Sir Charles Wheatstone (1802-1875), British physicist. Whilst studying acoustics and the theory of resonance of columns of air, he invented the concertina musical instrument in 1829. He invented the printing telegraph and the single- needle telegraph. He also worked on a commercial electric telegraph project which led to the construction of thousands of kilometres of telegraph lines. He popularised the use of the Wheatstone bridge, which had been invented by Samuel Christie, to measure resistance in electrical circuits. Wheatstone also studied optics, and invented the stereoscope for making three-dimensional photographic images.