It is a color-annotated version of the 1824 <a href="https://en.wikipedia.org/wiki/Carnot_engine" class="extiw" title="en:Carnot engine">Carnot engine</a> diagram
<a href="https://en.wikipedia.org/wiki/User:Libb_Thims" class="extiw" title="en:User:Libb Thims">Libb Thims</a> (<a href="https://en.wikipedia.org/wiki/User_talk:Libb_Thims" class="extiw" title="en:User talk:Libb Thims">talk</a>)
circa 2008 <div style="display: none;">date QS:P,+2008-00-00T00:00:00Z/9,P1480,Q5727902</div>
<span class="int-own-work" lang="en">Own work</span> (<span lang="en" dir="ltr">Original text: <i><bdi lang="">I (<a href="https://en.wikipedia.org/wiki/User:Libb_Thims" class="extiw" title="en:User:Libb Thims">Libb Thims</a> (<a href="https://en.wikipedia.org/wiki/User_talk:Libb_Thims" class="extiw" title="en:User talk:Libb Thims">talk</a>)) created this work entirely by myself.</bdi></i></span>)