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IN treating, on a former occasion, of the faculty of . Attention, I endeavoured to illustrate those intellectual processes, which, by often passing through the mind, come at length to be carried on with a rapidity that eludes all our efforts to remark it; giving to many of our judgments, which are really the result of thought and reflection, the appearance of instantaneous and intuitive perceptions. The most remarkable instance of such processes which the history of the human understanding affords, occurs in what are commonly called the acquired perceptions of sight; the theory of which has engaged the curiosity of many philosophers since the time of BerkeF f

ley, and seems to be now pretty generally understood. The other cases which I allude to are extremely analogous to these acquired perceptions, and are explicable on the same general principles. The most material difference consists in this, that the acquired perceptions of sight are common to the whole human race; the common necessities of our mature forcing every man to cultivate, from early infancy, the habits by which they are formed; whereas the greater part of our other acquired judgments, being the result of habits connected with particular professions or pursuits, are peculiar to certain classes of individuals. Next to the acquired perceptions of sight may be ranked, in point of rapidity, those processes of thought which pass through the mind, in the familiar operations of reading and of writing. In the former operation, the meaning of what we read seems to be seized at once with the instantaneousness of a perception. In the latter, as the train of our ideas proceeds, we find these ideas recorded upon paper, by an almost spontaneous movement of the hand;—a movement which has no more tendency to distract our attention, than the function of respiration, or the action of the heart. It is the familiarity alone of such phenomena that prevents the generality of men from reflecting on them with the wonder which they excite in the mind of the philosopher; and which will be found always to rise higher, in proportion to the accuracy of the analysis to which he subjects them. But it is not as a subject of wonder only that these phenomena ought to be regarded. The practical lesson which they suggest is of the highest importance; and is calculated to inspire us with new confidence and vigour, in the cultivation of whatever intellectual habits our situation in life may render it useful for us to possess. Such was the inference which was long ago drawn from them by Polybius, with a spirit of philosophical generalization, which is not often to be met with in ancient historians. “It would be easy,” says this mostjudicious writer, “to shew by instances, that many things which ap“pear, in the beginning, to be not only difficult, but “absolutely impracticable, are, in the course of time, “and by continued use, accomplished with the great“est ease. Among numberless instances, the art of" “reading may be mentioned as one of the clearest “and most convincing proofs of this remark. Take “a man who has never learned to read, but is other. “wise a man of sense; set a child before him who “has learned, and order him to read a passage in a “book. It is certain, that this man will scarcely “be able to persuade himself, that the child, as he “reads, must consider distinctly, First, the form of “all the letters; in the Next place, their power; “and, Thirdly, their connection one with another. “For each of these things requires a certain portion “of time. When he hears him, therefore, read four “or five lines together, without any hesitation, and “in a breath, he will find it very difficult to be-, “lieve that the child never saw the book before. “But if to the reading some gesture also should be “added; if the child should attend to all the stops,

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“ and observe all the breathings, rough and smooth, “it will be absolutely impossible to convince the man “that this is true. From hence, therefore, we may “learn, never to be deterred from any useful pursuit “by the seeming difficulties that attend it; but to “endeavour rather to surmount these difficulties by “practice and habit.” " A rapidity somewhat approaching to that which is exemplified in reading and writing, has frequently been acquired by those whose attention has been early and constantly directed to arithmetical computations. The quickness of that glance with which they are able to tell at once the sum resulting from the addition of long columns of figures, is incredible to those who have not witnessed it; and is not easily explicable by those who have. It is to an acquired rapidity of judgment, resembling what is exhibited in the preceding instances, that I am inclined to ascribe a remarkable circumstance in the intellectual endowments of Sir Isaac Newton, which that great man (if we may credit Whiston) seems to have thought connected with some original peculiarity of genius:–I allude to his intuitive perception of various mathematical conclusions, by no means obvious to ordinary understandings. As an example of this, a well-known property of the Ellipse is mentioned; t of which (though

* Hampton's Translation.—The above extract forms part of a very interesting discussion concerning the use of an ancient Telegraph.

+ That the parallelogram, formed by the tangents passing certainly by no means self-evident) Newton is said to have told his friend Mr Cotes, that he saw at once the truth, without the intermediation of any process of reasoning whatsoever. For an explanation of the fact, according to my idea of it, I must refer my readers to some observations which I have stated in the Philosophy of the Human Mind. At present I shall only add, as another circumstance which may occasionally mislead a mathematician in estimating the quickness of his own perceptions, That, after having once ascertained the connection between two propositions by a process of reasoning, and fixed this connection in the memory, the one proposition will, in future, suggest the other as its necessary and immediate consequence. In this manner, an experienced mathematician proceeds, as it were, by leaps, from one truth to another; and may sometimes mistake, for an intuitive judgment, a conclusion deduced from a long process of thought, now obliterated from the mind. Another instance of extraordinary rapidity of thought occurs in individuals who are daily conversant with mechanical inventions. Where a person, possessed of equal intellectual ability, would find himself bewildered and lost among the details of a machine, the practised mechanician comprehends, in an instant, all the relations and dependencies of the different parts. We are apt to ascribe this quickness to a difference of natural capacity; but it is, n

through the vertices of any two of its conjugate diameters, is al. ways of the same magnitude.

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