Popular Science Monthly/Volume 7/August 1875/Editor's Table
AMONG the higher influences of science to be realized in the future, will be its inculcation of more correct views concerning the relation of the human mind to truth. The effect of partisanship in politics and theology—the two great schools in which people are chiefly educated—is to establish the idea that truth is something absolute, that can be got once for all, and then can be comfortably held and professed forever afterward. There are only truth and its opposite error sharply divided off to choose from; and a "yes" or "no" is demanded for all propositions. In some things this is no doubt true; there is only one side to the multiplication-table. But, in extensive divisions of thought, truth is only a relative thing; of inestimable value for its time, and most of all valuable as a means of getting away from it and attaining more perfect truth. Logic is the art or science of arriving at truth by ratiocination; but science is the field where logic is put to practical application and subjected to the most rigorous tests. The human mind if left to logic alone may go wild in any direction; science holds it steadily to the observed order of Nature as the standard by which it is to be tried. The whole circle of the sciences bears witness to the correctness of scientific thinking; and the history of every science abounds in proofs of the relativity of truth. Certain parts of elementary facts may remain constant, but even the interpretations of these, true only for their time, are changed, age after age. The science of chemistry affords an admirable exemplification of this view.
There was vague and indefinite truth even in the chimeras of the alchemists, mixed indeed with an enormous amount of gross error and preposterous speculation as seen from subsequent points of view; but there was sufficient of verity and correspondence to reality in those mystical times to guide men to important discoveries. The alchemists found out a great number of new and valuable things. They worked under delusions, but these were far from being destitute of plausibility; and were in fact in no small measure consistent and rational. Experimental knowledge at any rate grew in extent, and somewhat in coherency, until the absurdities of the epoch fell away and a definite and rational chemical system ensued.
This was the epoch of Phlogiston which was held to be a kind of subtile matter or energetic essence, present in all combustible bodies and absent in all incombustible bodies, and which caused combustion-changes in its escape. It was a theory of the nature and cause of fire; and, as heat is implicated in nearly all chemical changes, it was a crude theory of chemical action. It served the most important uses. It was a principle of connection and association, and explication, which stimulated investigation, guided inquiry, and enlarged the domain of actual knowledge. A chemical belief that the discoverer of oxygen. Dr. Priestley, held to the day of his death, could certainly not have been an absurdity. Prof. Cooke has the following excellent remarks on this early theory: "That it was not absurd a single consideration will show. Translate the word phlogiston, energy, and in Stahl's work on chemistry and physics, of 1731, put energy where he wrote phlogiston, and you will find there the germs of our great modern doctrine of conservation of energy—one of the noblest products of human thought. It was not a mere fanciful speculation which ruled the scientific thought of Europe for a century and a half. It was a really grand generalization; but the generalization was given to the world clothed in such a material garb that it has required two centuries to unwrap the truth." Nevertheless there was invaluable truth in it, but truth obscured, imperfect, and in relation to the time.
The phlogistic doctrine broke down as the facts accumulated and outgrew it; and chemical science passed into a new phase. That which had long helped at length became an obstruction, and, with the abandonment of the entity, chemical effects began to be referred to inherent attractions among different kinds of matter. But the facts must still be interpreted by principles or theories, and, at the epoch of Lavoisier, affinity, or the energy of chemical change, was viewed simply as a coupling force. Combination and decomposition were supposed to take place directly among bodies in pairs; elements uniting with elements to form binary compounds, and these uniting again by twos to form double binary or ternary compounds, and when these were made to act on each other the reaction was represented as a double decomposition. This was known as the dual theory of chemistry, and it organized and explained the facts of the science in the most beautiful manner. Electro-chemistry lent it powerful aid, as compounds were resolved into pairs by galvanic decomposition, and their elements were supposed to be in opposite electrical states and to be united by polar attractions. The atomic theory gave a basis of philosophy to the doctrine, and the admirable nomenclature which was adapted to it gave it wide currency and acceptance. Under this chemical system the science grew and flourished for more than half a century, spread out into branches, and became the guide in medicine, mining, agriculture, and numberless arts and manufactures. Yet this system, too, was true for its time; only true in relation to the facts known, and is now doomed to the fate of phlogiston. As it grew out of a preceding stage upon which it was a great improvement, so it has led to a subsequent and higher stage of knowledge, to which it must, in turn give way. Its facts live on; its partial truths survive and are expanded into new forms, and a system of doctrine has arisen so contrasted with the dual theory and so advanced beyond it that it is now characterized as the "new chemistry" in contradistinction to the old which it has superseded. We are now entering upon the new chemical epoch in which ideas that have long simmered in the brains of chemists, and were long contested, have emerged into distinctness and are passing into predominance. The simple splitting and pairing theory of chemical change has failed, and we are becoming familiar with the conception of unitary structure, molecular types, and transformations by substitution and replacement that leave the construction and character of chemical compounds unaltered. The dualist appealed to analysis, and asked only what are the constituents and what their proportions in chemical substances. The apostles of the new chemistry point to the failures of analysis, and aver that it is not so much what a compound is made of, as how its elements are arranged, that is the present concern of inquiry. And chemistry was probably never so active as now under guidance of the new theories, and never before answered so well to that highest test of science, the prevision and prediction of chemical results. There is no escape from the new chemistry. It absorbs the verities of the past and it is the highest truth arrived at by centuries of thought and labor. But it is not a finality. Its truth, though priceless, is imperfect, and is no doubt destined to still further and higher development. Historically regarded, the science of chemistry is a striking exemplification of the laws of mental evolution, as the doctrine of evolution is the grandest illustration of the relativity of truth.
An interesting illustration of the striking changes of view that have taken place in modern chemistry is furnished by the reversal of scientific rank assigned to those prime elements of Nature, oxygen and hydrogen gases. Oxygen was long enthroned both from its enormous distribution in earth, sea, and air, and its active participation in the great changes of matter, combustion, respiration, decay, all of which were generalized as different forms and grades of oxidation. It was supposed to be the acidifying principle in Nature, and was early taken as a standard in chemical scales. Hydrogen was also known as a widely-diffused and important element, but of far inferior import to oxygen, and received its name from the fact that it generates water by union with oxygen. But, as more was known about it, it was found to be deeply implicated in the universal transformations of matter. It turned out that hydrogen not oxygen is the great acidifying principle, and not only so, but it is the base-producing principle, while the old and antagonizing classes of acids and bases disappeared as separate groups and were merged in one great division of hydrates. Hydrogen, moreover, by its remarkable properties and position has become the unit and standard of the modern chemical system, and, though less abundant upon earth than oxygen, it is the grand element of the sun, has been detected in the remotest stellar luminaries, in the mysterious nebulae, and blazed out in a mighty conflagration of one of the most distant stars. Such is the part played by that form of matter which is the most attenuated, ethereal, and "nearest to nothing," of any we know.