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 rnetal, 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 v/ith 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 Jlidd 
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. 
