Charles Wheatstone (1802-1875), British physicist. Wheatstone studied acoustics and the theory of resonance of columns of air, leading to his 1829 invention of the concertina musical instrument. He invented the printing telegraph (1841) and the single-needle telegraph (1845). He also worked on a commercial electric telegraph project which led to the construction of thousands of kilometres of telegraph lines. He popularised the Wheatstone bridge, invented by Samuel Christie, to measure resistance in electrical circuits. Wheatstone also studied optics, and invented the stereoscope (1838) for making three-dimensional photographic images. He was knighted in 1868.