[34] Elem. Geol. p. 17.
The modern nomenclature of chemistry implies the oxygen theory of chemistry. Hence it has sometimes been objected to. Thus Davy, in speaking of the Lavoisierian nomenclature, makes the following remarks, which, however plausible they may sound, will be found to be utterly erroneous[35]. ‘Simplicity and precision ought to be the characteristics of a scientific nomenclature: words should signify things, or the analogies of things, and not opinions.... A substance in one age supposed to be simple, in another is proved to be compound, and vice versâ. A theoretical nomenclature is liable to continual alterations: oxygenated muriatic acid is as improper a term as dephlogisticated marine acid. Every school believes itself to be in the right: and if every school assumes to itself the liberty of altering the names of chemical substances in consequence of new ideas of their composition, there can be no permanency in the language of the science; it must always be confused and uncertain. Bodies which are similar to each other should always be classed together; and there is a presumption that their composition is analogous. Metals, earths, alkalis, are appropriate names for the bodies they represent, and independent of all speculation: whereas oxides, sulphurets, and muriates are terms founded upon opinions of the composition of bodies, some of which have been already found erroneous. 297 The least dangerous mode of giving a systematic form to a language seems to be to signify the analogies of substances by some common sign affixed to the beginning or the termination of the word. Thus as the metals have been distinguished by a termination in um, as aurum, so their calciform or oxidated state might have been denoted by a termination in a, as aura: and no progress, however great, in the science could render it necessary that such a mode of appellation should be changed.’
[35] Elements of Chem. Phil. p. 46.
These remarks are founded upon distinctions which have no real existence. We cannot separate things from their properties, nor can we consider their properties and analogies in any other way than by having opinions about them. By contrasting analogies with opinions, it might appear as if the author maintained that there were certain analogies about which there was no room for erroneous opinions. Yet the analogies of chemical compounds, are, in fact, those points which have been most the subject of difference of opinion, and on which the revolutions of theories have most changed men’s views. As an example of analogies which are still recognized under alterations of theory, the writer gives the relation of a metal to its oxide or calciform state. But this analogy of metallic oxides, as Red Copper or Iron Ore, to Calx, or burnt lime, is very far from being self-evident;—so far indeed, that the recognition of the analogy was a great step in chemical theory. The terms which he quotes, oxygenated muriatic acid (and the same may be said of dephlogisticated marine acid,) if improper, are so not because they involve theory, but because they involve false theory;—not because those who framed them did not endeavour to express analogies, but because they expressed analogies about which they were mistaken. Unconnected names, as metals, earths, alkalis, are good as the basis of a systematic nomenclature, but they are not substitutes for such a nomenclature. A systematic nomenclature is an instrument of great utility and power, as the modern history of chemistry has shown. It would be highly unphilosophical to reject 298 the use of such an instrument, because, in the course of the revolutions of science, we may have to modify, or even to remodel it altogether. Its utility is not by that means destroyed. It has retained, transmitted, and enabled us to reason upon, the doctrines of the earlier theory, so far as they are true; and when this theory is absorbed into a more comprehensive one, (for this, and not its refutation, is the end of a theory so far as it is true,) the nomenclature is easily translated into that which the new theory introduces. We have seen, in the history of astronomy, how valuable the theory of epicycles was, in its time: the nomenclature of the relations of a planet’s orbit, which that theory introduced, was one of Kepler’s resources in discovering the elliptical theory; and, though now superseded, is still readily intelligible to astronomers.
This is not the place to discuss the reasons for the form of scientific terms; otherwise we might ask, in reference to the objections to the Lavoisierian nomenclature, if such forms as aurum and aura are good to represent the absence or presence of oxygen, why such forms as sulphite and sulphate are not equally good to represent the presence of what we may call a smaller or larger dose of oxygen, so long as the oxygen theory is admitted in its present form; and to indicate still the difference of the same substances, if under any change of theory it should come to be interpreted in a new manner.
