The evolution of one force or mode of force into another has naturally induced many to regard all the different natural agencies as reducible to unity, and much ingenuity has been expended on the question which force is the efficient cause of all the others. One says electricity, another chemical action, another gravity. Professor Grove believes that all are wrong: each mode of force may produce the others, and none can be produced except by some other as an anterior force. We can no more determine which is the efficient cause than we can determine whether the chicken is the cause of the egg, or the egg the cause of the chicken. The tendency of recent researches however is toward the conclusion that all the physical forces are simply modes of motion; that as, in the case of friction, the gross or palpable motion which is arrested by the contact of another body, is subdivided into molecular motions or vibrations (or as Helmholtz expresses it, peculiar shivering motions of the ultimate particles of bodies), which motions are only heat or electricity, as the case may be; so the other affections are only matter moved or molecularly agitated in certain definite directions. The identity of motion with heat was established in the last century by our countryman, Count Rumford, and has lately been beautifully illustrated by Professor Tyndall in his charming lectures on "Heat considered as a Mode of Motion." Dr. Mayer, of Heilbronn, and Mr. Joule, of Manchester, independently of each other, established the exact ratio between heat and motive power, showing that a quantity of heat sufficient to raise one pound of water one degree Fahrenheit in temperature is able to raise to the height of one foot a weight of 772 pounds; and conversely, that a weight of 772 pounds falling from a height of one foot evolves enough heat to raise the temperature of a pound of water one degree. That is, this quantity of force, expressed as 772 "foot-pounds," is to be regarded as the mechanical equivalent of 1° of temperature. Professor Grove considers at some length the identity of motion with other forms of force, especially electricity and magnetism, and alludes briefly to the inevitable consequence of this theory, that the different forces must bear an exact quantitative relation to each other. "The great problem which remains to be solved," he says, "in regard to the correlation of physical forces, is this establishment of their equivalents of power, or their measurable relation to a given standard."
The doctrine of the conservation or persistence of force seems to flow naturally from what has been said above. It means simply that force is never destroyed: when it ceases to exist in one form it only passes into another. Power or energy, like matter, is neither created nor annihilated: "Though ever changing form, its total quantity in the universe remains constant and unalterable. Every manifestation of force must have come from a pre-existing equivalent force, and must give rise to a subsequent and equal amount of some other force. When, therefore, a force or effect appears, we are not at liberty to assume that it was self-originated, or [{427}] came from nothing; when it disappears we are forbidden to conclude that it is annihilated: we must search and find whence it came and whither it has gone; that is, what produced it, and what effect it has itself produced." (Introduction, p. xiii.) This branch of the subject will be found clearly and concisely treated in Professor Faraday's paper on "The Conservation of Force" (pp. 359-383).
Dr. Carpenter carries the new theory into the higher realms of nature, and shows the applicability of the principle of correlation and conservation to the vital phenomena of growth and development. "These forces," he says, "are generated in living bodies by the transformation of the light, heat, and chemical action supplied by the world around, and are given back to it again, either during their life, or after its cessation, chiefly in motion and heat, but also, to a less degree, in light and electricity." Vital force is that power by virtue of which a germ endowed with life is developed into an organization of a type resembling that of its parents, and which subsequently maintains that organism in its integrity. The prevalent opinion until lately has been that this force is inherent in the germ, which has been supposed to derive from its parent not merely its material substance, but a germ-force, in virtue of which it develops and maintains itself, beside imparting a fraction of the same force to each of its descendants. In this view of the question, the aggregate of all the germ-forces appertaining to the descendants, however numerous, of a common parentage, must have existed in the original progenitors. Take the case of the successive viviparous broods of Aphides, which (it has been calculated) would amount in the tenth brood to the bulk of five hundred millions of stout men: a germ-force capable of organizing this vast mass of living structure must have been shut up in the single individual, weighing perhaps the 1-1000th of a grain, from which the first brood was evolved! So, too, in Adam must have been concentrated the germ-force of every individual of the human race, from the creation to the end of the world. This, says Dr. Carpenter, is a complete reductio ad absurdum. According to his theory, the germ supplies not the force, but the directive agency. The vital force of an animal or a plant is supplied by the same physical agencies which we have considered above.
Dr. Youmans in his introduction is disposed to push this part of the subject yet further, and to identify physical with intellectual force; but into this dangerous region it is unnecessary to follow him.
Some of the explanations of natural phenomena which are drawn as corollaries from the new theory of forces are in the highest degree curious and beautiful. Many of our readers will find Dr. Mayer's paper "On Celestial Dynamics" one of the most interesting portions of the book. He applies the principle of the convertibility of heat and motion to the question of the origin of the sun's heat, which he ascribes to the fall of asteroids upon the sun's surface. That an immense number of cosmical bodies are moving through the heavens and streaming toward the solar surface, is well known to all physicists. Now it is calculated that a single asteroid falling into the sun generates from 4,600 to 9,200 times as much heat as would be generated by the combustion of an equal mass of coal, and the mass of matter which in the form of asteroids falls into the sun every minute is from two to four hundred thousand billions of pounds! The enormous heat which must be evolved by such a bombardment is almost inconceivable.
REAL AND IDEAL. By John W. Montclair. 12mo., pp. 119. Philadelphia: Frederick Leypoldt. New York: Hurd & Houghton.
This is a dainty little volume of poems, partly translated from the German, partly the offspring of the native muse. They are simple, unpretending, and as a general thing melodious. The author probably has not aspired to a very high place in the temple of fame; without the ambition to produce anything very striking or very original, he has been satisfied with the endeavor which he pithily expresses in his "Prologue:"
"Clearer to think what others thought before—
Keenly to feel th' afflictions of our race—
Better to say what others oft have said—"
and if he does not always think clearer and speak better than those in whose footsteps he treads, there is at all events that in his verse which promises better [{428}] things after more practice. His faults are chiefly those of carelessness and inexperience. His metaphors are superabundant, and sometimes incongruous. He has a good ear for rhythm; but we often find him tripping in his prosody. Often too the requirements of the metre lead him to eke out a line with expletives, or weaken it with unnecessary epithets.
But we can commend the book for its healthy tone. Mr. Montclair has no tendency toward the morbid psychological school of poetry. He delights rather in the contemplation of nature, and in moralizing on the life and aspirations of man. In neither does he discover much that is new; but the natural beauties which he sings are those of which we do not easily tire, and his moral reflections are just though they may not be profound. For the matter of his translations he has chosen some of the simplest and shortest of the German legendary ballads. Several of them are rendered with considerable neatness and delicacy. The following version of a ballad to which attention has been particularly called of late, is a favorable specimen of Mr. Montclair's powers: