SENSITIVENESS TO CHANGE OF BATTERY POWER.
-----------------------+------------+------------+-------------
| Resistance | Resistance |
No. of cell. | with 25 | with 5 | Ratio of
| elements. | elements. | Change.
-----------------------+------------+------------+-------------
| ohms. | ohms. |
3/8 inch square, No. 1 | 40,000 | 30 | 1,333 to 1
3/8 " " " 2 | 13,000 | 40 | 325 "
1/4 " " " 1 | 1,400,000 | 123[8] | 11,381 "
1/2 " " " 2 | 500,000 | 62 | 8,064 "
1/2 " " " 5 | 3,500 | 21 | 167 "
Full size, No. 81 | 68,000 | 121 | 561 "
" " " 82 | 9,000 | 64 | 140 "
" " " 83 | 17,300 | 74 | 233 "
" " " 119 | 35,600 | 19 | 1,894 "
-----------------------+------------+------------+-------------
[Footnote 8: This measurement was obtained with 8 elements.]
The results in the table were obtained by changing the strength of
current by throwing in more or less of the battery. Like results can be
obtained by varying the current through the cell by any of the other
methods before specified. The above measurements were in dark.
5. _Dual state of selenium_.--My cells, when first made seem to have two
states or conditions. In one, their resistance is very low, in the other
it is high. When in the low state they are usually not very sensitive, in
any respect. I therefore raise the resistance, by sending an intermittent
or an alternating current though the cells, and in their new condition
they at once become extremely sensitive to light, currents, and other
influences. In some cases they drop to the low state again, and require
to be again brought up, until, after a number of such treatments, they
remain in the sensitive state. Occasionally a cell will persist in
remaining in the insensitive state. The before mentioned treatment raises
it up for a moment, but, before the bridge can be balanced and the
resistance measured, it again drops into the low or insensitive state.
Some cells have been thus stimulated into the high or sensitive state
repeatedly, and every means used to make them stay there, but without
avail; and they have had to be laid aside as intractable.
In the earlier stages of my investigations, before the discovery of this
dual state and the method of changing a cell from the insensitive to the
sensitive condition, hundreds of cells were made, finished, and tested,
only to be then ruthlessly destroyed and melted over, under the
impression that they were worthless. Now, I consider nothing worthless,
but expect sooner or later to make every cell useful for one purpose or
another.
The most singular part of this phenomenon is the wide difference in the
resistance of the cells in the two states. In the low state, it may be a
few ohms, or even a few hundredths of an ohm. In the high state, it is
the normal working resistance of the cell, usually between 5,000 and
200,000 ohms, but is often up among the millions. The spectacle of a
little selenium being stimulated, by a few interruptions of the current
through it, into changing its resistance from a fraction of an ohm up to
a million or several millions of ohms, and repeatedly and instantly
changing back and forth, up and down, through such a wide range, we might
almost say changing from zero to infinity, and the reverse, instantly, is
one which suggests some very far-reaching inquiries to the electrician
and the physicist. What is the nature of electrical conductivity or
resistance, and how is it so greatly and so suddenly changed?
6. _Radio-electric current generators_.--My cells can be so treated that
will generate a current by simple exposure to light or heat. The light,
for instance, passes through the gold and acts upon its junction with
the selenium, developing an electromotive force which results in a
current 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 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.
My experiments having been devoted especially to those branches of the
subject which promised to be more immediately practically valuable, I
have not pursued this inquiry very far, and offer it for your
consideration as being not only interesting, but possibly worthy of full
investigation.