Let us now, for the application of these remarks, consider, what it is which takes place in attention, when many objects are together acting on our senses, and we attend, perhaps, only to a single sensation. As a mere description of the process, I cannot use a happier exemplification, than that which Condillac has given us in his Logique.
Let us imagine a castle, which commands, from its elevation, an extensive view of a domain, rich with all the beauties of nature and art. It is night when we arrive at it. The next morning our window-shutters open at the moment when the sun has just risen above the horizon,—and close again the very moment after.
Though the whole sweep of country was shewn to us but for an instant, we must have seen every object which it comprehends within the sphere of our vision. In a second or a third instant we could have received only the same impressions which we received at first; consequently, though the window had not been closed again, we should have continued to see but what we saw before.
This first instant, however, though it unquestionably shewed us all the scene, gave us no real knowledge of it; and, when the windows were closed again, there is not one of us who could have ventured to give even the slightest description of it,—a sufficient proof, that we may have seen many objects, and yet have learned nothing.
At length the shutters are opened again, to remain open while the sun is above the horizon; and we see once more what we saw at first. Even now, however, if, in a sort of ecstacy, we were to continue to see at once, as in the first instant, all this multitude of different objects, we should know as little of them when the night arrived, as we knew when the window shutters were closed again after the very moment of their opening.
To have a knowledge of the scene, then, it is not sufficient to behold it all at once, so as to comprehend it in a single gaze; we must consider it in detail, and pass successively from object to object. This is what Nature has taught us all. If she has given us the power of seeing many objects at once, she has given us also the faculty of looking but at one,—that is to say, of directing our eyes on one only of the multitude; and it is to this faculty,—which is a result of our organization, says Condillac,—that we owe all the knowledge which we acquire from sight.
The faculty is common to us all: and yet, if afterwards we were to talk of the landscape which we had all seen, it would be very evident, that our knowledge of it would not be exactly the same. By some of us, a picture might be given of it with tolerable exactness, in which there would be many objects such as they were, and many, certainly, which had very little resemblance to the parts of the landscape which we wished to describe. The picture which others might give, would probably be so confused, that it would be quite impossible to recognize the scene in the description, and yet all had seen the same objects, and nothing but the same objects. The only difference is, that some of us had wandered from object to object irregularly, and that others had looked at them in a certain order.
Now, what is this order? Nature points it out to us herself. It is the very order in which she presents to us objects. There are some which are more striking than others, and which, of themselves, almost call to us to look at them; they are the predominant objects, around which the others seem to arrange themselves. It is to them, accordingly, that we give our first attention; and when we have remarked their relative situations, the others gradually fill up the intervals.
We begin, then, with the principal objects; we observe them in succession; we compare them, to judge of their relative positions. When these are ascertained, we observe the objects that fill up the intervals, comparing each with the principal object, till we have fixed the positions of all.
When this process of successive, but regular observation, is accomplished, we know all the objects and their situations, and can embrace them with a single glance. Their order, in our mind, is no longer an order of mere succession; it is simultaneous. It is that in which they exist, and we see it at once distinctly.