midfeather

Century Dictionary and Cyclopedia

1. n. A hollow horizontal septum in the furnace of a steam-boiler, which, being filled with water, forms a sort of water-bridge, under and over which the flame of the fuel is caused to pass. The midfeather thus adds a very effective heating surface, while retaining the incandescent gases and rendering their combustion more complete before they pass into the cooler fiues or tubes of the boiler.

Wiktionary

1. n. A vertical water space in a firebox or combustion chamber within a steam boiler.
2. n. mining A support for the centre of a tunnel.

GNU Webster's 1913

1. n. (Steam Boilers) A vertical water space in a fire box or combustion chamber.
2. n. (Mining) A support for the center of a tunnel.