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26. Let us next consider Natural Objects, as seen by the eye of the naturalist, with a view to catalogue and exhaust all their properties and relations. The Mineral, Vegetable, and Animal Kingdoms, as objects of intellectual curiosity and rational explanation, present, in each of their individual specimens, that mixture of the sensible present with the associated absent, above exemplified in the class of tools or machinery. Each mineral, plant, or animal, is a bundle of impressions, of which the whole cannot be made present to the sense at one time; there being a series of actions upon other individuals to be included in the conception, and these usually held together with the assistance of language. The complication thus presented is a degree beyond the preceding group. In Mineral bodies, we have the concurrence of many attributes in each individual, some sensible, others experimental; and it is under the estranging influence of much diversity that all the classes have been formed. Thus, to take the Metals. Some of these have a very large extent of sameness, as tin, zinc, silver, and lead; so, there is a close resemblance between gold and copper, between iron and manganese. But when we come to mercury, a striking point of diversity starts forth; namely, the liquid form. The influence of this diversity, leading the mind away to water and liquids of every kind, would prevent the rise of metals to the view, but for the strong effect of the two qualities-lustre and weight or specific gravity, which, acting by themselves, could suggest by similarity only such substances as silver, lead, tin, &c. This concurrence of two striking points of sameness, overpowers the diverting influence of the liquid state, and brings mercury to the mind's eye side by side with the metals. But these bodies have been identified with others in the midst of still greater discordance. When Sir Humphrey Davy suggested that metallic substances are locked up in soda, potash, and lime, the identification in his mind proceeded upon resemblances purely intellectual; that is to say, making no appeal to the senses, but arrived at through indirect signs, and represented to the mind by tech

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nical symbols. He found a class of bodies that had a close agreement with one another, and were termed salts; he saw that some of these consisted of an acid and the oxide of a metal,-as sulphate of iron, nitrate of silver; others consisted of an acid and a substance called an alkali,-as sulphate of soda, nitrate of potash. Here there were a number of bodies brought together in the mind by general agreement; an oxide of a metal in these bodies suggested by similarity of function an alkaline substance, both having the property of neutralizing an acid and forming a salt; it was impossible, therefore, not to class together in one group all substances having this property, which was done before the time of Davy, under the name bases. He, then, by a bold venture, asserted that this common property of neutralizing acids, and making salts, grows out of a still closer identity of character, namely, a common composition; in other words, that the alkalies are oxides of metals too, and that therefore all the bases contain a metal and oxygen. On putting the suggestion to the proof, it was found to hold good; lustrous metallic substances were actually separated from soda, potash, &c.; and the identity made good to the sense as well as to the reason. But to trace identities of this nature, a highly intellectual conception is required to intervene; salts had to be considered, not as appealing to the touch, the taste, and the sight, but as compounded of ingredients represented to the mind by names, figures, and symbols. Had copperas been known only as it appears in a drysalter's store, no such identifications could have grown out of its comparison with other salts. It behoved to be known as sulphuric acid combined with oxide of iron, or symbolically as S O3 + Fe O, in order to see an analogy between it and Glauber's salts, similarly represented, SO+ Soda. The scientific identities proceed on scientific conceptions, that is to say, on artificial ways of expressing, by names, numbers, and symbols, the facts that experiment brings to light. The same research led to a stroke of identification that would have been utterly impossible to the common eye, namely, of hydrogen gas with the metals,—a gas with

a solid, the lightest substance in nature with the heaviest. Hydrogen occurs in connexions that suggest a metal by the force of similarity, as by its combining with oxygen, and entering into still higher compounds exactly as the metals do. The repugnance between the physical or more sensible properties of hydrogen (gaseous form and lightness) and the properties of the metals, kept back for a time, but did not in the end prevent, an identification on the property of combining chemically in the same manner as these. And in the artificial representations of chemical formulæ, the identity is such as to strike the mind very readily; but this representation was itself consequent on the recognition of similarity of function in the two cases. An acid is now represented chemically in the same form as a salt, hydrogen standing in the acid for the metal in the salt. Sulphuric acid is HO, S O3, the sulphate of iron Fe O, S O3.

