EVOLUTION OF POWER.
Animal organisms or mechanical contrivances which appear as the immediate sources of mechanical motion arc termed "prime movers," or, in mechanical nomenclature, " motors." A motor is, therefore, the prime means of mechanical motion, or, so to speak, the motive tool. Among animate organisms considered as motors or physico-dynamic machines are included a number of animals, both men and beasts, whose muscular power is extensively utilized as a prime mover, particularly in the less advanced stages of industrial development.
Mechanical contrivances as motors may be divided into the following classes: (r) Machines which utilize gravitation, including mainly water power motors, or hydro-dynamic machines; (2) wind-power motors, or aero-dynamic machines; and (3) heat-motors, or thermo-dynamic ma chines, including steam- and hot-air engines; percussion motors, or gaseo-dynamic machines; chemical motors, such as galvano-dynamic, ammonia-gas, and other similar engines.
According to modern views of physical science, the motors must be considered, primarily as simply the vehicles of force.
Force is that property of matter which manifests itself as causing or resisting motion, and in its primordial form is postulated as molecular motion, the latter being assumedly due to the reciprocal attraction of the ultimate atoms of matter.
Though modern research has increased the number of the natural ele ments from four, as held by the ancients, to about seventy, as now recog nized by chemistry, the tendency in other branches of the physical sciences has been the reverse. Thus the study of the subject has conclusively proved that the many elementary forces which were formerly supposed to "govern the world" must be considered simply as various manifestations of one elementary force, and the law which governs the change of one form of force to another has been termed the " law of the correlation of the physical forces." Every manifestation of force, whether in the form of mechanical motion, heat, light, electricity, magnetism, or chemical affinity, is now demonstrated to be but a specialized form of a single force; and this force, as already stated, is that of reciprocal attraction. It is this force which binds together the constituent parts of every object, holds terrestrial bodies to the earth, causes the planets to revolve around the sun, and impels the suns with their systems around in the spaces of the cosmos. Thus it is this prime force which constitutes the original motive power in all so-called " motors." That gravitation and elasticity are nothing but effects of attraction— the latter those of the attraction of the separate molecules of bodies, and the former those of the attraction of the sum of molecules composing them —needs no further explanation. But steam-power and the expansive
power of gases are in the first place the effects of heat, which in its turn is an effect of the reciprocal attraction of the atoms of matter or of the ether surrounding matter—in other words, of molecular motion. All other forms of force, such as light, electricity, etc., have been proved to be but varying conditions of this molecular motion, and thus it follows that all force, whether it be muscular power (independent of the idea of will or consciousness) or any other form of motive power, can be completely traced back to the prime element of atomic motion, or molecular attrac tion. However complicated the combination of proximate causes and effects, all can finally be deduced from the one cause named.
Thus water-power is the result of a series of changes, each change being the effect of a preceding cause, which in its turn is an effect of an antecedent cause, and so back to the original condition of force in the form of molecular motion. A certain quantity of water flowing downward from a height by reason of the attraction of the earth, produces a mechan ical effect corresponding to the height of fall; but when all has reached its level, no further effect is possible without a further change involving an expenditure of force to bring about the change. To continue the same mechanical effect as before, the water must again be raised to the height. This, in nature, is accomplished through the agency of the sun's heat act ing in conjunction with that of the earth, which produces evaporation into the atmosphere. The changes of day and night cause changes in tempera ture: when the latter lessens, the evaporated water condenses, is precipi tated from the clouds, falls to the earth by reason of the attraction of gravi tation, and, collecting at various levels, renews its downward flow and its mechanical effect; and thus the force of heat, obtained in this case, as we have noted, directly from the sun and from the earth, is translated into the mechanical effect of the descending water. In like manner all other mechanical effects can be traced through a variety of causes to the force of heat, which, as has been observed, is a state of atomic motion.
Nature furnishes us with ready motive power in the shape of moving air and water. All other forms of mechanical motion, not excepting mus cular power, require the application of heat, and this, practically in all cases, is obtained through combustion. In modern times heat motors have almost wholly superseded all others, and the department of thermo dynamic machines comprises, therefore, by far the most important class of motive tools.