a battery current through the cell while
exposed to light, in either direction. The current generated by exposure
to light is also weakened by warming the cell, unless the cell is
arranged for producing current by exposure to heat.

The properties of sensitiveness to light and to change of battery power
are independent of each other, as I have cells which are sensitive to
change of current but absolutely insensitive to light--their resistance
remaining exactly the same whether the cells are in darkness or in
sunlight. I also have cells which are sensitive to light, but are
unaffected by change of battery power, or by reversing the direction of
the current through them.

The sensitiveness to change of battery power is also independent of the
sensitiveness to reversal of direction of the current. Among the best "L
B cells," some are "anode cells" and others are "cathode cells," while
still others are absolutely insensitive to reversal of current or to the
action of light.

_Constancy of the resistance_.--A noticeable point in my cells is the
remarkable constancy of the resistance in sunlight. Allowing for
differences in the temperature, the currents, and the light, at different
times, the resistance of a cell in sunlight will remain practically
constant during months of use and experiments, although during that time
the treatments received may have varied the resistance in dark hundreds
of thousands of ohms--sometimes carrying it up, and at others carrying it
down again, perhaps scores of times, until it is "matured," or reaches
the condition in which its resistance becomes constant.

As has already been stated, the sensitiveness of a cell to light is
increased by proper usage. This increased sensitiveness is shown, not by
a lowered resistance in light, but by an increased resistance in dark.
This change in the cells goes on, more or less rapidly, according as it
is retarded or favored by the treatment it receives, until a maximum is
reached, after which the resistance remains practically constant in both
light and dark, and the cell is then "matured," or finished. The
resistance in dark may now be 50 or even 100 times as high as when the
cell was first made, yet, whenever exposed to sunlight it promptly shows
the same resistance that it did in the beginning. The various treatments,
and even accidents, through which it has passed in the mean time, seem
not to have stirred its molecular arrangement under the action of