3. Conclusion

This first part, devoted to the action of pressure on matter, has shown that, until very recently, theorists had difficulty grasping the notion of a liquid medium. Although somewhat better described, the fluid state also presents areas where thermodynamics must appeal to notions of statistical physics (Wilson's exponent) that disturb the classical conception of the laws of thermodynamics. Despite this, the study of the action of pressure on liquids and gases was historically the first to be systematically undertaken, essentially for practical and industrial needs. Indeed, the development of pressure sensors, weather forecasting, the performance of submarines, certain reactions in heavy chemistry... require knowledge of the thermodynamic properties of fluids under pressure. From a research point of view, the development of diamond anvil cells and their popularization, over the last thirty...