  The present work is a translation from french to english of our previous
\g{D\'emocrite et la puissance motrice du feu}, amended on a number of
respects. It is mainly of historical and pedagogical interest. We suggest that
the concepts introduced in the ancien Greece by Anaximander (flat earth) and
Democritus (corpuscles moving in vacuum) allow us to obtain through qualitative
observations and plausible generalizations the maximum efficiency and work of
heat engines, results that were firmly established around 1824 by Carnot. A
prologue introduces the subject. We next present the concept of thermal
equilibrium and consider a model consisting of two reservoirs located at
different altitudes, each with $g$ sites. Each site may contain a specified
number of corpuscles. One particular site plays the role of \g{working agent}.
We subsequently consider an alternative model consisting of independent
corpuscles submitted to gravity and in contact with heat baths. Only average
quantities are considered, leaving out fluctuations and questions of stability.
