“Science Of Energetics. Although the mechanical hypothesis just mentioned may be useful and interesting as a means of anticipating laws, and connecting the science of thermodynamics with that of ordinary mechanics, still it is to be remembered that the science of thermodynamics is by no means dependent for its certainty on that or any other hypothesis, having been now reduced, to a system of principles, or general facts, expressing strictly the results of experiment as to the relations between heat and motive power. In this point of view the laws of thermodynamics may be regarded as particular cases of more general laws, applicable to all such states of matter as constitute Energy, or the capacity to perform work, which more general laws form the basis of the science of energetics, — a science comprehending, as special branches, the theories of motion, heat, light, electricity, and all other physical phenomena.”

The whole of this part of the subject depends on the consideration of the Intrinsic Energy of a system of bodies, as depending on the temperature and physical state, as well as the form, motion, and relative position of these bodies. Of this energy, however, only a part is available for the purpose of producing mechanical work, and though the energy itself is indestructible, the available part is liable to diminution by the action of certain natural processes, such as conduction and radiation of heat, friction, and viscosity. These processes, by which energy is rendered unavailable as a source of work, are classed together under the name of the Dissipation of Energy.
Theory of Heat http://books.google.com/books?id=DqAAAAAAMAAJ "Preface" (1871)

From the preface to Elementary Principles in Statististical Mechanics (1902), p. viii. Full book https://archive.org/details/elementaryprinc00gibbgoog

Source: Time, Structure and Fluctuations (1977), p. 1; Introduction.

A Text-Book of Thermodynamics with Special Reference to Chemistry (1913)

Introduction
Higher Mathematics for Chemical Students (1911)

Presidential Address at the British Association, "Biogenesis and abiogenesis" (1870) http://aleph0.clarku.edu/huxley/CE8/B-Ab.html; later published in Collected Essays, Vol. 8, p. 229
1870s

The Design of Experiments, Edinburgh: Oliver and Boyd, 1935, p. 18
1930s

Source: A Manual of the Steam Engine and Other Prime Movers (1859), p. 31
Context: Hypothesis Of Molecular Vortices. In thermodynamics as well as in other branches of molecular physics, the laws of phenomena have to a certain extent been anticipated, and their investigation facilitated, by the aid of hypotheses as to occult molecular structures and motions with which such phenomena are assumed to be connected. The hypothesis which has answered that purpose in the case of thermodynamics, is called that of "molecular vortices," or otherwise, the "centrifugal theory of elasticity. (On this subject, see the Edinburgh Philosophical Journal, 1849; Edinburgh Transactions, vol. xx.; and Philosophical Magazine, passim, especially for December, 1851, and November and December, 1855.)

The Notebooks of Leonardo da Vinci (1883), I Prolegomena and General Introduction to the Book on Painting