The present invention relates to a method of converting thermal energy into mechanical energy using a non-gaseous working medium present in an apparatus comprising a plurality of heat exchangers and an outgoing shaft. In accordance with the invention, the apparatus used comprises a multitude of chamber units, a chamber unit comprising an inlet for introducing heat exchange medium and an outlet for discharging heat exchange medium as well as a closed chamber having a heat exchanger wall for exchanging heat between working medium inside the closed chamber and the heat exchange medium introduced into the chamber unit via said inlet for introducing heat exchange medium and heat exchange medium is passed around so as to do work when it is giving off heat to a chamber unit containing relatively cool working medium and recuperate heat when it is passed through a chamber unit containing relatively warm working medium. The invention also relates to an apparatus for performing the method.