资料来源 : Webster's Revised Unabridged Dictionary (1913)

Motion \Mo"tion\, n. [F., fr. L. motio, fr. movere, motum, to
   move. See {Move}.]
   1. The act, process, or state of changing place or position;
      movement; the passing of a body from one place or position
      to another, whether voluntary or involuntary; -- opposed
      to {rest}.

            Speaking or mute, all comeliness and grace attends
            thee, and each word, each motion, forms. --Milton.

   2. Power of, or capacity for, motion.

            Devoid of sense and motion.           --Milton.

   3. Direction of movement; course; tendency; as, the motion of
      the planets is from west to east.

            In our proper motion we ascend.       --Milton.

   4. Change in the relative position of the parts of anything;
      action of a machine with respect to the relative movement
      of its parts.

            This is the great wheel to which the clock owes its
            motion.                               --Dr. H. More.

   5. Movement of the mind, desires, or passions; mental act, or
      impulse to any action; internal activity.

            Let a good man obey every good motion rising in his
            heart, knowing that every such motion proceeds from
            God.                                  --South.

   6. A proposal or suggestion looking to action or progress;
      esp., a formal proposal made in a deliberative assembly;
      as, a motion to adjourn.

            Yes, I agree, and thank you for your motion. --Shak.

   7. (Law) An application made to a court or judge orally in
      open court. Its object is to obtain an order or rule
      directing some act to be done in favor of the applicant.
      --Mozley & W.

   8. (Mus.) Change of pitch in successive sounds, whether in
      the same part or in groups of parts.

            The independent motions of different parts sounding
            together constitute counterpoint.     --Grove.

   Note: Conjunct motion is that by single degrees of the scale.
         Contrary motion is that when parts move in opposite
         directions. Disjunct motion is motion by skips. Oblique
         motion is that when one part is stationary while
         another moves. Similar or direct motion is that when
         parts move in the same direction.

   9. A puppet show or puppet. [Obs.]

            What motion's this? the model of Nineveh? --Beau. &
                                                  Fl.

   Note: Motion, in mechanics, may be simple or compound.

   {Simple motions} are: ({a}) straight translation, which, if
      of indefinite duration, must be reciprocating. ({b})
      Simple rotation, which may be either continuous or
      reciprocating, and when reciprocating is called
      oscillating. ({c}) Helical, which, if of indefinite
      duration, must be reciprocating.

   {Compound motion} consists of combinations of any of the
      simple motions.

   {Center of motion}, {Harmonic motion}, etc. See under
      {Center}, {Harmonic}, etc.

   {Motion block} (Steam Engine), a crosshead.

   {Perpetual motion} (Mech.), an incessant motion conceived to
      be attainable by a machine supplying its own motive forces
      independently of any action from without.

Center \Cen"ter\, n. [F. centre, fr. L. centrum, fr. round which
   a circle is described, fr. ? to prick, goad.]
   1. A point equally distant from the extremities of a line,
      figure, or body, or from all parts of the circumference of
      a circle; the middle point or place.

   2. The middle or central portion of anything.

   3. A principal or important point of concentration; the
      nucleus around which things are gathered or to which they
      tend; an object of attention, action, or force; as, a
      center of attaction.

   4. The earth. [Obs.] --Shak.

   5. Those members of a legislative assembly (as in France) who
      support the existing government. They sit in the middle of
      the legislative chamber, opposite the presiding officer,
      between the conservatives or monarchists, who sit on the
      right of the speaker, and the radicals or advanced
      republicans who occupy the seats on his left, See {Right},
      and {Left}.

   6. (Arch.) A temporary structure upon which the materials of
      a vault or arch are supported in position until the work
      becomes self-supporting.

   7. (Mech.)
      (a) One of the two conical steel pins, in a lathe, etc.,
          upon which the work is held, and about which it
          revolves.
      (b) A conical recess, or indentation, in the end of a
          shaft or other work, to receive the point of a center,
          on which the work can turn, as in a lathe.

   Note: In a lathe the

   {live center} is in the spindle of the head stock; the

   {dead center} is on the tail stock.

   {Planer centers} are stocks carrying centers, when the object
      to be planed must be turned on its axis.

   {Center of an army}, the body or troops occupying the place
      in the line between the wings.

   {Center of a} {curve or surface} (Geom.)
      (a) A point such that every line drawn through the point
          and terminated by the curve or surface is bisected at
          the point.
      (b) The fixed point of reference in polar co["o]rdinates.
          See {Co["o]rdinates}.

   {Center of curvature of a curve} (Geom.), the center of that
      circle which has at any given point of the curve closer
      contact with the curve than has any other circle whatever.
      See {Circle}.

   {Center of a fleet}, the division or column between the van
      and rear, or between the weather division and the lee.

   {Center of gravity} (Mech.), that point of a body about which
      all its parts can be balanced, or which being supported,
      the whole body will remain at rest, though acted upon by
      gravity.

   {Center of gyration} (Mech.), that point in a rotating body
      at which the whole mass might be concentrated
      (theoretically) without altering the resistance of the
      intertia of the body to angular acceleration or
      retardation.

   {Center of inertia} (Mech.), the center of gravity of a body
      or system of bodies.

   {Center of motion}, the point which remains at rest, while
      all the other parts of a body move round it.

   {Center of oscillation}, the point at which, if the whole
      matter of a suspended body were collected, the time of
      oscillation would be the same as it is in the actual form
      and state of the body.

   {Center of percussion}, that point in a body moving about a
      fixed axis at which it may strike an obstacle without
      communicating a shock to the axis.

   {Center of pressure} (Hydros.), that point in a surface
      pressed by a fluid, at which, if a force equal to the
      whole pressure and in the same line be applied in a
      contrary direction, it will balance or counteract the
      whole pressure of the fluid.