When

relations, it may, according to circumstances, at one time suggest one of these ideas, and at another time, a different one. we dwell long on the same idea, we obtain all the others to which it is any way related, and thus are furnished with materials on which our powers of judgment and reasoning may be employed. The effect of the division of labor in multiplying mechanical contrivances is to be explained partly on the same principle. It limits the attention to a particular subject, and familiarizes to the mind all the possible combinations of ideas which have any relation to it.

How invention differs from wit. These observations suggest a remarkable difference between invention and wit. The former depends, in most instances, on a combination of those ideas, which are connected by the less obvious principles of association; and it may be called forth in almost any mind by the pressure of external circumstances. The ideas which must be combined, in order to produce the latter, are chiefly such as are associated by those slighter connections, which take place when the mind is careless and disengaged. "If you have real wit," says Lord Chesterfield, "it will flow spontaneously, and you need not aim at it; for in that case, the rule of the gospel is reversed; and it will prove, seek, and you shall not find." Agreeably to this observation, wit is promoted by a certain degree of intoxication, which prevents the exercise of that attention which is necessary for invention in matters of science. Hence too it is, that those who have the reputation of wits, are commonly men confident in their own powers, who allow the train of their ideas to follow, in a great measure, its natural course, and hazard, in company, every thing, good or bad, that occurs to them. Men of modesty and taste seldom attempt wit in a promiscuous society; or if they are forced to make such an exertion, they are seldom successful. Such men, however, in the circle of their friends, to whom they can unbosom themselves without reserve, are frequently the most amusing and the most interesting of companions; as the vivacity of their wit is tempered by a correct judgment and refined manners; and as its effect is heightened by that sensibility and delicacy, with

which we so rarely find it accompanied in the common intercourse of life.

When a man of wit makes an exertion to distinguish himself, his sallies are commonly too far-fetched to please. He brings

his mind into a state approaching to that of the inventor, 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 circumstances 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 connection between our favorite pursuit, and all the materials with which experience and reflection have supplied us for the further prosecution of it.

II. Inventions facilitated by general rules. 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 show, to how great a degree invention depends on cultivation

and habit, even in those sciences in which it is generally supposed that every thing 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 unlike 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 à 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 labors in such a form, as they thought would be most likely to excite the admiration of their readers. The revival of the ancient analysis, by some late mathematicians in this country, has, in part, justified these remarks, by showing 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 original genius; and the method of analysis gives us no satisfaction with respect to the process by which they are obtained.

How new theorems are discovered. 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.

Success in scientific researches depends on method. - 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 shows, 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 altera

tions, 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 a work 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 excellences 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." -(Discourses by Sir Joshua Reynolds.)

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 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