386 NINETEENTH CENTURY. PT. III. 



then spells out the word York. This warns the man at 

 that station to turn the handle of his commutator, B', so that 

 the telegraph-wire, d, and the earth-wire, g, are joined to- 

 gether. Then the message can be sent. The man in 

 London turns his handle according as he wishes the current 

 to go. In Fig. 69 he has turned it so that the telegraph 

 wire, <:, is joined to the positive pole of the battery, and the 

 current will pass above ground along c d to the galvano- 

 meter A', turning the needle to the right, and will then go 

 back into the earth, and an equal amount is restored at/<? 

 to the battery. But in Fig. 70 the man has altered the 

 handle, and now the earth-wire, <?, is joined to the positive 

 pole, and so the current passes underground at ef, and out 

 at g, and entering the galvanometer on the left side, turns 

 the needle to the left, and goes back by the telegraph wire, 

 d c, to the battery. In this way he turns it from right to 

 left as he will, and spells out the message thus : Left, right 

 V = A ; left, right, left, left, ^ = L ; left, right, right J/ = W-, 

 left, \ = E; therefore J ; J^ 9 J^,J/; \; J^ J^; spells 

 * all well: 



It is not necessary to have a separate wire for every tele- 

 graphic station : one wire will do all the work so long as it 

 is only used by one man at a time, and it has now indeed 

 been found possible to send two separate messages at the 

 same time along one wire. 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 ; Bain's 

 electro-chemical telegraph writes down the marks on chemical 

 paper; while lately (1879) Mr. Cowper has invented a 



