ent proceeding from the metal back, through the external circuit, to
the gold in front, thus forming a photo-electric dry pile or battery. It
should preferably be protected from overheating, by an alum water cell or
other well known means.

The current thus produced is radiant energy converted into electrical
energy directly and without chemical action, and flowing in the same
direction as the original radiant energy, which thus continues its
course, but through a new conducting medium suited to its present form.
This current is continuous, constant, and of considerable electromotive
force. A number of cells can be arranged in multiple arc or in series,
like any other battery. The current appears instantly when the light is
thrown upon the cell, and ceases instantly when the light is shut off. If
the light is varied properly, by any suitable means, a telephonic or
other corresponding current is produced, which can be utilized by any
suitable apparatus, thus requiring no battery but the selenium cell
itself. The strength of the current varies with the amount of light on
the cell, and with the extent of the surface which is lighted.

I produce current not only by exposure to sunlight, but also to dim
diffused daylight, to moonlight, and even to lamplight. I use this
current for actual working purposes, among others, for measuring the
resistance of other selenium cells, with the usual Wheatstone's bridge
arrangement, and for telephonic and similar purposes. Its use for
photometric purposes and in current regulators will be mentioned further
on. It is undoubtedly available for all uses for which other battery
currents are employed, and I regard it as the most constant, convenient,
lasting, readily used, and easily managed pile or battery of which I have
any knowledge. On the commercial scale, it could be produced very
cheaply, and its use is attended by no expense, inasmuch as no liquids or
chemicals are used, the whole cell being of solid metal with a glass in
front, for protection against moisture and dust. It can be transported or
carried around as easily and safely as an electro-magnet, and as easily
connected in a circuit for use wherever required. The current, if not
wanted immediately, can either be "stored" where produced, in storage
batteries of improved construction devised by me, or transmitted over
suitable conductors to a distance, and there used, or stored as usual
till required.

7. _Singing and speaking ce