and becomes rather ingenious than witty. This is often the case with the writers whom Johnson distinguishes by the name of the metaphysical poets.

Those powers of invention which necessity occasionally calls forth in uncultivated minds, some individuals possess habitually. The related ideas which, in the case of the former, are brought together by the slow efforts of attention and recollection, present themselves to the latter, in consequence of a more systematical arrangement of their knowledge. The instantaneousness with which such remote combinations are effected sometimes appear so wonderful, that we are apt to ascribe it to something like inspiration; but it must be remembered, that when any subject strongly and habitually occupies the thoughts, it gives us an interest in the observation of the most trivial circumstance which we suspect to have any relation to it, however distant; and by thus rendering the common objects and occurrences which the accidents of life present to us subservient to one particular employment of the intellectual powers, establishes in the memory a connexion between our favourite pursuit and all the materials with which experience and reflection have supplied us for the farther prosecution of it.

II. I observed, in the second place, that invention may be facilitated by general rules, which enable the inventor to direct the train of his thoughts into particular channels. These rules (to ascertain which, ought to be one principal object of the logician) will afterwards fall under my consideration, when I come to examine those intellectual processes which are subservient to the discovery of truth. At present I shall confine myself to a few general remarks; in stating which I have no other aim than to shew to how great a degree invention depends on cultivation and habit, even in those sciences in which it is generally supposed that everything depends on natural genius.

When we consider the geometrical discoveries of the ancients, in the form in which they are exhibited in the greater part of the works which have survived to our times, it is seldom possible for us to trace the steps by which they were led to their conclusions; and, indeed, the objects of this science are so un

like those of all others, that it is not unnatural for a person when he enters on the study, to be dazzled by its novelty, and to form an exaggerated conception of the genius of those men who first brought to light such a variety of truths, so profound and so remote from the ordinary course of our speculations. We find, however, that even at the time when the ancient analysis was unknown to the moderns, such mathematicians as had attended to the progress of the mind in the discovery of truth, concluded a priori, that the discoveries of the Greek geometers did not, at first, occur to them in the order in which they are stated in their writings. The prevailing opinion was, that they had possessed some secret method of investigation, which they carefully concealed from the world, and that they published the result of their labours in such a form as they thought would be most likely to excite the admiration of their readers. O quam bene foret," says Petrus Nonius, " si qui in scientiis mathematicis scripserint authores, scripta reliquissent inventa sua eadem methodo, et per eosdem discursus, quibus ipsi in ea primum inciderunt; et non, ut in Mechanica loquitur Aristoteles de artificibus, qui nobis foris ostendunt suas quas fecerint machinas, sed artificium abscondunt, ut magis appareant admirabiles. Est utique inventio in arte qualibet diversa multum a traditione; neque putandum est plurimas Euclidis et Archimedis propositiones fuisse ab illis ea via inventas qua nobis illi ipsas tradiderunt." The revival of the ancient analysis, by some late mathematicians in this country, has, in part, justified these remarks, by shewing to how great a degree the inventive powers of the Greek geometers were aided by that method of investigation, and by exhibiting some striking specimens of address in the practical application of it.

The solution of problems, indeed, it may be said, is but one mode in which mathematical invention may be displayed. The discovery of new truths is what we chiefly admire in an

1 See some other passages to the to his Restoration of the Loci Plani same purpose, quoted from different of Apollonius Pergaus. writers, by Dr. Simson, in the preface

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original genius; and the method of analysis gives us no satisfaction with respect to the process by which they are obtained.

To remove this difficulty completely, by explaining all the various ways in which new theorems may be brought to light, would lead to inquiries foreign to this work. In order, however, to render the process of the mind, on such occasions, a little less mysterious than it is commonly supposed to be, it may be proper to remark, that the most copious source of discoveries is the investigation of problems, which seldom fails (even although we should not succeed in the attainment of the object which we have in view) to exhibit to us some relations formerly unobserved among the quantities which are under consideration. Of so great importance is it to concentrate the attention to a particular subject, and to check that wandering and dissipated habit of thought, which, in the case of most persons, renders their speculations barren of any profit either to themselves or to others. Many theorems, too, have been suggested by analogy; many have been investigated from truths formerly known by altering or by generalizing the hypothesis; and many have been obtained by a species of induction. An illustration of these various processes of the mind would not only lead to new and curious remarks, but would contribute to diminish that blind admiration of original genius, which is one of the chief obstacles to the improvement of science.

