reveal the operation of the principle before us, in striking out deep identities in superficial diversities. In the first classifications of plants, the more obvious feature of size took hold of the attention; the Trees of the Forest, were marked off from the Shrubs, and the Flowers. The great step made by Linnæus, consisted in tracing identity in less conspicuous parts of the plant, the organs of fructification; under which the largest trees and the smallest shrubs were brought together.

Botany presents other examples. Thus, Goethe saw in the flower the form of the entire plant; the circular arrangement of the petals of the corolla was paralleled by the corkscrew arrangement of the leaves round the stem. So, Oken, in the leaf, identified the plant; the branchings of the veins of a leaf are, in fact, a miniature of the entire vegetable, with its parent stem, branches and ramifications.

In the Animal Kingdom, we might quote many deep fetches of Similarity. The first superficial classification of animals according to their element, animals of the land, the water, and the air, has since been traversed by other classifications founded on deep community of structure; the bat has been detached from birds, and the seal, whale, and porpoise from fishes. More pointed still, as illustrating the power of a few select minds to detect similarities unapparent to the multitude, is the discovery of the deep identities in the vertebrate skeleton, termed homologies. The first suggestion of them is attributed to Oken, a man remarkable for this species of intellectual penetration. Walking one day in a forest, he came on the blanched skull of a deer. He took it up, and while examining the anatomical arrangements, there flashed upon him the identity between it and the back bone; the skull, he said, was four vertebræ distorted by the expanded cerebral mass and the development of the face. It is strange that this similarity should not have been first struck out in the case of the fishes, where the deviation of the head from the spine is smallest. To see it in the quadruped, was to work at a far greater disadvantage. But Oken was a man, not merely gifted with large powers of analogical discovery, or, as one should say, general Power of Similarity; he was, by the bent of his mind, an analogy-hunter; he studiously set himself to look at things in diverse aspects, so as to detect new analogies. No man ever suggested so many identities of that peculiar class; although only a small number, perhaps not above half a dozen, have been found to hold upon farther examination.

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The homologies of the vetebrate series of animals, whose discovery and exposition enter into Comparative Anatomy, consist in showing the deep correspondence of parts superficially unlike; the upper arm of man, the fore leg of the quadruped, the wing of the bird, the anterior fin of the fish.

SUCCESSIONS.

15. The natural successions have been already considered under Cycle, Evolution, and Cause and Effect. In all of them, there is scope for Identification in the midst of difference.

Cycle. The chief natural phenomena of cycle, the day and the year, are too obviously alike not to be identified; the differences are insignificant as compared with the agreements. In the rising and setting of the stars, there is a point of similarity that may have been long unobserved, the constancy of angle in the same latitude, the angle being the co-latitude of the place. Besides being an unobvious fact, there are two disguising unlikenesses in the rising and setting of the stars in the same place; namely, the height reached by them, and the change of the time of rising throughout the year. The cycles of the planets would be easy to trace in the superior planets, not so in Mercury and Venus.

The cycles of human affairs are sometimes apparent, but often obscure. Writers on the Philosophy of History have remarked a sort of vibratory tendency in human societies, or a transition between two extremes, as from asceticism to licence, from severity of taste to laxity, from conservation to innovation.

Evolution. The successions of Evolution are typified, and principally constituted, by the growth of living beings. Each plant and animal, in the course of its existence, presents a series of phases, and, as respects these, we discover a similarity in different individuals and species. The department, called Comparative Embryology, traces identities in the midst of wide diversities. Again, the mental evolution of human beings is a subject of interesting comparison.

Cause and Effect. Causation is the name for the total productive forces of the world, and, as these are comparatively few in number, but wide in their distribution, and often disguised in their operation, the ingenuity of man has long been exercised in detecting the hidden similarities. An example will show the nature of the difficulties and the means of conquering them. The burning of coal, and the rusting of iron,

show to the eye nothing in common except the fact of change. No mere force of Similarity, however aided by the ordinary favouring conditions, positive and negative, could have detected the deep community of these two phenomena. Other phenomena had to be interposed, having relations to both, in order to disclose the likeness. The experiments of Priestley upon the red oxide were the intermediate link. Mercury, when burned, becomes heavier, being converted into a red powder, by taking up material from the air, which can be again driven off by heat, so as to reproduce the metallic substance. Thus, while the act of combustion of the mercury has a strict resemblance to the burning of coal, the resulting change on the substance could suggest the rusting of iron, the only difference being the time occupied. By such intermediate comparisons, the general law of oxidation has been gradually traced through all its entanglements.

