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.