seasons and crops, the pointing of the loadstone to the north, many of the causes of agreeable and disagreeable sensation and of good and ill health, the influences of national prosperity. A third class demand artificial media and aids, as Kepler's laws, and the law of refraction of light, which could not have been discovered without the intervention of numerical and geometrical relations.

III. DEDUCTION, Deductive Inference, Ratiocination, Application or Extension of Inductions, Syllogism. When an Inductive generality has been established, the application of it to new cases is called Deduction. Kepler's laws were framed upon the six planets; they have been deductively applied to all that have since been discovered. The law of gravity was deductively applied to explain the tides.

Deduction also is a process of identification, by the force of Similarity. The new case must resemble the old, otherwise there can be no legitimate application of the law. Newton, by an inductive identification, detected, among transparent bodies, a conjunction between combustibility and high refracting power; the oils and resins bend light much more than water or glass. He then, by a farther stroke of identification, bethought himself of the diamond, the most refracting of all known substances; the deductive application of the law would lead to the inference that it was composed of some highly combustible element; which afterwards was found to be the case.

The Deductive process appears under two aspects; a principle may be given, and its application to facts sought for; or a fact may be given, and its principle sought for. In both,

the discovery is made by the force of Similarity. When the law of definite proportions was first promulgated, an unbounded range of applications lay before the chemist; which was the carrying out of the principle deductively.

Reasoning by Analogy. This is a mode of reasoning that bears upon its name the process of Similarity; the fact, however, being that in it the similarity is imperfect, and the conclusion so much the less cogent. When we examine a sample of wheat, the production of the same soil, and infer that the rest will correspond to the sample, we make a rigid induction; there being an identity of nature in the material or kind. But when we reason from wheat to the other cereals, the similarity is accompanied with diversities, and the reasoning is then precarious and only probable; such is reasoning by Analogy. Thus, there is an analogy, not an identity, be

tween waves of water and waves of air as in sound; between electricity and the nerve force; between the functions, bodily and mental, of men and of the inferior animals; between the family and the state; between the growth of a living being and the growth of a nation. These analogies are struck out by the intellectual power of Similarity; they are useful when no closer parallelism can be drawn.

17. The scientific processes, named Induction and Deduction, correspond to what is called the REASON, or the Reasoning faculty of the mind.

The name Reason is used in a narrow sense, corresponding to Deduction, and also in a wider sense, comprising both Deduction and Induction. To express the scientific faculty in its fulness, the process called Abstraction would have to be taken along with Reason in the wider sense. What is variously termed by Hamilton the Elaborative or Discursive Faculty, Comparison, the Faculty of Relations, Thought (in a peculiar narrow sense), includes the aggregate of processes now described as entering into the operations of science. It has just been seen, that the working of Similarity renders an adequate account of the principal feature in all these operations, although, to complete the explanation, there still remains a circumstance to be brought forward under the head of the Constructive operations of the Intellect.

BUSINESS AND PRACTICE.

18. Of Practical discoveries, some are due to observation and trial; others are the extension or application of known devices, through the perception of Similarity.

The first discovery of a lever, a pump, or a boat, could be made only by a stumbling and tentative method; accident alone could disclose the advantage of these implements. But the extension, to new cases, of machinery once discovered, proceeds on the identifying stroke of Similarity, sometimes in the midst of great dissimilarity. Among early nations, we find few indications of discoveries by this last method; the mechanical knowledge of the Egyptians, or of the Chinese, would seem to be all of tentative or experimental origin. In modern invention, however, we can trace the workings of great intellectual force of Similarity. It is eminent in the career of Watt. His ' governor balls' is a wonderful stroke of intellectual grasp; it was not a mechanical tenta

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tive; it was not even the extension of a device already in existence. The similarity lay deeper; he wanted to institute a connexion between the increase or diminution of a rapid rotatory movement and the opening and shutting of a valve; and he was so fortunate as to recall the situation of bodies flying off by centrifugal force, where the distance from the centre varies slightly according to the change of speed. No other apposite parallel has ever been suggested for the same situation; and the device once thought of has been carried out into many different applications. His suggestion of the lobster-jointed pipe, for conveying water across the bottom of the Clyde, was another pure fetch of similarity.

The device of carving a mould and impressing it upon any number of separate things, goes back to a high antiquity; as we see in coins. One of its many extensions is the art of Printing.

The common water pump, discovered by experiment, was transmuted into the air pump. The water-wheel is the prototype of the ship's paddle. The screw-propeller is an extension of the vanes of the windmill.

