The Machinery of the Universe: Mechanical Conceptions of Physical Phenomena

by A. E. Dolbear

in each case were properly mechanical ones part (but not all) of the time; for when the immaterial substances were dissociated from matter, where they had manifested themselves, no one concerned himself to inquire as to their whereabouts. They were simply off duty, but could be summoned, like the genii in the story of Aladdin's Lamp. Now, a mechanical conception of any phenomenon, or a mechanical explanation of any kind of action, must be mechanical all the time, in the antecedents as well as the consequents. Nothing else will do except a miracle.

During the fifty years, from about 1820 to 1870, a somewhat different kind of explanation of physical events grew up. The interest that was aroused by the discoveries in all the fields of physical science—in heat, electricity, magnetism and chemistry—by Faraday, Joule, Helmholtz, and others, compelled a change of conceptions; for it was noticed that each special kind of phenomenon was preceded by some other definite and known kind; as, for instance, that chemical action preceded electrical currents, that mechanical or electrical activity resulted from changing magnetism, and so on. As each kind of action was believed to be due to a special force, there were invented such terms as mechanical force, electrical force, magnetic, chemical and vital forces, and these were discovered to be

convertible into one another, and the “doctrine of the correlation of the physical forces” became a common expression in philosophies of all sorts. By “convertible into one another,” was meant, that whenever any given force appeared, it was at the expense of some other force; thus, in a battery chemical force was changed into electrical force; in a magnet, electrical force was changed into magnetic force, and so on. The idea here was the transformation of forces, and forces were not so clearly defined that one could have a mechanical idea of just what had happened. That part of the philosophy was no clearer than that of the imponderables, which had largely dropped out of mind. The terminology represented an advance in knowledge, but was lacking in lucidity, for no one knew what a force of any kind was.

The first to discover this and to repudiate the prevailing terminology were the physiologists, who early announced their disbelief in a vital force, and their belief that all physiological activities were of purely physical and chemical origin, and that there was no need to assume any such thing as a vital force. Then came the discovery that chemical force, or affinity, had only an adventitious existence, and that, at absolute zero, there was no such activity. The discovery of, or rather the appreciation of, what is implied by the term absolute zero, and

especially of the nature of heat itself, as expressed in the statement that heat is a mode of motion, dismissed another of the so-called forces as being a metaphysical agency having no real existence, though standing for phenomena needing further attention and explanation; and by explanation is meant the presentation of the mechanical antecedents for a phenomenon, in so complete a way that no supplementary or unknown factors are necessary. The train moves because the engine pulls it; the engine pulls because the steam pushes it. There is no more necessity for assuming a steam force between the steam and the engine, than for assuming an engine force between the engine and the train. All the processes are mechanical, and have to do only with ordinary matter and its conditions, from the coal-pile to the moving freight, though there are many transformations of the forms of motion and of energy between the two extremes.

During the past thirty years there has come into common use another term, unknown in any technical sense before that time, namely, energy. What was once called the conservation of force is now called the conservation of energy, and we now often hear of forms of energy. Thus, heat is said to be a form of energy, and the forms of energy are convertible into one another, as the so-called forces were formerly supposed to be transformable into one another.

We are asked to consider gravitative energy, heat energy, mechanical energy, chemical energy, and electrical energy. When we inquire what is meant by energy, we are informed that it means ability to do work, and that work is measurable as a pressure into a distance, and is specified as foot-pounds. A mass of matter moves because energy has been spent upon it, and has acquired energy equal to the work done on it, and this is believed to hold true, no matter what the kind of energy was that moved it. If a body moves, it moves because another body has exerted pressure upon it, and its energy is called kinetic energy; but a body may be subject to pressure and not move appreciably, and then the body is said to possess potential energy. Thus, a bent spring and a raised weight are said to possess potential energy. In either case, an energized body receives its energy by pressure, and has ability to produce pressure on another body. Whether or not it does work on another body depends on the rigidity of the body it acts upon. In any case, it is simply a mechanical action—body A pushes upon body B (Fig. 1). There is no need to assume anything more mysterious than mechanical action. Whether body B moves this way or that depends upon the direction of the push, the point of its application. Whether the body be a mass as large as the earth or as small as a molecule, makes no difference in

that particular. Suppose, then, that a (Fig. 2) spends its energy on b, b on c, c on d, and so on. The energy of a gives translatory motion to b, b sets c vibrating, and c makes d spin on some axis. Each of these has had energy spent on it, and each has some form of energy different from the other, but no new factor has been introduced between a and d, and the only factor that has gone from a to d has been motion—motion that has had its direction and quality changed, but not its nature. If we agree that energy is neither created nor annihilated, by any physical process, and if we assume that a gave to b all its energy, that is, all its motion; that b likewise gave its all to c, and so on; then the succession of phenomena

from a to d has been simply the transference of a definite amount of motion, and therefore of energy, from the one to the other; for motion has been the only variable factor. If, furthermore, we should agree to call the translatory motion α, the vibratory motion β, the rotary γ, then we should have had a conversion of α into β, of β into γ. If we should consider the amount of transfer motion instead of the kind of motion, we should have to say that the α energy had been transformed into β and the β into γ.