364 THE POPULAR SCIENCE MONTHLY. 



ish Association jjapers 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 under- 

 took 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 Re- 

 port " 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 tele- 

 graph. 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 natu- 

 rally 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 Wheat- 

 stone's merit is unquestioned. Other papers on the phenomena of 

 vision are, " Juxtaposition of Several Colors " (1844) ; a second com- 

 munication on "Physiology of Vision " (1852); "Binocular Micro- 

 scope" (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- 



