are equally incomprehensible; and that, for any thing we know to the contrary, the connection between the sensation and perception, as well as between the impression and the sensation, may be both arbitrary; that it is, therefore, by no means impossible, that our sensations may be merely the occasions on which perceptions are excited; and that, at any rate, the consideration of these sensations, which are attributes of mind, can throw no light on the manner in which we acquire our knowledge of the existence and qualities of bodies. (STEWART'S Philosophy of the Human Mind.)

Corol. From this view of the subject, it follows, that it is the external objects themselves, and not any species or images of these objects, that the mind perceives; and that, although, by the constitution of our nature, certain sensations are rendered the constant antecedents of our perceptions, yet it is just as difficult to explain how our perceptions are obtained by this means, as it would be upon the supposition that the mind were all at once inspired with them, without any concomitant sensations whatever. The information of the senses is as perfect, and gives as full conviction to the most ignorant, as to the most learned; and the conviction we have of their reality rests upon consciousness, a faculty that puts the poorest of mankind upon a level with the greatest. (See Art. 69. Obs.)

CHAPTER IV.

OF ATTENTION.

122. ATTENTION is the faculty which detains, for our examination, ideas or perceptions in the mind, and excludes other objects that solicit its notice.

Illus. When we are deeply engaged in conversation, or occupied with any speculation that is interesting to the mind, the surrounding objects do not produce in us the perceptions they are fitted to excite; or those perceptions are instantly forgotten. Thus, a clock may strike in the same room with us, without our being able the next moment to recollect whether we heard it or not.

123. In these, and similar cases, it is commonly taken for granted, that we really do not perceive the external object. But analogous facts may serve to prove that this opinion is not well founded.

Mus. 1. Thus, a person who falls asleep at church, and is suddenly awaked, is unable to recollect the last words spoken by the

preacher, or even to recollect that he was speaking. And yet, that sleep does not suspend entirely the powers of perception, may be inferred from this, that, if the preacher were to make a sudden pause in his discourse, every person who was asleep in the congregation would instantly awake.

Corol. In this case, therefore, it appears, that a person may be conscious of a perception, without being able afterwards to recollect it.

Illus. 2. When we read a book, especially in a language that is not perfectly familiar to us, we must perceive successively every different letter, and must afterwards combine these letters into syllables and words, before we comprehend the meaning of a sentence. This process, however, passes through the mind without leaving any trace in the memory.

3. It has been proved by optical writers, that in perceiving the distances of visible objects from the eye, there is a judgment of the understanding antecedent to perception. In some cases this judgment is founded on a variety of circumstances combined togetherthe conformation of the organs necessary for distinct vision-the inclination of the optic axes-the distinctness or indistinctness of the minute parts of the object—the distances of the intervening objects from each other and from the eye and, perhaps, on other circumstances besides these ;-and yet, in consequence of our familiarity with such processes from our earliest infancy, the perception seems to be instantaneous.

4. As a further illustration, we shall produce another instance of a nature still more familiar. It is well known (says Mr. Stewart, to whom, for authority's sake, I attribute the materials of which this chapter is composed), that our thoughts do not succeed each other at random, but according to certain laws of association, which modern philosophers have been at pains to investigate. It frequently happens, particularly when the mind is animated by conversation, that it makes a sudden transition from one subject to another, which, at first view, appears to be very remote from it; and that it requires a considerable degree of reflection, to enable the person himself, by whom the transition was made, to ascertain what were the intermediate ideas. A curious instance of such sudden transition is mentioned by Hobbs, in his Leviathan : "In a company (says he), in which the conversation turned on the civil war, what could be conceived more impertinent, than for a person to ask abruptly, What was the value of a Roman denarius? On a little reflection, however, I was easily able to trace the train of thought which suggested the question; for the original subject of discourse naturally introduced the history of the king, and the treachery of those who surrendered his person to his enemies; this again introduced the treachery of Judas Iscariot, and the sum of money which he received for his reward. And all this train of ideas passed through the mind of the speaker in a twinkling, in consequence of the velocity of thought." Upon this anecdote Mr. Stewart observes very justly, "It is by no means improbable, that if the speaker himself had been interrogated about the connection of ideas which led him aside from the original topic of discourse, he would have found himself, at first, at a loss for an answer.'

Corol. The three last illustrations furnish us with proof that a perception or an idea, which passes through the mind, may yet serve to introduce other ideas connected with it by the laws of associ

ation.

124. When a perception or idea passes through the mind, without our being able to recollect it the next moment, persons the most illiterate ascribe their want of memory to a want of attention.

Illus. Thus, in the instance already mentioned of the clock, (Illus. Art. 122.) a person, upon observing that the minute-hand had just passed twelve, would naturally say, that he did not attend to the clock when it was striking.

Corol. There seems, therefore, to be a certain effort of mind upon which, even in the judgment of those who make no pretensions to philosophy, memory in some measure depends; and this effort they distinguish by the name of attention.

