1. He tells us that the belief in a changeless order of nature "is a kind of inspiration." "The passage from facts to principles (that is, the passage from our limited experience of uniformity to the affirmation of universal and permanent order) is called induction, which in its highest form is inspiration."[438] This, however, is poetry, and not science. This inductive inference embraces vastly more in the conclusion than is contained in the premises; the antecedent is limited, the consequent is unlimited; and the only warrant that Dr. Tyndall has for the violation of the most fundamental logical canon is "inspiration." But, whatever Dr. Tyndall may understand by this ambiguous phrase, it is certain that his own mind is not satisfied, and so he tries again.
2. He tells us that this belief rests upon the long-continued observations, registered experiences, and experimental verifications of a succession of scientific men, as Galileo, Torricelli, Pascal, Kepler, and Newton. But here again the experiences are limited, and do not justify a universal conclusion; and Dr. Tyndall himself is not satisfied. He says, "The scientific mind can find no repose in the mere registration of sequences in nature. The further question obtrudes itself with resistless might, Whence come the sequences? What is it that binds the consequent with the antecedent in nature?" What is it, we ask with redoubled earnestness and emphasis, which authorizes our drawing a universal conclusion from particular premises? "The truly scientific intellect never can attain rest until it reaches the FORCES by which the observed succession is produced.... Not until the relation between the forces and the phenomena has been established is the law of the reason rendered concentric with the law of nature, and not until this is effected does the mind of the scientific philosopher rest in peace."[439] Here we have "the law of the reason" substituted for "the highest form of inspiration," and we are curious to learn what this "law of the reason" is. Is it the principle, or law of causality—namely, that "all phenomena present themselves to us as the expression of power, and refer us to a causal ground?" But this law of the reason says nothing about uniformity. The same power may produce a diversity of effects. "Infinitely numerous and various universes might have been fashioned by the various distribution of the original nebulous matter, although the particles of matter should obey the one law of gravity."[440]
3. And, finally, Dr. Tyndall tells us that "The expectation of likeness [i. e., uniformity] in the procession of phenomena is not that on which the scientific mind founds its belief in the order of nature. If the force is permanent, the phenomena are necessary whether they resemble or do not resemble any thing that has gone before. Hence in judging of the order of nature our inquiry eventually relates to the permanence of force,"[441] or, as he elsewhere styles it, "the conservation of energy," which means "that no power can make its appearance in nature without an equivalent expenditure of some other power; that natural agents are so related as to be mutually convertible, but that no new agency is created."[442] Whether this is or is not a correct statement of the principle of the conservation of energy we shall see by and by. And now, after having hunted the game through many tortuous passages to its final burrow, what have we found? That the ultimate principle which justifies the belief or "assumption" that the laws of nature are so rigidly inflexible and the order of nature is so absolutely uniform that "personal volition can not mingle in or interfere with the economy of nature" is the principle of the conservation of energy.
The answer of Dr. Tyndall is now fully and clearly before our mental view, and we are prepared for the consideration of its logical validity. This answer may be conveniently divided into two propositions. First, personal volition, human or Divine, can not intermingle or in any way interfere with the economy of nature because her laws are inflexible and her order is uniform. Second, the ultimate principle which justifies the assumption that the laws of nature are absolutely inflexible and the order of nature is absolutely uniform is the principle of the conservation of energy. We shall consider this latter proposition first.
There are in this proposition three ambiguous terms, which have hitherto been the source of serious misapprehension; and unless we can attain to clearer and more definite conceptions, which shall be mutually accepted, the controversy will be interminable. These are the terms "nature," "laws of nature," and "uniformity of the order of nature." We have made the attempt in a previous chapter[443] to give precision and definiteness to the concepts which these terms should connote. Referring the reader to the chapter indicated, we shall here simply restate our results.
1. Nature is the aggregate or totality of all material or physical phenomena.[444] "Nature (nascor, to be born) means that which is produced or born."[445]
2. A Law of Nature is the statement of a certain uniformity observed in the relations among phenomena.[446] The laws of nature are "simply expressions of phenomenal uniformities, having no coercive power whatever."[447]
3. The Uniformity of the Order of Nature may mean either "uniformity of co-existence" or "uniformity of succession." "Uniformity of co-existence" means that the same substances must always have the same essential properties[448] and the same permanent relations to other substances, as, for example, every molecule of hydrogen must have the same properties, the same definite mass, the same periodic vibrations, and the same chemical affinities. If these were to be altered in the least, it would no longer be a molecule of hydrogen.[449] This is uniformity in the ultimate constitution of nature. "Uniformity of succession" means that the same or similar consequents will always be found to follow similar antecedents, or "the same causes will always be followed by the same effects,[450] as, for example, the combination of carbon and oxygen will always be followed by the evolution of heat, and heat will always melt ice." This is uniformity in the course of nature or the procession of phenomena. Belief in the constancy of the course of nature or the uniformity of causation is the general expectation that "the future will resemble the past."[451]