If not the greatest known stretch of identifying genius, the example most illustrious from its circumstances was the discovery of universal gravitation. Here the appearances were, in the highest degree, unfavourable to identification. Who could see anything in common between the grand and silent march of the moon and the planets round the heavens, and the fall of unsupported bodies to the ground? A preparatory process was necessary on both sides. Newton, by studying the planetary motions as a case of the composition of forces, resolved them each into two; a tendency in a straight line through space, and a tendency to the sun as a centre. He thus had clearly before him the fact, that there was an attraction of the planets to the sun, and of the moon to the earth. This was the preparation on one side. On the other side, he meditated on the various phenomena of falling bodies, and, putting away as irrelevant the accidental circumstances and interests that engross the common mind, he saw in these bodies a common tendency of the nature of attraction to the earth's surface, or rather the earth's centre. Viewed in this light, the phenomenon was closely assimilated to the great effect of Solar attraction, which he had previously isolated; and we are not to be surprised that, in some happy moment, the two flashed together in his mind. Even after the preparatory shapings on both sides, the stroke of identification was a remarkable fetch of similarity; the attendant disparities were still great and imposing; and we must suppose that the mind of Newton was distinguished no less by the negative condition of inattention to the vulgar and sensuous aspects,

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than by absorption in the purely dynamical aspect, of the phenomena.

REASONING AND SCIENCE IN GENERAL.

16. The Generalizing power of the mind, already seen to be a mode of Similarity, culminates in Science, and is designated under the names Abstraction and Reasoning.

The example just quoted, and others previously given, exhibit Similarity at work in scientific discovery. Still, it is desirable to give a more complete view of the relations of science to the identifying faculty. The chief scientific processes are these four-Observation, Definition, Induction, Deduction; the first is the source of the individual facts, and depends on the senses; the three last relate to the generalities, and are all dependent on the intellectual force of Similarity.

I. Classification, Abstraction, Generalization of Notions or Concepts, General Names, DEFINITION. These designations all refer to the one operation of identifying a number of things on some point, or property, which property is finally embodied in language by the process called Definition. The start is given by an identifying operation, a perception of likeness or community in many things otherwise diverse. In watching the heavenly bodies, the early astronomers discovered a few that moved steadily through the fixed stars, and made the circle of the heavens in longer or shorter periods. The bodies identified and brought together on this common ground, made a class, as distinguished from a mere confused aggregate. The mind, reflecting on the things so classified, attends to their similarity, and ondeavours to leave out of view the points of dissimilarity; this is the long-disputed process of abstraction; the common attribute or attributes is called the abstract idea, the notion, or the concept. When a name is applied to the things compared, because of their agreement or community, it is a general name, as 'planet.' And when we are further desirous of settling, by the help of language, the precise nature and limits of the common attribute, the result is a definition. A planet would now be defined as 'a body circulating around the sun as its centre, in an orbit nearly circular.' (On ABSTRACTION, see Chap. v.)

II. Conjoined properties generalized, General Affirmations, Propositions, Judgments, Laws of Nature, INDUCTION. In Abstraction, a single isolated property, or a collection of proper

ties treated as a unity, is identified and generalized; under Induction, a conjunction, union, or concurrence of two distinct properties is identified. A proposition contains two notions bound together by a copula. 'Heat' is the name of one general property or notion; 'expansion' is the name of a second notion; the proposition 'heat expands bodies,' is a proposition uniting the two properties in an inductive generality, or a law of nature. Here, too, the prime requisite is the identifying stroke of Similarity. One present instance of the concurrence of heat with increase of bulk, may recall by similarity other instances; the mind, awakened by the flash of identity, takes note of the concurrence, looks out for other cases in point, and ventures (rightly or wrongly) to affirm a general law of nature, connecting the two properties.

All the difficulties and the facilities connected with the working of Similarity may be found attending these inductive generalizations. There is one noticeable circumstance special to the case. That two things or two properties affect us together, excites no attention at first; we are so familiar with such unions that we take little note of the fact. It is, however, a point of some importance to know whether two things, occurring together, do so merely by accident, or by virtue of some fixed attachment keeping them always together; for, in the first case, the coincidence is of no moment, while in the last case, it is something that we may count or and anticipate in the future. Now, the real problem of inductive generalization consists in eliminating the regular and constant concurrences from the casual and inconstant. It is the identifying stroke of Similarity that is the means of rousing us to the constant concurrences; these repeat themselves while other things come and go, and the repetition is the prompting to suspect an alliance, and not merely a coincidence.

The favouring conditions of mind for scientific induction are the conditions, positive and negative, of the scientific intellect on the whole. General Power of Similarity being supposed, the special circumstances are, susceptibility to symbols and forms; the previous familiarity with the subject matter; the scientific interest; and the absence of the purely sensuous and concrete regards. Such are unquestionably the intellectual features of the greatest scientific geniuses, the men whose lives are a series of discoveries.

Some conjunctions are obvious; as light and heat with the sun's rays. Others are less obvious, but yet discernible, without any artificial medium; such are the signs of weather,