  The first part of this paper is a condensed synthesis of the matter presented
in several previous ones. It begins with an argumentation showing that the
first and second laws of thermodynamics are incompatible with one another if
they are not connected to relativity. The solution proposed consists of
inserting the Einstein mass-energy relation into a general equation that
associates both laws.
  The second part deals with some consequences of this new insight and its
possible link with gravitation. Despite a slight modification of the usual
reasoning, the suggested hypothesis leads to a simplification and extension of
the thermodynamic theory and to the idea that relativity is omnipresent around
us.
