Ennis on the Origin of the Stars. “The Origin of the Stars, and the Causes of their Motions and their Light. By Jacob Ennis.” New York: D. Appleton &Co. 1867. 12mo, pp. 385. ³¹, [From The Nation 4.90 (21 March 1867): 231-232.] ³²

The author of this book has undertaken to explain the origin of the motions of the universe without having qualified himself for so great a task by so much as even making himself acquainted with one of' the simplest and most elementary of the laws of motion. He may have read in the course of his somewhat extensive researches that “action and reaction are equal” in all the known causes of changes in motion; but he has signally failed to understand what this law of motion truly signifies. And of the more recondite mathematical deductions from this and the two other laws of motion he appears to be quite unconscious.

That the mutual actions by attraction, repulsion, collision, and friction between the parts of a body or a system of bodies cannot change the motion of the centre of gravity of the body or system, or change the average movements of revolution about this centre as measured by the description of areas; or, to take concrete examples—the facts that a body cannot be raised from the earth by any terrestrial force without a depression of the earth by the same amount; that a body cannot be moved along the surface of the earth or around its centre of gravity without pushing the earth backwards by the same amount; that a railway train, whether moved by traction or by its own weight on a downward grade, cannot bring its freight to its destination without also turning the earth backwards by as many tons per mile; that a bird rises on the air only by forcing downward the air and the earth, and can only move forward by forcing the air backward by as many ounces per foot; that a sparrow cannot fall to the ground without raising the earth by an equal amount—these facts are elementary examples of laws of motion which, though we cannot presume the general reader to be familiar with them, ought to be known to any one who should undertake to discuss the mechanical problems of the “nebular hypothesis.” Yet the author of this book has attempted, in utter defiance of the laws of the “conservation of areas,” to account for the origin of the movements of revolution in the

solar system and in sidereal systems as results of the mutual gravitation of the parts of the nebulous masses, which he does not hesitate to believe were the primitive forms of these systems. And he has done this not only in defiance of the elementary principles of motion, but also against the authority of all the best writers on the subject with whose judgments on this question he is acquainted. He appears to regard these judgments as mere opinions, or as confessions on the part of the writers of their own inability to account on the nebular hypothesis for the origination of these movements; and ho therefore proposes by his contributions to remedy what he justly regards as a great deficiency in the hypothesis. But unluckily, instead of accomplishing what previous writers have failed to do, he has failed to see what previous writers have really accomplished, namely, the demonstration that the movements of revolution in the solar system could not have originated, as the author believes, in the interactions of the parts of the system, whatever may have been the original form of the system, and whatever the nature of forces of interaction, provided these have obeyed from the beginning the universal laws of motion.

Nothing further, therefore, requires to bo said about this part of our author’s treatise. But this is not the only thesis on which he has opposed himself to the world of living scientific authority as well as to scientific demonstrations. He proposes to go backward and revive the antiquated doctrine that chemical action is the cause of the light and heat of the sun and the stars; and to this doctrine, and its various relations, he devotes the greater part of his volume.

As in his other doctrine he attempts to do away with an insurmountable defect in the nebular hypothesis, so here he proposes a theory in opposition to its only demonstrated sufficiency. Though gravity cannot account for the motions of revolution in a system of bodies, it is able to account for the light and heat of the heavier masses like the sun, and this by the strictest of physical demonstrations, in which nothing is hypothetical except what the author regards as established—the nebular genesis of the sun and the stars. Once grant the author's premise, the nebular hypothesis, and by the strictest reasonings on mechanical principles, as extended by recent researches in physics, it is shown that the falling forces of the matter of the contracting sun are sufficient, or at least vastly more competent than any known chemical action, to account for its light and heat. As he reasons in one of his theories in contravention of the principle of the “conservation of areas,” so in the other he is at issue with the principle of the “conservation of power,” a principle which, though not so universal in its applications to the phenomena of visible motion as the former, has become, by the extension given it in the modern “mechanical theory of heat,” of equal validity and extent.

Of this principle the author has at least learned the name, though it is evident he does not understand it. By a confusion of the two things expressed by the word force, namely, a tendency to produce or arrest motion, and the special conditions, including the tendency, by which the production or arrest of motion is rendered possible, our author has arrived at the conclusion, in opposition to the “law of power,” that “force may be annihilated.” The force of gravity is nullified, he thinks, when a body rests on the ground and is prevented by the earth's surface from falling further. But in this confusion our author does not stand alone. Several eminent physicists have failed to comprehend, on account of this ambiguity in the word force, the application of the “law of power” to the phenomena of gravity. The law that no “power” can be extinguished except by being replaced by an equivalent “power,” whether in the form of a motion or as a special new condition for the production of an equivalent motion, does not apply, it is true, to gravity as mere weight in a body and irrespective of the body’s position. The position of the body, its height above the earth’s surface, is a factor in the measure of the “force” of gravity, as the word is used in this law. In view of this ambiguity Dr. Mayer has proposed to limit the use of the word “force,” and to define gravity or the simple weight of bodies not as a “force” but as a “property” of matter; and he proposes the name “falling force” for the “forces” into which gravity enters as a factor, as in the “force” exhibited by a body when placed unsupported at a height above the ground. Not only the weight but the height of the body enters into the conception of “force” thus limited and defined. But, in spite of Dr. Mayer’s clear exposition of this principle, our author has totally misconceived him. He says: “Mayer regards gravity as a property of matter, and not as one of the forces capable of conversion and reconversion.” In fact, Mayer proposes “falling force” as the name of the conditions for the production of motion into which gravity enters as a factor, and he does this simply to avoid an ambiguity of language, and not on account of any difficulty in the theory.

But the author says “the theory of the conservation of force is yet in its infancy.” He cannot, then, be aware that, so far as the relations of “falling forces” to the “living forces” of motion are concerned, the doctrine is almost as old as the theory of gravity; or that, by the recent extension of the doctrine to the force of heat, it is made equally extensive in all astronomical problems with the principles of the “conservation of the centre of gravity” and the “conservation of areas,” and is thus sufficiently mature to have inherited the problems which the author proposes to solve without its aid and in defiance of it. It is at least sufficiently mature in the minds of the most eminent modern physicists to discredit the “chemical theory,” which, in his ignorance of the doctrine, the author has attempted to revive.