What is "stationary air"

Stationary \Sta"tion*a*ry\ (-[asl]*r[y^]), a. [L. stationarius: cf. F. stationnaire. Cf. Stationer.]

1. Not moving; not appearing to move; stable; fixed.

   Charles Wesley, who is a more stationary man, does not believe the story.
   --Southey.

2. Not improving or getting worse; not growing wiser, greater, better, more excellent, or the contrary.

3. Appearing to be at rest, because moving in the line of vision; not progressive or retrograde, as a planet. Stationary air (Physiol.), the air which under ordinary circumstances does not leave the lungs in respiration. Stationary engine.

   1. A steam engine that is permanently placed, in distinction from a portable engine, locomotive, marine engine, etc. Specifically:

   2. A factory engine, in distinction from a blowing, pumping, or other kind of engine which is also permanently placed.

n. (context biology English) The air which under ordinary circumstances does not leave the lungs during respiration.