436 WELLS'S NATURAL PHILOSOPHY. 



What is the 808, In what is known as the " Bain/' or 

 tuf "'chemical chemical telegraph, there is no magnet created, 

 telegraph? -^^^ q^ Small stecl wirc, connected with the 

 wire from the line, presses upon a roll of paper, moved 

 by clock-work. This paper, before being coiled on the 

 roller, has been dipped in a nearly colorless chemical solu- 

 tion, which becomes colored when an electric current passes 

 through it. By sending a current through the wire rest- 

 ing on the paper, we can stain it, as it were, in dots and 

 lines in the same manner as the last instrument em- 

 bossed it in dots and lines. 



809. The House's, or printing telegraph, 

 priiting tele- differs from the others principally in an ar- 

 ^*^ rangement whereby the message as transmitted 



is printed in ordinary letters, at the rate of two or three 

 hundred a minute. 



What iras the 810. The method first proposed for com- 

 method^'^pro- municatiug intelligence by electricity was by 

 posed? deflecting a compass needle by causing a cur- 



rent to pass along its length. 



Thus, if at a given point we place a galvanic battery, "and at a hundred 

 miles from it there is fixed a compass needle, between a wire brought from, 

 and another returning to the battery, the needle will remain true to its polar 

 direction so long as the wires are free from the excited battery ; but the mo- 

 ment connection is made, the needle is thrown at riglit %ngles to the direc- 

 tion of the current. The motion of the needle may thus be made to convey 

 intelligence. 



It is necessary, in convepng the wires from point to point, to support them 

 on the poles by glass or earthen cylinders, in order to insure insulation, 

 otherwise the electricity would pass down a damp pole to the earth, and bo 



lost. 



811. The idea that many persons have, that some substancp 

 cipfe T7influ- passes along the telegraphic wires when intelligence is trang- 

 ence pass along fitted, is wholly erroneous; the word current, as something 

 flowing, expresses a false idea, but we have no other term to 



messap 



communicated ? express electrical progression. We may, however, gain some 

 idea of what really takes place, and of the nature of the influence transmitted, 

 by remembering that the earth and all substances are reservoirs of electricity ; 

 and if we disturb this electricity at any given point, as at Washington, its pulsa- 

 tions may be felt at New York. Suppose the telegraphic wire a tube extend- 

 ing from Washington to New Tork perfectly filled with water; now, if one 



