What is "variable exhaust"

Variable \Va"ri*a*ble\, a. [L. variabilis: cf. F. variable.]

1. Having the capacity of varying or changing; capable of alternation in any manner; changeable; as, variable winds or seasons; a variable quantity.

2. Liable to vary; too susceptible of change; mutable; fickle; unsteady; inconstant; as, the affections of men are variable; passions are variable.

   Lest that thy love prove likewise variable.
   --Shak.

   His heart, I know, how variable and vain!
   --Milton.

   Variable exhaust (Steam Eng.), a blast pipe with an adjustable opening.

   Variable quantity (Math.), a variable.

   Variable stars (Astron.), fixed stars which vary in their brightness, usually in more or less uniform periods.

   Syn: Changeable; mutable; fickle; wavering; unsteady; versatile; inconstant.