HENRY AND THE TELEGRAPH. 267 



other clock ; so that by means of such discharges at one station, and. 

 by marking down the letters, figures, and signs seen at the other, any 

 required words could be spelt."* 



" He also made the trial with 525 feet of buried wire. With this view he 

 dug a trench fonr feet deep, in which he laid a trough of wood two inches 

 square, well lined both within and without with pitch 5 and within this 

 trough w^ere i>laced thick glass tubes through which the wire ran. The 

 junttiou of the glass tubes was surrounded -^dth short and wider tubes of 

 glass, the ends of which were sealed uj) with soft wax." This form of 

 conductor was not found to operate very satisfactorily, and the inventor 

 on theoretical grounds did not think such an arrangement adapted to 

 the instantaneous electrical transmission required by his system. 



Mr. Eonalds, in 1823, published a full account of his telegraph, t In 

 1871, very nearly half a century later, as Sir Francis Eonalds, he pub- 

 lished a new edition of this interesting work; and a review of it in 

 " Nature " gives this presentation of the scheme : " Sir Francis, before 

 1823, sent intelligible messages through more than eight miles of wire 

 insulated and suspended in the air. His elementary signal was the di- 

 vergence- of the pith-balls of a Canton's electrometer, produced by the 

 communication of a statical charge to the wire. He used synchronous 

 rotation of lettered dials at each end of the line, and charged the wire 

 at the sending end whenever the letter to be indicated passed an open- 

 ing provided in a cover ; the electrometer at the far end then diverged, 

 and thus informed the receiver of the message which letter was desig- 

 nated by the sender. The dials never stopped, and any slight want of 

 synchronism was corrected by moving the cover." | 



This very ingenious device of sj'nchronous rotation at the opposite 

 stations presents the earliest example of a dial telegraph, or of a letter 

 indicator employing but a single wire. About forty years later, or in 

 1855, this system was successfully applied by Mr. David E. Hughes, of 

 Kentucky, to a letter-printing telegraph of remarkable rapidity and ac- 

 curacy. § 



1828. " Harrison Gray Byar, an American, constructed a telegraph 

 in 1827-'28, at the race-course on Long Island, and supported his wires 

 by glass insulators fixed on trees and poles. By means of common elec- 

 tricity acting upon litmus paper he produced a red mark. The difference 

 of time between the sparks indicated different letters arranged in an ar- 



* Encydoi)a>.dia Britcuiuka, 7tli ed. 1H42, vol. viii, p. GG-2. — Stli ed. 1854, vol. viii, i). 027. 



] Descriptions of an Electrical Telefjrapli ; and some other Electrical Apparatus. By 

 Francis Koualds. 8vo. Loiidou, 182:3. 



XXature. London, Nov. 23, 1871, vol. v, p. .59. 



^A second type of dial telegraph Avas invented by Prof. Charles Wheatstone in 

 18o9, in whicli the dial (or index) was rotated step by step by means of successive 

 impulses of the current on an electro-niagnet, -which operated a toothed escapement 

 on the axis of the dial or index ; — the indicated letter or figure being stopped as long_ 

 as desired. In tins case, the character was determined solely by the number of 

 electric impulses transmitted. This system was in 184(i, made the basis of a highly 

 original letter-ininting telegra))h, by Mr. Royal E. House, of Vermont; i)receding that 

 of Mr. Hughes, as will be observed, nearly ten years. 



