C V Boys' radio-micrometer, with outer casing removed, 1907.
© Science Museum / Science & Society Picture Library
Made by the Cambridge Scientific Instrument Company. C V Boys was an experimental physicist renowned for devising a way of making delicate quartz fibres which he used in measuring instruments. The radio-micrometer introduced in 1887 was the most sensitive detector of heat radiation available at the time. He hoped to be able to heat radiation from the star Arcturus, but it was not sensitive enough. However, it could detect radiation equivalent to that from a candle at a distance of hundreds of metres.