410 THE ELECTRIC TELEGRAPH. 



have to regret that it was not employed in the Atlantic 

 cable. 



104. Charge and Distribution along the Wire. The measure- 

 ment of the distribution and charge in an insulated wire is 

 of as much importance as the measurement of its insulating 

 power. The distribution is independent of local faults in 

 the insulating covering, and depends intrinsically upon the 

 geometrical form of the insulator. By measuring the charge 

 of a given length of cable, and comparing the result with 

 the mean charge of the material employed, the electrician 

 has a means of determining, with the greatest certainty, if 

 the insulating material has the same thickness at every point 

 along and around the conductor. A knowledge of the capa- 

 city for charge of a cable is also of the greatest importance 

 in the event of a rupture of the conductor while the insulation 

 remains good. 



Dr. "Werner Siemens first explained the phenomenon of 

 static charge in a cable, having had his attention directed to 

 it by the retardation of signals on a subterranean line between 

 Berlin and Frankfort-on-the-Maine. 



He says, in his paper on this subject, that when the resist- 

 ance of the battery is very small in comparison with the 



Fig. 185. 



resistance of an uniform cylindrical cable, the tension of the 

 pole of the battery connected with one end of it remain un- 

 altered, even when the other end of the line is put to earth, 

 and that the tensions of different points along its length are 

 in proportion to their distances from the end which is to 

 earth. To explain this, let a c (Fig. 185) represent the line 

 wire, a b the tension of the electricity of the battery inserted 