The history of natural philosophy, before and after the time of Lord Bacon, affords another proof how much the powers of invention and discovery may be assisted by the study of method; and in all the sciences, without exception, whoever employs his genius with a regular and habitual success, plainly shews that it is by means of general rules that his inquiries are conducted. Of these rules, there may be many which the inventor never stated to himself in words, and, perhaps, he may even be unconscious of the assistance which he derives from them; but their influence on his genius appears unquestionably from the uniformity with which it proceeds, and in proportion as they can be ascertained by his own speculations, or collected by the logician from an examination of his researches, similar powers

of invention will be placed within the reach of other men, who apply themselves to the same study.

The following remarks, which a truly philosophical artist has applied to painting, may be extended, with some trifling alterations, to all the different employments of our intellectual powers.

"What we now call genius begins, not where rules, abstractedly taken, end, but where known, vulgar and trite rules have no longer any place. It must of necessity be, that works of genius, as well as every other effect, as it must have its cause, must likewise have its rules; it cannot be by chance. that excellencies are produced with any constancy, or any certainty, for this is not the nature of chance; but the rules by which men of extraordinary parts, and such as are called men of genius, work, are either such as they discover by their own. peculiar observation, or of such a nice texture as not easily to admit handling or expressing in words.

"Unsubstantial, however, as these rules may seem, and difficult as it may be to convey them in writing, they are still seen and felt in the mind of the artist, and he works from them with as much certainty, as if they were embodied, as I may say, upon paper. It is true, these refined principles cannot be always made palpable, like the more gross rules of art; yet it does not follow, but that the mind may be put in such a train, that it shall perceive, by a kind of scientific sense, that propriety which words can but very feebly suggest."1

SECT. V. APPLICATION OF THE PRINCIPLES STATED IN THE FOREGOING SECTIONS OF THIS CHAPTER, TO EXPLAIN THE PHENOMENA OF DREAMING.

With respect to the Phenomena of Dreaming, three different questions may be proposed. First, What is the state of the mind in sleep? or, in other words, what faculties then continue to operate, and what faculties are then suspended? Secondly, How far do our dreams appear to be influenced by our bodily 1 Discourses, by Sir Joshua Reynolds.

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sensations; and in what respects do they vary, according to the different conditions of the body in health and in sickness? Thirdly, What is the change which sleep produces on those parts of the body with which our mental operations are more immediately connected; and how does this change operate, in diversifying so remarkably the phenomena which our minds then exhibit, from those of which we are conscious in our waking hours? Of these three questions, the first belongs to the Philosophy of the Human Mind; and it is to this question that the following inquiry is almost entirely confined. The second is more particularly interesting to the medical inquirer, and does not properly fall under the plan of this work. The third seems to me to relate to a subject which is placed beyond the reach of the human faculties.

It will be granted that, if we could ascertain the state of the mind in sleep, so as to be able to resolve the various phenomena of dreaming into a smaller number of general principles; and still more, if we could resolve them into one general fact; we should be advanced a very important step in our inquiries upon this subject, even although we should find it impossible to shew in what manner this change in the state of the mind results from the change which sleep produces in the state of the body. Such a step would at least gratify, to a certain extent, that disposition of our nature which prompts us to ascend from particular facts to general laws, and which is the foundation of all our philosophical researches; and, in the present instance, I am inclined to think that it carries us as far as our imperfect faculties enable us to proceed.

In conducting this inquiry with respect to the state of the mind in sleep, it seems reasonable to expect that some light may be obtained from an examination of the circumstances which accelerate or retard its approach; for when we are disposed to rest, it is natural to imagine that the state of the mind approaches to its state in sleep more nearly than when we feel ourselves alive and active, and capable of applying all our various faculties to their proper purposes.

In general, it may be remarked that the approach of sleep is