We can thus follow closely all questions concerning the displacements of the equilibrium, and find a relation of the first importance between the masses of the bodies which react in order to constitute a system in equilibrium.
The statics thus constructed constitutes at the present day an important edifice to be henceforth classed amongst historical monuments.

Some theorists even wish to go a step beyond.

They have attempted to begin by the same means a more complete study of those systems whose state changes from one moment to another.

This is, moreover, a study which is necessary to complete satisfactorily the study of equilibrium itself; for without it grave doubts would exist as to the conditions of stability, and it alone can give their true meaning to questions relating to displacements of equilibrium.
The problems with which we are thus confronted are singularly difficult.

M.Duhem has given us many excellent examples of the fecundity of the method; but if thermodynamic statics may be considered definitely founded, it cannot be said that the general dynamics of systems, considered as the study of thermal movements and variations, are yet as solidly established.
Sec.5.