lic connection being
established between the other end of the battery and the water-pipes
under the street. As long as the electric main continues unconnected
with the water-pipes, the circuit is incomplete and no current will
flow; but if any part of the main, however distant from the battery,
be connected with the adjacent water-pipes, the circuit will be
completed and the current will flow. Supposing our battery to be at
Charing Cross, and our rod of copper to be tapped opposite Somerset
House, a wire can be carried from the rod into the building, and the
current passing through the wire may be subdivided into any number of
subordinate branches, which reunite afterwards and return through the
water-pipes to the battery. The branch currents may be employed to
raise to vivid incandescence a refractory metal like iridium or one of
its alloys. Instead of being tapped at one point, our main may be
tapped at one hundred points. The current will divide in strict
accordance with law, its power to produce light being solely limited
by its strength. The process of division closely resembles the
circulation of the blood; the electric main carrying the outgoing
current representing a great artery, the water-pipes carrying the
return current representing a great vein, while the intermediate
branches represent the various vessels by which the blood is
distributed through the system. This, if I understand aright, is Mr.
Edison's proposed mode of illumination. The electric force is at
hand. Metals sufficiently refractory to bear being raised to vivid
incandescence are also at hand. The principles which regulate the
division of the current and the development of its light and heat are
perfectly well known. There is no room for a 'discovery,' in the
scientific sense of the term, but there is ample room for the exercise
of that mechanical ingenuity which has given us the sewing machine and
so many other useful inventions. Knowing something of the intricacy
of the practical problem, I should certainly prefer seeing it in Mr.
Edison's hands to having it in mine. [Footnote: More than thirty years
ago the radiation from incandescent platinum was admirably
investigated by Dr. Draper of New York.]

*****

It is sometimes stated as a recommendation to the electric light, that
it is light without heat; but to disprove this, it is only necessary
to point to the experiments of Davy, which show that the heat of the
voltaic arc tran