INTENSITY OF CURRENTS. 



voltaic battery upon a wire of given length, will be increased in 

 the same proportion as the area of the section of the wire is 

 augmented. Thus if the diameter of the wire be doubled, the 

 area of its section being increased in a fourfold proportion, the 

 intensity of the current transmitted along the wire will be in- 

 creased in the same ratio. 



103. In fine, the intensity of the current may also be augmented 

 by increasing the number of pairs of generating plates or 

 cylinders composing the galvanic battery. 



Since it has been found most convenient generally to use iron as 

 the material for the conducting wires, it is of no practical import- 

 ance to take into account the influence which the quality of the 

 metal may produce upon the intensity of the current. It may be 

 useful nevertheless to state that, other things being the same, 

 the intensity of the current will be in the proportion of the con- 

 ducting power of the metal of which the wire is formed, and that 

 copper is the best conductor of the metals. 



104. M. Pouillet found by well-conducted experiments, that 

 the current supplied by a voltaic battery of ten pairs of plates, 

 transmitted upon a copper wire, having a diameter of four- 

 thousandths of an inch, and a length of six-tenths of a mile, was 

 sufficiently intense for all the common telegraphic purposes. Now 

 if we suppose that the wire instead of being four-thousandths of 

 an inch in diameter, has a diameter of a quarter of an inch, its 

 diameter being greater in the ratio of 62^- to 1, its section will be 

 greater in the ratio of nearly 4000 to 1, and it will consequently 

 carry a current of equal intensity over a length of wire 4000 

 times greater, that is, over 2400 miles of wire. 



105. But in practice it is needless to push the powers of trans- 

 mission to any such extreme limits. To reinforce and maintain 

 the intensity of the current, it is only necessary to establish at 

 convenient intervals along the line of wires intermediate batteries, 

 by which fresh supplies of the electric fluid shall be produced, 

 and this may in all cases be easily accomplished, the intermediate 

 telegraphic stations being at distances, one from another, much 

 less than the limit which would injuriously impair the intensity 

 of the current. 



106. Having thus explained the means by which an electric 

 current can be conducted from any one place upon the earth's 

 surface to any other, no matter what be the distance between 

 them, and how all the necessary or desired intensity may be 

 imparted to it, we shall now proceed to explain the expedients by 

 which such a current may enable a person at one place to convey 

 instantaneously to another place, no matter how distant, signs 

 serving the purpose of written language. 



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