Page:The American Cyclopædia (1879) Volume XV.djvu/641

 TELEGRAPH 613 B C D E- F G H I -- J K L LETTERS. M N - O - - P 8 --- T U V W X Y Z & NUMERALS. 5 17 19 6 8 PUNCTUATION. Period Comma Interrogation Exclamation Quotation Parenthesis The slightness of the difference, which cannot be avoided, between some of the signs, as in the and S, I and O, L and T, &c., exposes to mistakes, which in case of writing in cipher cannot be corrected, and not always when the message is perfectly understood by the opera- tor who sends it. Thus a merchant telegraphed from New Orleans to his correspondent in New York to protect a certain bill of exchange; the word "protect" was read as "protest," and involved serious consequences. What is known as the English telegraph is the result of the investigations and inventions of Wil- liam F. Oooke, whose attention was directed to this subject in March, 1836, when a stu- dent at Heidelberg, by witnessing an experi- ment performed by Prof. Moncke of causing the deflection of a magnetic needle by the electric current. In July of that year Cooke produced an experimental instrument, which he not long afterward took to England and sought to introduce on the Liverpool and Man- chester railway. He there became associated with Prof. Wheatstone, and the two united their labors to perfect the instrument. The first patent for an electric telegraph was issued to them on June 12, 1837. They employed five magnetic needles and coils, and either five or six wires, with a peculiar keyboard invented by Wheatstone, upon which were arranged the letters, and these were designa- ted in turn as any two of the needles ar- ranged across the centre of the board pointed to one and another of them. The apparatus underwent various modifications in the hands of its inventors, and was much simplified by the use of only two needles, and finally of only one, different letters being designated by the deflection of the needle to the right or to the left one or more times in either or both direc- tions. The swinging of the needle is checked by small pins fixed on the dial, so that the motions are rendered precise and clear. In this single-needle telegraph, each instrument has its own battery and wire. In case of acci- dent to the wire of one instrument, that of the other serves to keep up the communication. With each apparatus was formerly connected an alarum bell, the clapper of which was moved by a weight or spring connected with clock- work, which was released by means of an elec- tro-magnet. This is now generally abandoned, the sound made by the click of the needle against the pins being found sufficient. Wheat- stone introduced one very important feature in his electric telegraph, which is a local battery for working the alarum. It is brought into action by the deflection of a magnetic needle, the ends of which are thus placed in contact with the two wires of the second battery, and so close its circuit. The double-needle tele- graph is often used upon the railways of Great Britain, each needle having its own wire. The different signs are made by the movements of one or both of the needles. The needles upon the dial are moved by the messages sent as well as by those received, so that each opera- tor may see the signals he makes. In these needle telegraphs no record is made of the message by the instrument itself ; the operator observes the signs, and notes them upon paper as they succeed each other. With the English double-needle telegraph, employing two wires and two batteries and other apparatus at each station, an expert operator can send as many as 150 letters a minute ; but this is more than can be correctly read, the limit of which is about 100 letters a minute, and in actual prac- tice the number is somewhat less than this, or from IT to 24 words a minute. Operators ac- customed to the work do not require the let- tered dial for reading the movements of the needle. Of the numerous telegraphic inven- tions that soon succeeded those already named, Alexander Bain's are particularly worthy of notice. He was engaged in England as early as 1840 in producing a printing telegraph, and in 1846 patented what is known as an electro- chemical and registering telegraph, the princi- ple of which had been first applied to the pur- pose by Dyar in this country in 1827, and by Edward Davy in England in 1838. Mr. Bain brought his new telegraph to the United States in 1849, and it was brought into use on several important lines ; but after a lawsuit involving chiefly the use of the local circuit, the Morse interests forced a consolidation, and the Bain system had afterward but a limited use. The local circuit gave to the Morse sys- tem its great importance and value. On long lines of telegraph the wire offers such resis- tance to the passage of the current that its presence is detected only by delicate instru- ments, which however are capable of vibrating levers whose office is to open and close secon- dary or local circuits ; and these circuits being short, unlimited magnetic power may be ob- tained for recording or producing sounds. The Bain telegraph was essentially the same as that now called the "automatic." The revival of the system is due to recent discoveries in the arrangement of circuits, by which the rapidity of recorded electrical impulses through very long conductors has been made almost infinite. For recording, dots and lines are produced on chemically prepared paper, which is moved while damp at a uniform rate over a metallic roller; a fine wire, through which the line current passes, rests on the surface of the