William John Macquorn Rankine

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.

William John Macquorn Rankine (5 July 1820 – 24 December 1872) was a Scottish engineer and physicist.

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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.

• 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.
  • "Outlines of the Science of Energetics". In Proceedings of the Philosophical Society of Glasgow, 1855. p.213.

• 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.
  • "Introductory Lecture on the Harmony of Theory and Practice in Mechanics". London : Richrad Griffin, 1856. p.4-5

• Another evil, and one of the worst which arises from the separation of theoretical and practical knowledge, is the fact that a large number of persons, possessed of an inventive turn of mind and of considerable skill in the manual operations of practical mechanics, are destitute of that knowledge of scientific principles which is requisite to prevent their being misled by their own ingenuity. Such men too often spend their money, waste their lives, and it may be lose their reason in the vain pursuits of visionary inventions, of which a moderate amount of theoretical knowledge would be sufficient to demonstrate the fallacy ; and for want of such knowledge, many a man who might have been a useful and happy member of society, becomes a being than whom it would be hard to find anything more miserable. The number of those unhappy persons — to judge from the patent-lists, and from some of the mechanical journals — must be much greater than is generally believed.
  • "On the harmony of theory and practice in mechanics" in The Mechanics' Magazine (1856). p.176

• 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.
  • Manual of Applied Mechanics, (1858) London and Glasgow : Richard Griffin and Company, p. 630

• It is possible to express the laws of thermodynamics in the form of independent principles, deduced by induction from the facts of observation and experiment, without reference to any hypothesis as to the occult molecular operations with which the sensible phenomena may be conceived to be connected; and that course will be followed in the body of the present treatise. But, in giving a brief historical sketch of the progress of thermodynamics, the progress of the hypothesis of thermic molecular motions cannot be wholly separated from that of the purely inductive theory.
  • A manual of the steam engine and other prime movers (1859), p. 27

• 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.)
  • A manual of the steam engine and other prime movers (1859), p. 31

• 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.
  • A manual of the steam engine and other prime movers (1859) p. 31

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• The hypothesis of molecular vortices is defined to be that which assumes that each atom of matter consists of a nuclens or central point enveloped by an elastic atmosphere, which is retained in its position by attractive forces, and that the elasticity due to heat arises from the centrifugal force of those atmospheres revolving or oscillating about their nuclei or central points. According to this hypothesis quantity of heat is the vis viraof the molecular revolutions or oscillations.

• Atoms of matter, of whatever kind, are constantly attracted straight towards each other by gravitating force; and atoms of different substances are in certain cases, if not in all cases, also attracted straight towards each other by the force of chemical affinity. Any atom is furthermore forcibly attracted towards a contiguous atom having more heat than itself; but this force of attraction ceases, and the two atoms are forcibly repelled straight from each other at the instant when an equilibrinm of temperature is established between them. In this way the communication of heat is attended by, although it is not cansed by, molecular motion. The motion attending the communication of heat may account for the phenomena of light. When heat is not in course of communication through a body its particles are at rest, at distances from each other at which the intermolecular forces are in equilibrio; heat acting in this case as a quiescent force, which may perhaps be understood by the term static tension. All other forces than that of heat are supposed to be inseparable from the same particles of matter, but the force of heat may in part permanently forsake one particle of matter for another, although no particle of matter can be ever forsaken wholly by heat. Substituting "fluid" for "force," this hypothesis of heat will strongly remind the reader of the Franklinian hypothesis of electricity, according to which the electric fluid is assumed to be ideo-repulsive or repelling its own particles, but attractive of all other matter.

• In any assemblage of atoms, the least active exertion of force must be attended with a progressive expenditure of heat, the particles nearest to the point of effort being first cooled, when an instant transmission of force would take place from those next to them, and so on throughout the heated mass as long as active force was exerted, or until the temperature of the whole had fallen to that of matter into which force or heat was escaping.