From this cursory view of the subject, it appears that we have a multitude of different successive perceptions in every moment of our existence.
-- To return.
Consciousness, as it has been above defined, appears to be one of the departments of memory. Now the nature of memory, so far as it relates to the subject of which we are treating, is obvious. An infinite number of thoughts passed through my mind in the last five minutes of my existence.
How many of them am I now able to recollect? How many of them shall I recollect tomorrow? One impression after another is perpetually effacing from this intellectual register. Some of them may with great attention and effort be revived; others obtrude themselves uncalled for; and a third sort are perhaps out of the reach of any power of thought to reproduce, as having never left their traces behind them for a moment. If the memory be capable of so many variations and degrees of intensity, may there not be some cases with which it never connects itself? If the succession of thought be so inexpressibly rapid, may they not pass over some topics with so delicate a touch as to elude the supplement of consciousness?
It seems to be consciousness, rather than the succession of ideas, that measures time to the mind. The succession of ideas is, in all cases, exceedingly rapid, and it is by no means clear that it can be accelerated. We find it impracticable in the experiment to retain any idea in our mind unvaried for any perceptible duration. Continual flux appears to take place in every part of the universe. Of thought, may be said, in a practical sense, what has been affirmed of matter, that it is infinitely divisible. Yet time seems, to our apprehension, to flow now with a precipitated, and now with a tardy course. The indolent man reclines for hours in the shade; and, though his mind be perpetually at work, the silent progress of time is unobserved. But, when acute pain, or uneasy expectation, obliges consciousness to recur with unusual force, the time appears insupportably long. Indeed it is a contradiction in terms to suppose that the succession of thoughts, where there is nothing that perceptibly links them together, where they totally elude the memory and instantly vanish, can be a measure of time to the mind. That there is such a state of mind, in some cases assuming a permanent form, has been so much the general opinion of mankind that it has obtained a name, and is called reverie. It is probable from what has been said that thoughts of reverie, understanding by that appellation thoughts untransmitted to the memory, perpetually take their turn with our more express and digested thoughts, even in the most active scenes of our life.
Lastly, thought may be the source of animal motion, and yet there may be no need of a distinct thought producing each individual motion. This is a very essential point in the subject before us. In uttering a cry for example, the number of muscles and articulations of the body concerned in this operation is very great; shall we say that the infant has a distinct thought for each of these articulations?
The answer to this question will be considerably facilitated if we recollect the manner in which the impressions are blended which we receive from external objects. The sense of feeling is diffused over every part of my body, IChapter eel the different substances that support me, the pen I guide, various affections and petty irregularities in different parts of my frame, nay, the very air that environs me. But all these impressions are absolutely simultaneous, and I can have only one perception at once. Out of these various impressions, the most powerful, or that which has the greatest advantage to solicit my attention, overcomes and drives out the rest; or, which not less frequently happens, some idea of association, suggested by the last preceding idea, wholly withdraws my attention from every external object. It is probable however that this perception is imperceptibly modified by the miniature impressions which accompany it, just as we actually find that the very same ideas presented to a sick man take a peculiar tinge which renders them exceedingly different from what they are in the mind of a man in health. It has been already shown that, though there is nothing less frequent than the apprehending of a simple idea, yet every idea, however complex, offers itself to the mind under the conception of unity. The blending of numerous impressions into one perception is a law of our nature; and the customary train of our perceptions is entirely of this denomination.
After this manner, not only every perception is complicated by a variety of simultaneous impressions, but every idea that now offers itself to the mind is modified by all the ideas that ever existed in it. It is this circumstance that constitutes the insensible empire of prejudice; and causes every object which is exhibited to a number of individuals to assume as many forms in their mine as there are individuals who view it.
These remarks furnish us with an answer to the long disputed question, whether the mind always thinks? It appears that innumerable impressions are perpetual!' made upon our body; and the only way in which the slightest of these is prevented from conveying a distinct report to the mind is in consequence of its being overpowered by some more considerable impression.