lls_.--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.

GENERAL OBSERVATIONS ON THE PROPERTIES OF CELLS.

From the number of different properties possessed by my cells, it might
be anticipated that the different combinations of those properties would
result in cells having every variety of action. This is found to be the
case. As a general rule, the cells are noteworthy in one respect only.
Thus, if a cell is extremely sensitive to light, it may not be specially
remarkable in other respects. As a matter of fact, however, the cells
most sensitive to the light are also "U B cells."

The property of sensitiveness to light is independent of the power to
generate current by exposure to light--the best current-generating cells
being only very moderately sensitive to light, and some of the most
sensitive cells generate scarcely any current at all. Current-generating
cells are, almost without exception, "U B cells;" and the best
current-generating cells are strongly polarized, showing a considerable
change of resistance by reversing the direction of a current through
them; and they are also strong "anode cells," i.e., the surface next to
the gold offers a higher resistance to a battery current than the other
surface of the selenium does. The power to generate a current is
temporarily weakened by sending