2. All physical forces, such as hght, heat, chemical affinities, electricity, magnetism, etc., etc., are convertible. Light may be converted into hfeat, and heat into light ; either into electricity, and electricity into either ; and so through the whole range. This is what is called the correlation of forces. Count Rumford, in a com- munication to the Royal Society of London, in 1798, satisfied that the heat generated in boring cannon could not be otherwise ac- counted for, advanced the doctrine that heat is a peculiar mode of motion. Since then the doctrine has been generalized, and it is now the commonly received opinion that all the physical forces are resolvable into motion. This genei*alization, however, is not ac- cepted by all scientific men. They find it impossible to conceive how gravitation, which acts instantaneously at all distances, can be motion. It is simply a force which tends to produce motion.
3. This motion, however, is not of a fluid, or ether, or any other imponderable substance peculiar to each particular kind of force. As sound consists in, or rather, is produced by the vibrations of the atmosphere, it was natural to assume that light was the undu- lation of one medium, heat of another, electricity of another. This theory is discarded. The motion intended is motion in the molecules of the matter affected. When iron is heated, nothing is added to it. There is no imponderable substance called caloric. All that occurs is, that the molecules of the iron are agitated in a particular way. If the iron be magnetized, it is only a different kind of motion imparted to its constituent atoms. So of all other kinds of force. When, however, light or heat is radiated from a distant object, the motion which constitutes these forces must be transmitted through some medium. For where there is motion, there must be something that moves. And, therefore, if heat be motion in the molecules of the sun, that heat could not reach us unless there was some material medium between us and the sun.
4. The physical forces are not only convertible one into any of the others, but they are quantitively equivalent ; that is, a given amount of heat will produce an amount of light or of electricity, or of any other force, which, if it could be utilized, would reproduce precisely that amount of heat. A cannon-ball, when it impinges on a target, produces heat enough to give it the velocity which it had at the moment of contact. A certain amount of light and heat derived from the sun is expended in the formation of a certain amount of wood or coal ; that amount of wood or coal will furnish precisely the amount of light and heat which was expended in its production. Count Rumford experimented to determine the quan-
264' PART I.— THEOLOGY. [Cn. m.— Anti-Theism
titive relation between motion and heat, and arrived at very nearly the same conclusion as that reached by Dr. Joule of Manchester, England, who found that one pound of matter, falling seven hun- dred and seventy-two feet, will produce heat enough to raise the temperature of a pound of Avater one degree of Fahrenheit. This is now received as the unit of force.
5. Force is indestructible. It is never increased or diminished. What is lost in one form is taken up in another. Forces are, there- fore, indestructible, convertible, and imponderable agents. This correlation and conservation of forces is declared by Dr. Carpenter, tlie eminent physiologist, to be " now amongst the best established generalizations of physical science," and the greatest scientific triumph of the age ; " thanks," as he says, " to the labors of Fara- day, Grove, Joule, Thomson, and Tyndall, to say nothing of those of Helmholtz and other distinguished continental savans." ^
Correlation of the Physical and Vital Forces.
So long as this doctrine of the correlation of forces is confined to the department of physics, it is a purely scientific question, in which the theologian has no special interest. Unhappily it has not been thus confined. Dr. Carpenter, in the paper just quoted, says, " Every thoughtful physiologist must desire to see the same course of inquiry thoroughly pursued in regard to the phenomena of living bodies."^ The first step in that direction, he adds, was taken by Dr. Mayer of Germany, in his remarkable treatise on " Organic Movement in its Relation to Material Changes."
There appear to be three forms of opinion among scientific men, of the " advanced " school, as to the relation between vital and pliysical forces. First, there are some, of whom Dr. Carpenter is one, who hold that the forces by which vital processes are carried on, are light, heat, electricity, and so forth, but that these are directed or controlled by a force of a different kind, called " a directing agency."
Dr. Carpenter' s Theory. Dr. Carpenter denies that there is any such thing as vitality, or vital force, or nisus formativus, or Bildungstrieb. Two germs may be selected between which neither the microscope nor chem- ical analysis can detect the slightest difference ; yet one develops
1 See Correlation and Conservation of Forces. A collection of papers by distinguished icientific men. By Edward L. Youmans, M. D. New York, 1865, p. 405.
2 Ibid. p. 405.
§4, E.] MATERIALISM. ITS SCIENTIFIC FORM. 26j>
into a fish, another into a bird. Why is this? Dr. Carpenter answers because of a " directing agency " residing in the germ. His language is : " The prevalent opinion has until lately been, that this power is inherent in the germ ; which has been supposed to derive from its parent not merely its material substance, but a nisus formativus, Biklungstrieb, or germ-force, in virtue of which it builds itself up into the likeness of its parent, and maintains itself in that likeness until the force is exhausted, and at the same time imparting a fraction of it to each of its progeny." ^ This opinion he rejects ; but adds, " When we look carefully into the question, we find that what the germ really supplies, is not the force, but the directive agency ; thus rather resembling the control exercised by the superintendent builder, who is charged with working out the design of the architect, than the bodily force of the workmen who labor under his guidance in the construction of the fabric." ^ The conclusion at which he arrives is " that the correlation be- tween heat and the organizing force of plants is not less intimate than that which exists between heat and motion. The special attribute of the vegetable germ is its power of utilizing, after its own peculiar fashion, the heat which it receives, and of applying a constructive power to the building up of its fabric after its charac- teristic type." ^
On this doctrine of Carpenter it may be remarked, (1.) That it seems to be self-contradictory. He denies to the germ a nisus for- mativus, or, Bildungstrieb, and attributes to it "a constructive power." What is the difference ? The English phrase is a literal translation of the German word. (2.) He says that " heat and the organizing force of plants " are correlated, i. e., they are con- vertible one into the other and are quantitively equivalent; and yet the relation between them is analogous to that between a su- perintending builder and the strength of the workmen. According to this, the physical strength of the hod-man is convertible into the intellect of the builder and is its quantitive equivalent. We do not see how this contradiction is to be avoided, unless he uses the phrases " constructive force," " organizing force," sometimes for the "directing agency" in the germ, and sometimes, for the phys- ical forces which that agency controls. But if he distinguishes between the " directing agency " and " the organizing force," then there is no correlation between the physical force and " the vital activity of the germ."
1 See Correlation and Conservation of Forces, p. 411. 2 Jbid. p. 412.
« Jbid. p. 119. Also, New Quarterly Journal of Science for 1864.
266 PART L — THEOLOGY. [Ch. m. — Anti-Theism.