125. The memory depends much on the degree of attention which we give it; and it seems essential to memory, that the perception of the idea which we would wish to remember, should remain in the mind for a certain space of time, and should be contemplated by it exclusively of every thing else; and that attention consists partly (perhaps entirely) in the effort of the mind to detain the idea or perception, and to exclude the other objects that solicit its notice. And though there may be some difficulty of ascertaining in what this act of the mind consists, every person must be satisfied of its reality from his own consciousness, and of its essential connection with the power of memory.

Obs. The several instances which have already been mentioned, of ideas passing through the mind without our being able to recollect them the next moment, were produced merely to illustrate the meaning which we annex to the word attention, and to recall to the recollection of the student a few striking cases, in which the possibility of carrying on a process of thought, which we are unable to attend to at the time, or to remember afterwards, is acknowledged in the received systems of philosophy.

126. Among the phenomena which appear to be very similar to those we have introduced, illustrative of the faculty of attention, and which are explicable in the same manner, may be classed the wonderful effect of practice in the formation of habits-one of the most curious circumstances in the human constitution.

Illus. A mechanical operation, for example, which we at first performed with the utmost difficulty, comes, in time, to be so familiar to

us, that we are able to perform it without the smallest danger of mistake; even while the attention appears to be completely engaged with other subjects. The truth seems to be, that in consequence of the association of ideas, the different steps of the process present themselves successively to our thoughts, without any recollection on our part, and with a degree of rapidity proportioned to the length of our experience; so as to save us entirely the trouble of hesitation and reflection, by giving us every moment a precise and steady notion of the effect to be produced.

127. In the case of some operations which are very familiar to us, we find ourselves unable to attend to the acts of the will by which they were preceded, or even to recollect those acts; but the circumstance of our inability to recollect our volitions, does not authorize us to dispute their possibility, any more than our inability to attend to the process of the mind, in estimating the distance of an object from the eye, authorizes us to affirm that the perception is instantaneous.

128. Habit differs from instinct, not in its nature, but in its origin; the last being natural, the first acquired. Both appear to operate without will or intention, without thought, and have therefore been called mechanical principles.

Illus. Thus, suppose a person who has a perfectly voluntary command over his fingers to begin to learn to play on the harpsichord. The first step is to move his fingers from one key to another, with a slow motion, looking at the notes, and exerting an express act of volition in every motion. By degrees the motions cling to one another, and to the impressions of the notes, in the way of association, the acts of volition growing less and less express all the time, till at last they become evanescent and imperceptible. For an expert performer will play from notes, or notions of notes, laid up in the memory; and at the same time carry on a train of thoughts in his mind quite different from the piece of music which he is playing, or even hold a conversation with another. Here, it appears, that those operations which have become habitual from long practice, preclude the possibility of recollecting every different volition of the mind; yet it is not to be doubted that there is an act of the will preceding every motion of each finger, since the most rapid performer can, when he pleases, play so slowly, as to be able to attend to every separate act of his will in the various movements of his fingers, and even to recollect those volitions afterwards; and he can gradually accelerate the rate of his execution, till he is unable to recollect these acts.

Corol. The operations in these two cases appear to be carried on precisely in the same manner, and differ only in the degree of rapidity; and when this rapidity exceeds a certain rate, the acts of the will are too momentary to leave any impression on the memory.

129. The corollary just drawn from this second illustra

tion, is supported by the analogy of many other facts in our constitution.

Illus. 1. Thus, an expert accountant can sum up, almost at a single glance of his eye, a long column of figures; nay, of farthings, pence, shillings, and pounds, at one and the same time;— he can tell the sum with unerring certainty, while, at the same time, he is unable to recollect any one of the figures of which that sum is composed; and yet nobody doubts that each of these figures has passed through his mind, or supposes that when the rapidity of the process becomes so great that he is unable to recollect the various steps of it, he obtains the result by a sort of inspiration.

2. It has been found, by actual trial, that it is possible to pronounce about two thousand letters in a minute, and though the inconceivable rapidity with which our intellectual operations proceed, render it impossible to discriminate the volitions of our mind, the articulation of every letter, in reading aloud, must be preceded by a separate volition. Here, then, we have evidence that the mind is so formed as to be able to carry on certain intellectual processes, in intervals of time too short to be estimated by our faculties; yet, were our powers of attention and memory more perfect than they are, so as to give us the same advantage in examining rapid events, which the microscope gives us for examining minute portions of extension, they would enlarge our views with respect to the intellectual world, no less than that instrument has with respect to the material.

130. As the great use of attention and memory is to enable us to treasure up the results of our experience and reflection for the future regulation of our conduct, it would have answered no purpose for the Author of our nature to have extended their province to those intervals of time, which we have no occasion to estimate in the common business of life. All the intellectual processes which have been mentioned, are subservient to some particular end, either of perception or of action; and it would have been perfectly superfluous, if, after this end were gained, the steps which are instrumental in bringing it about, were all treasured up in the memory such a constitution of our nature would have had no other effect but to store the mind with a variety of useless particulars.

131. In confirmation of these reasonings on the faculty of attention, the following illustration affords a more palpable instance than any that we have yet mentioned, of the rapidity with which the thoughts may be trained up, by practice, to shift from one thing to another.

Illus. 1. When an equilibrist balances a rod upon his finger, not only the attention of his mind, but the observation of his eye, is com