In the administration and the forms of business, something must first be devised by trials, or suggested by accident; the further extension is a purely intellectual process. The organization of masses of men to act together began, doubtless, in the necessities of war; repeated trials showed that there must be a chief or superior head, with subordinate grades of command. The machinery once suggested is extended to all other organizations of large bodies, as for public works, manufactures, &c.

The arts of book-keeping, including the employment of printed forms and schedules, have been gradually made to permeate all departments of business.

The art of Persuasion is greatly dependent on the attractive force of Similarity. The orator has to make out an identity between his end and the views, opinions, and motive forces of his hearers; and such identity may be very much clogged and disguised. If he has to address an assembly of men of wealth, he must reconcile his aims with the rights and interests of property. Now, all reconciliation proceeds on the perception of points of agreement, real or supposed; hence a mind fertile in discoveries of identification is so far fitted for the task of persuasion. Burke's speeches abound in these strokes of discernment.

ILLUSTRATIVE COMPARISONS AND LITERARY ART.

19. A large department of invention, more especially in Literature, consists in striking out similitudes, among things different in kind, yet serving to illustrate each other.

Of the Figures of Speech, one extensive class is denominated Figures of Similarity, including the Simile, Metaphor, Personification, Allegory, &c. These are called Figures, because they proceed upon some likeness of form in difference of subject. When we compare the act of eating in a man and in a dog, the comparison is real, literal, a comparison in kind; when we talk of digesting and ruminating knowledge, the comparison is illustrative or figurative. Since the origin of literature, many thousands of such comparisons have been struck out; every great literary genius has contributed to the stock; the profusion of Shakespeare being probably unmatched.

These illustrative comparisons are of two kinds, depending, for their invention, on different mental conditions. Of the first kind are those that render an obscure subject clearer, as when we compare the heart to a force pump, the lungs to a bellows, and business routine to a beaten track. The expositor of difficult subjects and doctrines avails himself, as far as his intellectual reach will go, of such illustrative similitudes. They are numerous in Plato. Among the moderns, Bacon is conspicuous for both the number and felicity of his illustrations. Some have become household words. His Essay on Delays' may be referred to, as exemplifying his profuse employment of similes.

The invention of such similes is a pure intellectual effort of Similarity. They suppose previous acquaintance with the regions whence they are drawn, an acquaintance terminating in deep or vivid impressions, enhanced by a sensibility for the material of them.

The other class comprehends those serving for ornament, or emotional effect; as when one man is extolled as god-like, another compared to the brutes. Here the likeness involves a common emotion, with or without intellectual similitude. For their invention, a deep emotional susceptibility must be combined with the force of intellect. He that would command similitudes illustrative of a pathetic situation, must have often been pathetically moved in actually contemplating the original objects of comparison.

An unlearned genius like Bunyan knows the commoner appearances of nature, the experience of the mind open to every one, the more familiar aspects of society and manners, and the compass of religious doctrine. Out of these materials, Bunyan drew his similes and his allegories; being favoured by a special susceptibility to the concrete world of sense, by strong emotions superadding an element of interest to a greater or less number of objects, and, we must suppose also, by large general power of Similarity.

Shakespeare, without being learned, had more reading than Bunyan. Still his resources were to a great degree personal observation, and common things. His glances around him impressed the things on his mind with a force out of all proportion to the attention that he could have given them. Natural scenery, natural objects, human character, his own mind, society and its usages, were absorbed by him, as material for his identifying and constructive faculty. He had a moderate knowledge of books, which extended his sphere of allusion to foreign scenes, and to the incidents and personalities of the ancient world; and his study of the subject of one play gave him a stock of allusive references to be employed incidentally in the others.

Bacon had an eye for the concrete world about him, but his mental attention was divided between this and book study in philosophy, scholarship, politics, and law. His sphere of similitudes has a corresponding compass.

Milton also had the concrete eye for the real world, a poet's interest in nature, and a vein of emotion that gave special impressiveness to whatever was large, vast, unbounded, mysterious in its immensity. He likewise had very great stores of reading, and had absorbed the scenes and pictures of remote countries and times.

Literary comparisons being expressed in language, are very much subject to verbal conditions. The associations with words concur to bring some forward, and to keep others back. A great poet needs verbal profusion, as well as pictorial suggestiveness.

THE FINE ARTS IN GENERAL.

20. The intellectual power of tracing similarity in diversity is most conspicuous in Poetry and the Literary Art. It may enter, in some degree, into Painting, Sculpture, Architecture, and Design. But, as regards the