CHAPTER IV.
THE VARIOUS STATES OF MATTER Sec.1.THE STATICS OF FLUIDS The division of bodies into gaseous, liquid, and solid, and the distinction established for the same substance between the three states, retain a great importance for the applications and usages of daily life, but have long since lost their absolute value from the scientific point of view.
So far as concerns the liquid and gaseous states particularly, the already antiquated researches of Andrews confirmed the ideas of Cagniard de la Tour and established the continuity of the two states.
A group of physical studies has thus been constituted on what may be called the statics of fluids, in which we examine the relations existing between the pressure, the volume, and the temperature of bodies, and in which are comprised, under the term fluid, gases as well as liquids.
These researches deserve attention by their interest and the generality of the results to which they have led.

They also give a remarkable example of the happy effects which may be obtained by the combined employment of the various methods of investigation used in exploring the domain of nature.

Thermodynamics has, in fact, allowed us to obtain numerical relations between the various coefficients, and atomic hypotheses have led to the establishment of one capital relation, the characteristic equation of fluids; while, on the other hand, experiment in which the progress made in the art of measurement has been utilized, has furnished the most valuable information on all the laws of compressibility and dilatation.
The classical work of Andrews was not very wide.

Andrews did not go much beyond pressures close to the normal and ordinary temperatures.
Of late years several very interesting and peculiar cases have been examined by MM.

Cailletet, Mathias, Batelli, Leduc, P.Chappuis, and other physicists.