o the car
circuit.

Potential Difference. Abbreviated P. D. Found on test curves.
Synonymous with voltage.

Rate. Number of amperes for charge or discharge. Also used to express
time for either.

Rectifier. Apparatus for converting alternating current into direct
current.

Resistance. Material (usually lamps or wire) of low conductivity
inserted in a circuit to retard the flow of current. By varying the
resistance, the amount of current can be regulated. Also the property
of an electrical circuit whereby the flow of current is impeded.
Resistance is measured in ohms. Analogous to the impediment offered by
wall of a pipe to flow of water therein.

Rheostat. An electrical appliance used to raise or lower the
resistance of a circuit and correspondingly to decrease or increase
the current flowing.

Rib. (See Bridge.)

Ribbed. (See Separator.)

Reversal. Reversal of polarity of cell or battery, due to excessive
discharge, or charging in the wrong direction.

Rubber Sheets. Thin, perforated hard rubber sheets used in combination
with the wood separators in some types of batteries. They are placed
between the grooved side of the wood separators and the positive plate.

Sealing. Making tight joints between jar and cover; usually with a
black, thick, acid-proof compound.

Sediment. Loosened or worn out particles of active material fallen to
the bottom of cells; frequently called "mud."

Sediment Space. That part of jar between bottom and top of bridge.

Separator. An insulator between plates of opposite polarity; usually
of wood, rubber or combination of both. Separators are generally
corrugated or ribbed to insure proper distance between plates and to
avoid too great displacement of electrolyte.

Short Circuit. A metallic connection between the positive and negative
plates within a cell. The plates may be in actual contact or material
may lodge and bridge across. If the separators are in good condition,
a short circuit is unlikely to occur.

Spacers. Wood strips used in some types to separate the cells in the
case, and divided to provide a space for the tie bolts.

Specific Gravity. The density of the electrolyte compared to water as
a standard. It indicates the strength and is measured by the
hydrometer.

Spray. Fine particles of electrolyte carried up from the surface by
gas bubbles. (See Gassing.)

Starting Rate. A specified current in amperes at which a discharged
battery may be charged at the begi