual inductance, based on the Campbell method. Featuring decade multiplier dials (×100 and ×10), terminal selectors, and a large direct-reading scale calibrated in microhenries (absolute), the instrument was used in electrical standards laboratories and research work. Housed in a polished wooden case with engraved ebonised panels, it represents high-grade British scientific instrument manufacture. Early to mid-20th century, c.1920s–1940s.
