of the Electric Force traversing Interposed Media. 187 



terloo-bridge a leaden pipe, 170 feet long, and three-fourths 

 of an inch internal diameter, through which was drawn an 

 insulated copper wire, 1 80 feet long, one extremity of which 

 being soldered to the inside of the end of the pipe, this end 

 was sealed with fused metal, and to its external surface was 

 soldered a copper wire of the same length as the former; 

 round the tube, at its orifice, was twisted a copper wire ten 

 feet long. The insulated wire being connected with a con- 

 stant battery of one pair of elements in contact with one pole 

 of an exceedingly delicate galvanometer, (constructed by Mr. 

 E. M. Clarke of the Lowther Arcade,) the other pole of the 

 galvanometer was brought successively in contact with the ex- 

 tremities of the uninsulated wires. The deflexion was greater 

 when the current passed along the wire connected with the 

 orifice of the tube, (although here the contact was not so 

 good,) than when it passed along that soldered to the sealed 

 extremity. 



Again, the uninsulated wires being connected with separate 

 galvanometers, so as to allow the current of electricity to pass 

 along either of the uninsulated wires alone, or to be distributed 

 between both, it was found (as well as could be determined by 

 transposing the galvanometers,) to have divided itself into two 

 equal currents flowing along both wires. 



From the first experiment we may infer that a current of 

 electricity passes with greater facility along the surface of a 

 metal than through the interior of its mass, although we can- 

 not hereby infer that it could not pass through the interior of 

 the metal, when this is the only road open for its transit*. 



To the experiments with phosphorus it might be objected 

 that its capability for conducting an electric current is due to 

 the presence of water, of which some have supposed that it 

 could not be entirely deprived, although the experiments of 

 Sir H. Davy, wherein he obtained hydrogen and oxygen from 

 sulphur and phosphorus by heating them in contact with po- 

 tassium and sodium, and by submitting them to the electrolytic 

 action of a powerful galvanic battery, did not prove that they 

 were united with the basis of these substances in such propor- 

 tions as to form water, nor indeed does he appear to have 

 entertained such an opinion himself. His opinion of the na- 



* The high conducting power of mercury for electricity renders it al- 

 most impossible to determine, by this method, whether metals in the fluid 

 state obey the same laws of conduction as when in the solid state. If they 

 do not, it is highly probable there is a general law, that all solids conduct 

 along their surface, and all fluids through their substance. The investigation 

 of such general law I propose to continue in another paper. 



