3. The two surfaces of the selenium act differently toward currents sent into them from the contiguous conductors.  One surface offers a higher resistance to the current than the other.  The former I utilize as the anode surface, as I have found that the cell is more sensitive to light when the current enters at that surface, which is ordinarily the one covered by the gold or other transparent conductor.  Some cells have this property but feebly developed; but in one instance the resistance offered to the current by the anode surface was 256 times as high as that offered by the cathode surface to the same current.  In the majority of cases, however, the ratio does not exceed ten times.  Table B gives some recent results.

TABLE B.

SENSITIVENESS TO REVERSAL OF DIRECTION OF CURRENT.

-----------------------+--------------+----------------

--+---------
|              |   Resistance     |
No. of cell.       |   Battery.   | “gold  | “gold   | Ratio
|              | anode."|cathode."|
-----------------------+--------------+--------+---------+--

-------
|              |  ohms. |  ohms.  |
3/8 inch square.  No. 4 |  5 elements. | 20,000 |  1,000  | 20  to 1
"     "     "  3 |   Se. cell.  |  6,500 |    400  | 16.2 "
Full size, No. 13   |  1 element.  |  9,000 |    800  | 11.2 "
"    "    "  14   |  5    "      |  2,440 |    130  | 18   "
"    "    "  15   |  5    "      |  4,640 |    210  | 22   "
"    "    "  27   |  5    "      |  6,900 |    440  | 16   "
"    "    " 126   |  1    "      |  5,000 |    330  | 15   "
-----------------------+--------------+--------+---------+--

-------

The direction of the current is always indicated by stating the position of the gold electrode, by the terms “gold anode” and “gold cathode.”  The above measurements were made in dark.

4. Sensitiveness to change of battery power.—­My cells are extremely sensitive to any change in the strength or character of the current flowing through them, which is shown by a corresponding change in the resistance of the cell.  I can, therefore, vary the resistance of one of my cells in many ways, and the following may be specified—­

(a) By changing the potential or electromotive force of the current through the cell.

(b) By changing the “quantity” of the battery or current.

(c) By putting more or less resistance in the circuit.

(d) By dividing the current, by one or more branch circuits or shunts around the cell.

(e) By varying the resistance in any or all of said circuits.

A cell whose resistance becomes greater as the battery power becomes greater, and vice versa, I call an “L B cell” signifying Like the Battery power.  A “U B cell” is one whose resistance becomes greater as the battery power (or strength of current) becomes less, and vice versa, being Unlike the Battery power, or current strength.