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 cells.—­When a current of electricity flowing through one of my selenium cells is rapidly interrupted, a sound is given out by the cell, and that sound is the tone having the same number of air vibrations per second as the number of interruptions in the current.  The strength of the sound appears to be independent of the direction of the current through the cell.  It is produced on the face of the cell, no sound being audible from the back of the cell.  An alternating current also produces a sound corresponding to the number of changes of direction.  Experiments also show that, if a telephonically undulating current is passed through the cell, it will give out the speech or other sound corresponding to the undulations of the current—­and, furthermore, that the cell will sing or speak in like manner, without the use of a current, if a suitably varied light is thrown upon it while in closed circuit.