Sir W.Ramsay and Mr S.Young have made known the isothermal diagrams[6] of a certain number of liquid bodies at the ordinary temperature.

They have thus been able, while keeping to somewhat restricted limits of temperature and pressure, to touch upon the most important questions, since they found themselves in the region of the saturation curve and of the critical point.
[Footnote 6: By isothermal diagram is meant the pattern or complex formed when the isothermal lines are arranged in curves of which the pressure is the ordinate and the volume the abscissa .-- ED.] But the most complete and systematic body of researches is due to M.
Amagat, who undertook the study of a certain number of bodies, some liquid and some gaseous, extending the scope of his experiments so as to embrace the different phases of the phenomena and to compare together, not only the results relating to the same bodies, but also those concerning different bodies which happen to be in the same conditions of temperature and pressure, but in very different conditions as regards their critical points.
From the experimental point of view, M.Amagat has been able, with extreme skill, to conquer the most serious difficulties.

He has managed to measure with precision pressures amounting to 3000 atmospheres, and also the very small volumes then occupied by the fluid mass under consideration.

This last measurement, which necessitates numerous corrections, is the most delicate part of the operation.

These researches have dealt with a certain number of different bodies.