equal decrement of life

Decrement \Dec"re*ment\, n. [L. decrementum, fr. decrescere. See
   {Decrease}.]
   1. The state of becoming gradually less; decrease;
      diminution; waste; loss.
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            Twit me with the decrements of my pendants. --Ford.
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            Rocks, mountains, and the other elevations of the
            earth suffer a continual decrement.   --Woodward.
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   2. The quantity lost by gradual diminution or waste; --
      opposed to {increment}.
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   3. (Crystallog.) A name given by Ha["u]y to the successive
      diminution of the layers of molecules, applied to the
      faces of the primitive form, by which he supposed the
      secondary forms to be produced.
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   4. (Math.) The quantity by which a variable is diminished.
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   {Equal decrement of life}.
      (a) The decrease of life in a group of persons in which
          the assumed law of mortality is such that of a given
          large number of persons, all being now of the same
          age, an equal number shall die each consecutive year.
      (b) The decrease of life in a group of persons in which
          the assumed law of mortality is such that the ratio of
          those dying in a year to those living through the year
          is constant, being independent of the age of the
          persons.
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