in Magnetism and Electricity. 83 



wire was terminated with a metal plate inserted in the moist 

 ground. This physicist also pointed out that the resistance 

 offered by the earth to the propagation of the current along the 

 wire might be reduced to such an extent as to be quite insensible 

 when compared with that of the double metallic circuit; so that 

 not only was one-half of the wire economized, but even the re- 

 sistance that such a mixed circuit of earth and wire presented 

 was diminished by one-half. 



92. The explanation of this singular and important fact, as 

 given by Steinheil, was that the conducting-power of the earth, 

 though very inferior when compared with that of the metals, yet 

 its bad conductivity was more than compensated for by the im- 

 mensity of its section. This interpretation of the earth's action 

 naturally led to the opinion that the electric current, after tra- 

 versing the whole length of the telegraph-wire, returned through 

 the earth back to its origin at the battery, in the same manner 

 as if the chain of earthy particles extending between the distant 

 electrodes had been confined in an insulated tube of large dimen- 

 sions. The difficulties, however, which encumbered this hypo- 

 thesis when the distance between the electrodes became consi- 

 derable, have led many physicists to abandon it as being incon- 

 sistent with certain well-ascertained facts. 



93. The present view of the earth's action in relation to tele- 

 graphic circuits, as supported by Gauss*, De la Rivet, Walker J, 

 and many others, is, not that the earth conducts the electricity 

 from the distant end of the wire back to its origin at the battery, 

 but that the earth acts as a vast reservoir of neutral electricity, 

 into which the positive and negative currents from each of the 

 insulated wires are absorbed, in the same manner as a discharge 

 of static electricity is received into the ground. 



94. In the course of an elaborate series of experiments on the 

 propagation of electric currents in the earth, M. Matteucci made 

 the curious observation that, when the distance between the elec- 

 trodes at each extremity of the insulated wire was very small, the 

 resistance of the terrestrial bed increased, up to a certain point, 

 in proportion to its length, according to the recognized law for 

 ordinary conductors; but when the distance between the elec- 

 trodes exceeded thirty yards, the resistance of the earth gradually 

 diminished until at a distance of a few miles it finallybecame null§. 



95. The only explanation which I have as yet met with of this 

 singular limitation of the earth's resistance is that of De la Rive, 



* Traite de Telegraphie Electrique, by M. l'Abbe Moigno : Paris, 1852, 

 chap. 3. 



f Treatise on Electricity, by A. De la Rive, vol. iii. p. 446. 

 X C. V.Walker's 'Electric Telegraph Manipulation,' p. 3/. 

 § Annates de Chimie et de Physique, 1851, vol. xxxii. p. 248. 



G2 



