XX11 



demy of Sciences at Munich in 1808 ; this involved a separate insulated 

 conductor for each letter and numeral, any two of which might be indi- 

 cated by a small evolution of gas from two corresponding gold points 

 immersed in a common fluid. A very similar system was suggested by 

 Prof. Coxe of Philadelphia in 1810, who proposed to indicate the signals 

 by the decomposition of some metallic salt. Prof. Schweigger of Erlan- 

 gen proposed to reduce the number of conductors in Sommering's tele- 

 graph to two, and to employ an electric pistol to call attention at the 

 receiving station. 



In relation to the dawn of practical electro-telegraphy, the names of 

 Proment in Prance, of G-auss, Weber, and Steinheil in Germany, and of 

 Morse in America, will immediately suggest themselves, but to Charles 

 Wheatstone is undoubtedly due the merit of having been the first to 

 render the electric telegraph practically available. In 1834, the year of 

 his appointment to the Professorship, he devised an experiment which at 

 once attracted the attention of scientific minds throughout Europe, and 

 ultimately had a large influence in determining the direction of his future 

 labours. His object was to ascertain the rate at which an electric wave 

 travels through a metallic conductor. Por this purpose about half a mile 

 of copper wire was insulated by suspension in the vaults under King's Col- 

 lege ; and three interruptions of this circuit were made by three pairs of 

 small brass knobs, with a small interval between them, placed in a 

 horizontal line at a few inches distance from each other, one being 

 near each end of the conductor, and the other one at its middle point. 

 It was presumable that the positive and negative terminal sparks pro- 

 duced by the discharge of a Leyclen jar through the insulated wire would 

 be absolutely simultaneous, but if any perceptible time were occupied by 

 the passage of the wave, the middle spark would occur later than the 

 terminal ones. To determine this a small plane mirror mounted on an 

 axis parallel to the line of sparks was made to revolve with great rapidity 

 by a train of clockwork. If any sensible angle were described by the 

 mirror during the passage of the wave, the middle spark would be seen 

 either above or below the line joining the other two, according to the 

 direction of rotation of the mirror. This in fact proved to be the case ; 

 and from the estimated amount of displacement and rate of rotation, the 

 velocity of transmission was inferred to be over 250,000 miles in one 

 second ; but from the nature of the observation the limits of error are 

 necessarily very wide. This experiment was subsequently repeated with 

 an extended circuit of nearly four miles, which was further utilized in the 

 transmission of electric signals by the deflections of a galvanometer- 

 needle. 



In 1836 Mr. W. P. Cooke having been struck, during a visit to 

 Germany, by the applicability of an electric telegraph devised by 

 Baron Schilling to practical and especially to railway purposes, brought 

 back with him on his return to London a working model of Schilling's 



