272 HENRY AND THE TELEGRAPH. 



calico immediately over tlie cylinder. On every completion of the cir- 

 cuit at the transmitting station, a blue mark was thus imprinted on the 

 moving cloth by the electrical decomposition, and the succession of 

 marks of diflering lengths and intervals formed the system of signals. 

 This telegraph was found to work satisfactorily through eighteen hun- 

 dred yards of wire fence.* 



1846. Mr. Alexander Bain, of Edinburgh, obtained an English patent 

 for a galvano-chemical telegraph, which while exhibiting considerable 

 ingenuity in its mechanical devices, imitated very closely in its chemical 

 record the previous system of Smith. " The chemical solution preferred 

 for the preparation of the paper consists of sulphuric acid and a solution 

 of prussiate of potassa.'' t 



1849. Prof. Samuel E. B. Morse, of Kew York, obtained an American 

 patent for a galvano-chemical telegraph, also very similar to that of 

 Smith, employing like him a single circuit, and specifying, among sev- 

 eral metallic salts which might be used, solutions of iodide of potassium, 

 of iodide of tin, and of acetate of lead, with nitrate of potassa. The in- 

 ventor added : "I wish it to be understood that I do not confine myself 

 to the use of the substances I have mentioned, but mean to comprehend 

 the use of any known substance already proved to be easily decomposed 

 by the electric current." | 



III. — TELEGRAPHS BY GALVANO-MAGNETISM. 



Meanwhile the rapid awakening of attention among physicists to the 

 magnetic relation of the galvanic current, and the production of the gal- 

 vanometer, at once indicated a new and promising method of signaling 

 to a distance by galvanic agency. 



The Galvanometer. — In 1820, Hans Christian Oersted, professor of nat- 

 ural philosophy at Copenhagen, announced through various European 

 journals his discovery that if a straight conjunctive wire through which 

 a galvanic current is passing "be placed horizontally above the mag- 

 netic needle and i)arallel to it . . . the needle will be moved, and 

 the end next the negative side of the battery will go westward. . . . 

 If the uniting wire be placed in a horizontal plane under the magnetic 

 needle all the effects are the same as when it is above the needle, only 

 they are in an opposite direction." § 



Although the directive influence of a galvanic conductor on a mag- 



* Practical Mcchaiuc and Engineers' Magazine, June, 1846, vol. i, 2d series, pp. 239, 240. 



i English 2mtent of A. Baiu, Dec. 12, 1846, No. 11480. 



X American patent of S. F. B. Morse, May 1, 1849, No. 6420. 



^ Thomsou's Annals of riiilosopluj, Oct. 1820, vol. xvi, pp. 274,27.5. (Also, Journal 

 de Physique, etc. 1820, vol. xci, pp. 72-76; Annales de Chimie et de Physique, 1820, vol. 

 xiv, pp. 417-425; BihUotheque Unirerselle des Sciences, etc. 1820, vol. xlv, pp. 274-284; 

 Annales Generales des Sciences Phi/siques, 1820, vol. v, pp. 259-264; Gilbert's Annalen 

 der Physik, 1820, vol. Ixvi, pp. 29:)-;304; Scliweiggev's Journal fiir Chemie und Physik, 

 1820, vol. xxix, pp. 275-281; Giornale Arcadico di Scienze, etc. 1820, vol. viii, pp. 

 174-178; Brugnatelli's Giornale di Fisica, etc. 1820, pp. 335-342.) 