27. To pass from the mineral world to the Vegetable. Plants may be identified on many different points, and the same plant falls into different groups of associates according to the feature that predominates in the mind, and determines the stroke of recall. What in the end has turned out the most valuable classification, has often repelled at the outset by obtrusive dissimilarities. In the first Classification of plants, the Trees of the forest would be grouped together, owing to easy identification through their prominent and imposing points of likeness. The Shrubs would make another class identified by the same superficial likeness. The apparently insignificant and artificial identifications made by Linnæus would be repellent to a common eye, and could spring only from minute dissection of the structure, bringing out features of identity hidden in the heart of the efflorescence. The Linnæan classification was properly a fetch of identity in the midst of the widest discordance; and the mental preparation for gaining this triumph of identification, in the midst of difficulties, was a shutting of the eye to the bold features that held all other minds captive, and a devoted study of the minute and concealed structure. Also, the identifying

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reach of similarity in such a mind must have been of a high order, to produce so great a change in the mode of looking at the whole vegetable world, to break down all the old classifications, and compel the adoption of others entirely at variance with them.

The vegetable world presents us with another example of pure attraction of Similarity. The analogy of the flower to the whole plant, first struck the mind of the poet Goethe, and was considered by botanists a luminous suggestion. He saw, in the arrangement of the leaves round a stem, the analogue of the circular arrangement of the petals of the flower, notwithstanding very great diversity of general appearance. So, in the leaf, Oken identified the plant. The branchings of the veins of the leaf are, in fact, a miniature of the entire vegetable, with its parent stem, branches, and ramifications. In the first suggestion of these identities, we have notable cases of the stroke of similarity through a dense medium of diversity. Such identifications (when proved to be genuine and not merely apparent or fanciful), cast new lights over a subject; simplifying what is complex, and giving a clue to what seemed a labyrinth.

28. Our next examples are from the Animal Kingdom. In the classification of animals, we find the stroke of identity falling first upon one class of attributes, as in the divisions. into quadrupeds, birds, and fishes; a minuter examination paves the way for a deeper resemblance; certain animals inhabiting the sea are excluded from the class of fishesas the whale, seal, and porpoise; and certain others that fly in the air (the bats for example) are excluded from the class of birds. This new classification, like the reform of Linnæus in the Vegetable world, proceeded on an investigation of structure, and a disregard of the startling differences that arrest the common eye. It was accomplished by the comparative anatomists of the last century, and is now fixed for ever in the minds of men, by the language expressing the divisions and subdivisions of the animal kingdom.

Numerous interesting comparisons have been discovered

between the different parts of animals taken individually. These have been termed homologies. One of the first suggestions is attributed to the fertile analogical brain of Oken. Walking one day in a forest, he came upon the bleached skull of a deer. He took it up, and was examining its Anatomical arrangement, when there flashed upon his mind an original identity. The skull, he said, was four vertebræ; in fact, the head was merely a continuation of the back bone, but so expanded and distorted as to throw a deep disguise over the fundamental sameness of structure. That disguise was now shot through, by a powerful fetch of similarity, in a mind prepared by previous knowledge for discovering such likenesses. Oken was evidently a man

that sat loose to the existing identifications of things. He had, moreover, a large endowment of general Similarity. It appears further that he had a strong belief in the simplicity of nature, that is to say, in the recurrence, or repetition, of the same structure and the same plan of working, in many various forms and in the most widely separated regions. His convictions on this point went far beyond the reality, as we may see from his writings; for of the many hundreds of analogies that he sets forth in his one work 'Physiophilosophy,' there are probably not twenty that are sound. The intellectual force of similarity in him was under no check or control. He never took any steps to prove the reality of a supposed identification. The identifying stroke of similarity, bringing together, for the first time, things that had previously been looked at in totally different connexions, is the first step in a discovery, but only the first step. It has to be followed up by the labour of comparing minutely all the different things whose resemblance is implied in the identification, and only after this examination is complete, and the result satisfactory, is the discovery realized. Hence the remark, 'he discovers that proves.' Honour belongs to the first suggestion of a discovery, if that suggestion was the means of setting some one to work to verify it, but the world must ever look upon this last operation as the crowning exploit.

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