It was first enunciated, like the last named, although prior to it in time, in consequence of considerations which deal only with heat and mechanical work.

Like it, too, it has evolved, grown, and invaded the entire domain of physics.

It may be interesting to examine rapidly the various phases of this evolution.

The origin of the principle of Carnot is clearly determined, and it is very rare to be able to go back thus certainly to the source of a discovery.

Sadi Carnot had, truth to say, no precursor.