The law of the Conservation of Energy is already known — viz., that the sum of all the energies of the universe, actual and potential, is unchangeable.

A hypothetical theory is necessary, as a preliminary step, to reduce the expression of the phenomena to simplicity and order before it is possible to make any progress in framing an abstractive theory.

Discrepancy between theory and practice, which in sound physical and mechanical science is a delusion, has a real existence in the minds of men and that fallacy, through rejected by their judgments, continues to exert and influence over their acts.

This law (regarding the theoretical efficiency of heat engines by Mr. Joule), and the law of the maximum efficiency of heat engines, are particular cases of a general law which regulates all transformation of energy, and is the basis of the Science of Energetics.