line of shadows

from The Collaborative International Dictionary of English v.0.48

Quadrat \Quad"rat\, n. [F. quadrat, cadrat. See {Quadrate}.]
   1. (Print.) A block of type metal lower than the letters, --
      used in spacing and in blank lines. [Abbrev. quad.]
      [1913 Webster]

   2. An old instrument used for taking altitudes; -- called
      also {geometrical square}, and {line of shadows}.
      [1913 Webster]