The Collaborative International Dictionary of English v.0.48:

Bow-compass \Bow"-com`pass\, n.; pl. Bow-compasses.
   1. An arcograph.
      [1913 Webster]

   2. A small pair of compasses, one leg of which carries a
      pencil, or a pen, for drawing circles. Its legs are often
      connected by a bow-shaped spring, instead of by a joint.
      [1913 Webster]

   3. A pair of compasses, with a bow or arched plate riveted to
      one of the legs, and passing through the other.
      [1913 Webster]