Charles Wheatstone was a physicist whose fertile, questioning mind produced numerous discoveries and inventions in the fields of optics, acoustics, electricity, and telegraphy.
Wheatstone was born in Gloucester, England, to a family of musical instrument makers and dealers. He had no formal education in science. He was apprenticed to an uncle in 1816 as a musical instrument maker, and invented the concertina in 1829. His musical background led Wheatstone to experimental studies of acoustics, which in turn led to his appointment as professor of experimental physics at King's College, London, in 1834. Wheatstone held this position for the rest of his life, although he seldom lectured, concentrating instead on research in electricity and optics.
Wheatstone's contributions to acoustics included the kaleidophone, a device that produced a visual demonstration of sound vibration. He also made important discoveries about plate vibrations and vibrations in columns of air. In the field of optics, Wheatstone invented the stereoscope, which demonstrated how two pictures could be visually combined to create the illusion of depth and three dimensions. He anticipated the development of spectroscopy with his 1835 paper showing that the spectra of spark discharges differed according to the metal used for the electrode. Wheatstone also invented a polar clock, which used the angle of polarization of light to determine the time of day.
In the 1830s Wheatstone turned to the study of electricity. He used a rotating mirror in 1834 to make the first measurement of the velocity of an electrical current through a wire. (The same apparatus, by Wheatstone's suggestion, was later used to measure the speed of light.) These experiments, combined with his early interest in acoustics, led Wheatstone to speculate on the possibilities of sending messages along the wire using the electric current. At this point, Wheatstone was approached by William F. Cooke (1806-1879), an Englishman who had joined the East India army at the age of 20 in 1826 but who had been forced to resign his commission because of ill health. In 1835 Cooke had observed a demonstration of an electric telegraph, and, his imagination fired, returned to England in 1836 to devote himself to telegraph design. He turned to Wheatstone for advice, and the two formed a partnership. They patented their five-needle telegraph in 1837, constructed a demonstration line the following month, and installed the first working commercial electric telegraph for the Great Western Railway in 1838.
Although Cooke and Wheatstone persistently quarreled about claims of who actually invented their telegraph, they remained partners. Cooke concentrated on business affairs, while Wheatstone continued development work on the telegraph for many years. In 1840 he brought out the first of his many types of letter-showing dial telegraphs; in 1841 came the type-printing telegraph; then he introduced an automatic transmitting and receiving system. Wheatstone also studied submarine telegraphy, experimenting with an actual line in 1844 in Swansea Bay.
Wheatstone made important contributions in the field of electicity as well. He improved early versions of the dynamo. He recognized the great theoretical and practical importance of Ohm's law, and spread knowledge of it in England, where it was little known at that time. He invented the rheostat (an adjustable resistor), and popularized a method of accurately measuring electrical resistance that had been invented by Samuel Christie (1784-1865) but became known as the Wheatstone bridge.
Wheatstone was also an accomplished cryptographer, and invented a machine called the Playfair cipher to create indeciperable secret messages. Wheatstone received numerous honors for his scientific accomplishments. He married in 1847 and had five children. Wheatstone was knighted in 1868 and died on a visit to Paris in 1875.