But I do not now dwell upon such arguments, my object in this place being to show that terms involving theory are not only allowable, if understood so far as the theory is proved, but of great value, and indeed of indispensable use, in science. The objection to them is inconsistent with the objects of science. If, after all that has been done in chemistry or any other science, we have arrived at no solid knowledge, no permanent truth;—if all that we believe now may be proved to be false to-morrow;—then indeed our opinions and theories are corruptible elements, on which it would be unwise to rest any thing important, and which we might wish to exclude, even from our names. But if 299 our knowledge has no more security than this, we can find no reason why we should wish at all to have names of things, since the names are needed mainly that we may reason upon and increase our knowledge such as it is. If we are condemned to endless alternations of varying opinions, then, no doubt, our theoretical terms may be a source of confusion; but then, where would be the advantage of their being otherwise? what would be the value of words which should express in a more precise manner opinions equally fleeting? It will perhaps be said, our terms must express facts, not theories: but of this distinction so applied we have repeatedly shown the futility. Theories firmly established are facts. Is it not a fact that the rusting of iron arises from the metal combining with the oxygen of the atmosphere? Is it not a fact that a combination of oxygen and hydrogen produces water? That our terms should express such facts, is precisely what we are here inculcating.
Our examination of the history of science has led us to a view very different from that which represents it as consisting in the succession of hostile opinions. It is, on the contrary, a progress, in which each step is recognized and employed in the succeeding one. Every theory, so far as it is true, (and all that have prevailed extensively and long, contain a large portion of truth,) is taken up into the theory which succeeds and seems to expel it. All the narrower inductions of the first are included in the more comprehensive generalizations of the second. And this is performed mainly by means of such terms as we are now considering;—terms involving the previous theory. It is by means of such terms, that the truths at first ascertained become so familiar and manageable, that they can be employed as elementary facts in the formation of higher inductions.
These principles must be applied also, though with great caution, and in a temperate manner, even to descriptive language. Thus the mode of describing the forms of crystals adopted by Werner and Romé de l’Isle was to consider an original form, from which other forms are derived by truncations of the edges and the 300 angles. Haüy’s method of describing the same forms, was to consider them as built up of rows of small solids, the angles being determined by the decrements of these rows. Both these methods of description involve hypothetical views; and the last was intended to rest on a true physical theory of the constitution of crystals. Both hypotheses are doubtful or false: yet both these methods are good as modes of description: nor is Haüy’s terminology vitiated, if we suppose (as in fact we must suppose in many instances,) that crystalline bodies are not really made up of such small solids. The mode of describing an octahedron of fluor spar, as derived from the cube, by decrements of one row on all the edges, would still be proper and useful as a description, whatever judgment we should form of the material structure of the body. But then, we must consider the solids which are thus introduced into the description as merely hypothetical geometrical forms, serving to determine the angles of the faces. It is in this way alone that Haüy’s nomenclature can now be retained.
In like manner we may admit theoretical views into the descriptive phraseology of other parts of Natural History: and the theoretical terms will replace the obvious images, in proportion as the theory is generally accepted and familiarly applied. For example, in speaking of the Honeysuckle, we may say that the upper leaves are perfoliate, meaning that a single round leaf is perforated by the stalk, or threaded upon it. Here is an image which sufficiently conveys the notion of the form. But it is now generally recognized that this apparent single leaf is, in fact, two opposite leaves joined together at their bases. If this were doubted, it may be proved by comparing the upper leaves with the lower, which are really separate and opposite. Hence the term connate is applied to these conjoined opposite leaves, implying that they grow together; or they are called connato-perfoliate. Again; formerly the corolla was called monopetalous or polypetalous, as it consisted of one part or of several: but it is now agreed among botanists that those corollas which 301 appear to consist of a single part, are, in fact, composed of several soldered together; hence the term gamopetalous is now employed (by De Candolle and his followers) instead of monopetalous[36].
[36] On this subject, see Illiger, Versuch einer Systematischen Vollständigen Terminologie für das Thierreich und Pflanzenreich (1810). De Candolle, Théorie Élémentaire de la Botanique.