CH. xxxv. THE AMERICAN TELEGRAPH. 361 



only used by one man at a time. Therefore at every station 

 there is a galvanometer to point out the message, a battery 

 to provide the current, and a commutator to change the 

 current ; but these are not joined to the general wire unless 

 they are being used. In Morse's American telegraph, which 

 is generally used on the Continent, the needle pricks holes 

 in a strip of paper, so that the message can be kept, and 

 Bain's electro -chemical telegraph writes down the marks on 

 chemical paper. But all these are only improvements of the 

 same principle by which an electric current going first one 

 way and then another acts on a magnetic needle. 



Chief Works consulted. Lardner's ' Cyclopaedia ' ' Electricity, 

 Magnetism, and Meteorology;' 'Annals of Philosophy,' New Series, 

 1822, vols. ii. and iii. ; 'History of Magnetism ;' 'Encyclopaedia Me- 

 tropolitana,' art. ' Electro-Magnetism ;' Faraday's 'Experimental Re- 

 searches in Electricity,' 1859; Tyndall's ' Faraday as a Discoverer ;' 

 Gladstone's ' Michael Faraday ; ' ' Nouvelle Biog. Universelle ' ' Am- 

 pere,' 'Oersted' ; Ampere, 'Observations Electro-dynamiques,' 1822 ; 

 Faraday, ' Various Forces of Nature ; ' Proctor, ' The Sun ; ' Her- 

 schel's ' Familiar Lectures ; ' Brande's ' Manual of Chemistry.' 



IT 



