room for much future inquiry lies in this direction. The 'states of mind' which every psychologist believes in are by no means clearly apprehensible, if distinguished from their objects. But to doubt them lies beyond the scope of our natural-science (see p. 1) point of view. And in this book the provisional solution which we have reached must be the final word: the thoughts themselves are the thinkers.

CHAPTER XIII.

ATTENTION.

The Narrowness of Consciousness.-One of the most extraordinary facts of our life is that, although we are besieged at every moment by impressions from our whole sensory surface, we notice so very small a part of them. The sum total of our impressions never enters into our experience, consciously so called, which runs through this sum total like a tiny rill through a broad flowery mead. Yet the physical impressions which do not count are there as much as those which do, and affect our sense-organs just as energetically. Why they fail to pierce the mind is a mystery, which is only named and not explained when we invoke die Enge des Bewusstseins, 'the narrowness of consciousness,' as its ground.

Its Physiological Ground. Our consciousness certainly is narrow, when contrasted with the breadth of our sensory surface and the mass of incoming currents which are at all times pouring in. Evidently no current can be recorded in conscious experience unless it succeed in penetrating to the hemispheres and filling their pathways by the processes set up. When an incoming current thus occupies the hemispheres with its consequences, other currents are for the time kept out. They may show their faces at the door, but are turned back until the actual possessors of the place are tired. Physiologically, then, the narrowness of consciousness seems to depend on the fact that the activity of the hemispheres tends at all times to be a consolidated and unified affair, determinable now by this current and now by that, but determinable only as a whole. The ideas correlative to the reigning system of processes

are those which are said to 'interest' us at the time; and thus that selective character of our attention on which so much stress was laid on pp. 173 ff. appears to find a physiological ground. At all times, however, there is a liability to disintegration of the reigning system. The consolidation is seldom quite complete, the excluded currents are not wholly abortive, their presence affects the 'fringe and margin of our thought.

Dispersed Attention. Sometimes, indeed, the normal consolidation seems hardly to exist. At such moments it is possible that cerebral activity sinks to a minimum. Most of us probably fall several times a day into a fit somewhat like this: The eyes are fixed on vacancy, the sounds of the world melt into confused unity, the attention is dispersed so that the whole body is felt, as it were, at once, and the foreground of consciousness is filled, if by anything, by a sort of solemn sense of surrender to the empty passing of time. In the dim background of our mind we know meanwhile what we ought to be doing: getting up, dressing ourselves, answering the person who has spoken to us, trying to make the next step in our reasoning. But somehow we cannot start; the pensée de derrière la tête fails to pierce the shell of lethargy that wraps our state about. Every moment we expect the spell to break, for we know no reason why it should continue. But it does continue, pulse after pulse, and we float with it, until -also without reason that we can discover—an energy is given, something we know not what enables us to gather ourselves together, we wink our eyes, we shake our heads, the background-ideas become effective, and the wheels of life go round again.

This is the extreme of what is called dispersed attention. Between this extreme and the extreme of concentrated attention, in which absorption in the interest of the moment is so complete that grave bodily injuries may be unfelt, there are intermediate degrees, and these have been studied experimentally. The problem is known as that of

The Span of Consciousness.-How many objects can we attend to at once when they are not embraced in one conceptual system? Prof. Cattell experimented with combinations of letters exposed to the eye for so short a fraction of a second that attention to them in succession seemed to be ruled out. When the letters formed familiar words, three times as many of them could be named as when their combination was meaningless. If the words formed a sentence, twice as many could be caught as when they had no connection. "The sentence was then apprehended as a whole. If not apprehended thus, almost nothing is apprehended of the several words; but if the sentence as a whole is apprehended, then the words appear very distinct."

A word is a conceptual system in which the letters do not enter consciousness separately, as they do when apprehended alone. A sentence flashed at once upon the eye is such a system relatively to its words. A conceptual system may mean many sensible objects, may be translated later into them, but as an actual existent mental state, it does not consist of the consciousnesses of these objects. When I think of the word man as a whole, for instance, what is in my mind is something different from what is there when I think of the letters m, a, and n, as so many disconnected data.

When data are so disconnected that we have no conception which embraces them together it is much harder to apprehend several of them at once, and the mind tends to let go of one whilst it attends to another. Still, within limits this can be avoided. M. Paulhan has experimented on the matter by declaiming one poem aloud whilst he repeated a different one mentally, or by writing one sentence whilst speaking another, or by performing calculations on paper whilst reciting poetry. He found that "the most favorable condition for the doubling of the mind was its simultaneous application to two heterogeneous operations. Two operations of the same sort, two multiplications, two recitations,

or the reciting of one poem and writing of another, render the process more uncertain and difficult."

M. Paulhan compared the time occupied by the same two operations done simultaneously or in succession, and found that there was often a considerable gain of time from doing them simultaneously. For instance:

"I multiply 421 312 212 by 2; the operation takes 6 seconds; the recitation of four verses also takes 6 seconds. But the two operations done at once only take 6 seconds, so that there is no loss of time from combining them."

If, then, by the original question, how many objects can we attend to at once, be meant how many entirely disconnected systems or processes can go on simultaneously, the answer is, not easily more than one, unless the processes are very habitual; but then two, or even three, without very much oscillation of the attention. Where, however, the processes are less automatic, as in the story of Julius Cæsar dictating four letters whilst he writes a fifth, there must be a rapid oscillation of the mind from one to the next, and no consequent gain of time.

When the things to be attended to are minute sensations, and when the effort is to be exact in noting them, it is found that attention to one interferes a good deal with the perception of the other. A good deal of fine work has been done in this field by Professor Wundt. He tried to note the exact position on a dial of a rapidly revolving hand, at the moment when a bell struck. Here were two disparate sensations, one of vision, the other of sound, to be noted together. But it was found that in a long and patient research, the eye-impression could seldom or never be noted at the exact moment when the bell actually struck. An earlier or a later point were all that could be

seen.

The Varieties of Attention.-Attention may be divided into kinds in various ways. It is either to

a) Objects of sense (sensorial attention); or to