scientific work of the
laboratory. Now that electricity purifies copper as fire cannot, the
mathematician is able to treat his problems of long-distance
transmission, of traction, of machine design, with an economy and
certainty impossible when his materials were not simply impure, but
impure in varying and indefinite degrees. The factory and the workshop
originally took their magneto-machines from the experimental laboratory;
they have returned them remodelled beyond recognition as dynamos and
motors of almost ideal effectiveness.

A galvanometer actuated by a thermo-electric pile furnishes much the
most sensitive means of detecting changes of temperature; hence
electricity enables the physicist to study the phenomena of heat with
new ease and precision. It was thus that Professor Tyndall conducted
the classical researches set forth in his "Heat as a Mode of Motion,"
ascertaining the singular power to absorb terrestrial heat which makes
the aqueous vapours of the atmosphere act as an indispensable blanket to
the earth.

And how vastly has electricity, whether in the workshop or laboratory,
enlarged our conceptions of the forces that thrill space, of the
substances, seemingly so simple, that surround us--substances that
propound questions of structure and behaviour that silence the acutest
investigator. "You ask me," said a great physicist, "if I have a theory
of the _universe_? Why, I haven't even a theory of _magnetism_!"

The conventional phrase "conducting a current" is now understood to be
mere figure of speech; it is thought that a wire does little else than
give direction to electric energy. Pulsations of high tension have been
proved to be mainly superficial in their journeys, so that they are best
conveyed (or convoyed) by conductors of tubular form. And what is it
that moves when we speak of conduction? It seems to be now the molecule
of atomic chemistry, and anon the same ether that undulates with light
or radiant heat. Indeed, the conquest of electricity means so much
because it impresses the molecule and the ether into service as its
vehicles of communication. Instead of the old-time masses of metal, or
bands of leather, which moved stiffly through ranges comparatively
short, there is to-day employed a medium which may traverse 186,400
miles in a second, and with resistances most trivial in contrast with
those of mechanical friction.

And what is friction in the last analysis but the production of moti