NATURAL PHILOSOPHY. 127 



The amount of business which a -well-conducted office can perform 

 is immense. Nearly seven hundred messages, exclusive of those for 

 the press, were sent in one day over the Morse Albany line, and, a. 

 few days after, the Bain line at Boston sent and received five hundred 

 communications. Another office with two wires, one five hundred, 

 the other two hundred miles in length, after spending three hours in 

 the transmission of public news, telegraphed, in a single day, four 

 hundred and fifty private messages, averaging twenty-five words 

 each, besides the address, sixty of which were sent in rotation, without 

 a word of repetition. The instruments cannot be worked successfully 

 without skilful operators, good batteries and machines, and thorough 

 insulation of the conductors. The expense of copper wire, which was 

 at first used, has caused it to be superseded by that of iron, which is 

 found to answer the purpose as well, though the wire in this case must 

 be of increased size. About 300 pounds of iron wire are required to 

 a mile. The cost of construction, including wire, posts, labor, &c., is 

 about $150 per mile. The average performance of the Morse instru- 

 ment is to transmit from 8,000 to 9,000 letters per hour. 



In the majority of electric telegraphs in actual use, batteries com- 

 posed of heterogeneous metals, chiefly zinc and platinum, moistened 

 by a liquid or liquids, are employed for the generation of force. The 

 earth itself has been made to furnish a supply of electric force ; in 

 other words, a single pair of zinc and copper plates have been buried 

 sufficiently below the surface to be in the wet subsoil, when the earth, 

 saturated with water, represents the sand saturated with acid- water of 

 an ordinary battery cell. By this means a current of low intensity 

 can be obtained, even when the plates are miles apart. The earth 

 acts as the return wire to any given number of distinct wires, without 

 in the least affecting the regularity of the action of any of them. 



The only constant and economical battery which is used in the 

 United States is Grove's, of cups of zinc with strips of platinum in an 

 earthenware or porcelain cup, which cup is filled with nitric acid, 

 which is placed inside of the zinc cup, in a tumbler containing diluted 

 sulphuric acid. The main battery on a line (from 30 to 50 cups) 

 requires renewing only once in every two weeks, and daily in local 

 batteries of two or three cups. 



Messages passing from one very distant point to another have 

 usually to be rewritten at intermediate stations ; though by an im- 

 proved method the sea-board line has in good weather transmitted 

 communications direct between New York and Mobile, a distance of 

 nearly 1,800 miles, without intermediate re-writing. By the Cincin- 

 nati route to New Orleans, a distance of nearly 2,000 miles, the news 

 brought by an Atlantic steamer at 8 o'clock, A. M., has been tele- 

 graphed from New York to that distant point, and the effects produced 

 on the market there returned to New York by 11 o'clock, A. M. 

 The Congressional reports from Washington are usually received 

 simultaneously in Baltimore, Philadelphia and New York ; and all 

 that is necessary at the intermediate stations is the presence of an 

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