ish Association papers on "Purkinje's Figures," and on "Bernouilli's Wind Instrument." These were followed by papers on "Chladni's Figures" (1833, "Philosophical Transactions"), and "Imitation of Human Speech by Mechanism" ("British Association Report," 1835).
The numerous analogies between the phenomena of sound and those of light early led him to the study of the latter subject. Here, again, his remarkable ingenuity as a mechanician came into play. He undertook to measure the velocity of electricity, and for this purpose he invented the method of revolving mirrors; in this way it was shown that the electric current travels at the rate of 288,000 miles per second. These results were published in the "Philosophical Transactions" in 1834. While engaged in these researches he observed that the sparks emitted from different metals under the influence of electricity differed from one another in color, "thus shadowing forth," says M. Dumas, "the discovery of the spectroscope." In the "British Association Report" for 1835 is a paper by Wheatstone on "Prismatic Decomposition of Electric Light," and in the Philosophical Magazine (1837) one on the "Thermo-electric Spark." He had been appointed Professor of Experimental Philosophy in King's College, London, in 1834, and in June, 1836, in his lectures on the velocity of electricity, which were illustrated by experiments with a circuit of copper wire nearly four miles in length, he proposed to convert this apparatus into an electric telegraph. At this time Wheatstone was not aware that Prof. Joseph Henry had five years previously transmitted signals by means of an electro-magnet through a wire more than a mile long, causing a bell to sound at the farther end of the wire. In May, 1837, Charles Wheatstone and William Fothergill Cooke (afterward knighted) took out a patent "for improvements in giving signals and sounding alarms in distant places by means of electric currents transmitted through metallic circuits." The first public line of telegraph was constructed on the Blackwall Railway in the following year.
While investigating the laws of light, Wheatstone was very naturally led to consider the phenomena of vision, and in 1838 he published in the "Philosophical Transactions" two papers entitled "Physiology of Vision" and "Binocular Vision." In the latter he explained the principles of an instrument invented by himself, the stereoscope. This invention was by no means the result of chance, but the fruit of profound study of the physiology of vision. In this matter Wheatstone's merit is unquestioned. Other papers on the phenomena of vision are, "Juxtaposition of Several Colors" (1844); a second communication on "Physiology of Vision" (1852); "Binocular Microscope" (1853); "Fessil's Gyroscope" (1854).
In the "Proceedings of the Royal Society" (1840) is an article by Wheatstone, on an "Electro-magnetic Clock," in which he shows how a number of clocks, situated at a distance from one another, may be act-
