HENRY AND THE TELEGRAPH. 2f'5 



was a satiirated solution of the sulphate of copper ; — crystals of the 

 sulphate being suspended in the liquid, for supplying the exhaustion of 

 the copper. The liquid on the zinc side was a very diluted sulphuric 

 acid. With this arrangement the oxygen evolved at the zinc surface 

 forms mainly a zinc oxide, which dissolved by the liquid into a sulphate 

 of zinc, is prevented from passing to the copper side of the partition, 

 and the hydrogen evolved at the copper surface combining at once with 

 the oxygen of the copper salt, forms water, and allows the free copper 

 to be deposited on its own plates : and Professor Daniell was able to 

 announce in a paper read before the Eoyal Society of London, February 

 11, 183G, "I have been led to the construction of a voltaic arrangement 

 which furnishes a constant current of electricity for any length of time 

 which may be required."* 



Although it is true that the electric telegraph may be operated by the 

 old form of battery — frequently renewed, (just as a good steam-engine 

 may be efficiently w^orked by an inferior and wasteful boiler,) and also 

 that a uniform current w^ell adapted to the telegraph may be obtained 

 from the magneto-electric machine, yet the "constant" battery has 

 proved a most valuable boon in xn-omoting the practical economy and 

 success of modern telegraphy. 



1837. Mr. William Fothergill Cooke and Prof. Charles Wheatstone 

 obtained an English patent June 12, 1837, (No. 7390,) for a galvanometer 

 or needle telegraph, very similar to the earlier one of Schilling, employ- 

 ing six wires and five indicating needles. At what date Prof. Wheat- 

 stone's attention was first directed to electrical signaling cannot now be 

 ascertained; but in 1834 he had undertaken by means of his ingenious 

 invention of the revolving mirror (capable of measuring the millionth 

 of a second), to determine the velocity of ordinary electricity through 

 half a mile of copper wire;t and a year or two later, through about four 

 miles of the same. Early in 1836, he had contemplated a telegraph which 

 with five needles, should give thirty signs. Mr. W. E. Cooke, attending 

 a lecture on electro-magnetic communication by Professor Muncke, at Hei- 

 delberg, March G, 183G, (as previously mentioned,) at which the telegraphic 

 apparatus of Schilling was exhibited, at once "conceived the idea." In 

 his " Statement of facts to the Arbitrators" in December, 1810, Mr. Cooke 

 declares : "Mr. Moncke's experiment was at that time the only one upon 

 the subject that I had seen or heard of. It showed that electric cur- 

 rents being conveyed by wires to a distance, could be there caused to 



* Phil. Trans. Boy. Soc. 1836, vol. cxxvi,p. 107. In the "gravity battery" of Cal- 

 laiid, and of Varley, the porous diaphragm is dispensed with by placing the lighter 

 liquid (u diluted solution of zinc sulphate) above the heavier liquid (a saturated solu- 

 tion of copper snl])hate); the separation being maintained by tlieir dilference of 

 speciiic gravity. In this arrangement the copper plate rests at the bottom of the cell, 

 and the zinc plate is supported at its top. 



t Philosoph. Travsac. of Boy. Soc. (read June 19, 1834), vol. cxxiv, pp. 1 83-589. In this 

 paper, Wheatstone says, that his lirst ineffectual attempt to discover a velocity of 

 electricity was made in 1830. "The method by which I then i)roposed to effect this 

 purpos(>, Avas announced in a lecture delivered by Dr. Faraday, at the Royal Institu- 

 tion, in June, 1830." (p. 583.) 



