Can someone explain this engine to me?

[ageattack]

Here are the links
http://books.google.ca/books?id=RN4...ss,+but+Spirit&redir_esc=y#v=onepage&q&f=true

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880002196_1988002196.pdf

I have read both but I don't understand how the gas circulates. The first link is probably the most helpful. Thanks.

 

[AlephZero]

http://en.wikipedia.org/wiki/Stirling_engine has some good diagrams of how two common types of Stirling engine work.