Pallet—Has different meanings, even among watchmakers. Generally, the part through which the escape wheel gives impulse to the balance or pendulum.
Pallet Staff—The arbor on which the pallet is mounted, and on which it turns.
Pallet Stone—The jewel on the contact face of the pallet, where it is struck by the teeth of the escape wheel.
Parallax—The apparent angular displacement of a heavenly body due to a change of the observer's position.
Pedometer—An instrument which registers the number of paces walked—hence if properly adjusted to the length of step of the wearer it gives the distance traversed.
Pendant—The small neck and knob of metal connecting the bow of a watch case with the band of the case.
Pendulum—A body suspended by a rod or cord and free to swing to and fro; used in clocks to regulate the velocity with which the driving power moves the wheels and hence the hands. The isochronism of a pendulum vibrating in a cycloidal arc was first discovered by Galileo but he did not apply it to clocks. Most authorities credit Christian Huyghens with that adaptation to instruments for keeping time. The pendulum was first suspended by a silk cord and thus vibrated in a circular instead of cycloidal arc. "Huyghens' Checks" were an unsuccessful attempt to remedy this. Dr. Hooke succeeded in remedying it by suspending the pendulum by a flat ribbon of spring steel.
Pendulum, Gridiron—Invented by Harrison in 1726, and still with slight improvements an effective timekeeper. The rod of this pendulum is constructed of five steel and four brass rods so arranged that those which expand most are counteracted by those of less expansion, and the length of the pendulum remains constant.