attribute to the “ uniformity of nature. ” If we never had the same series of impressions twice, knowledge of time would be impossible, as indeed would knowledge of any sort. 28. Time is often figuratively represented as a line, and we may perhaps utilize this figure to make clear the relation of our perception of time to what we call time itself. The Succession. . .
present, though conceived as a point or instant of time, is still such that we actually can and do in that moment attend to a plurality of presentations to which we might otherwise have attended to severally in successive moments. Granting this implication of simultaneity and succession, we may, if we represent succession as a line, represent simultaneity as a second line at right a.ngles to the first; pure time-or time-length without time-breadth, we may say- is a mere abstraction. Now it is with the former line that we have to do in treating of time as it is (or as we conceive it), and with the latter in treating of our perception of time, where, just as in a perspective representation of distance, we are confined to lines in a plane at right angles to the actual line of depth. In a succession of events A B C D E . the presence of B means the absence ofA and of C, but the presentation of this succession involves the simultaneous presence, in some mode or other, of two or more of the presentations A B C D. In our temporal perception, then, all that corresponds to the differences of past, present and future is presented simultaneously. To this fact the name of “ specious present” or “ psychical present ” has been given. What we have is not a moving point or moment of objective time, but rather a moving line, the contents of which, continuously changing, simultaneously represent a portion of the line of objective succession, viz. the immediate past as still present in primary memory-images, and the immediate future as anticipated in prepercepts and nascent acts.1 This truism-or paradox-that all we know of succession is but an interpretation of what is really simultaneous or coexistent, we may then concisely express by saying that we are aware of time only through time-perspective, and experience shows that it is a long step from a succession of presentations to such presentation of succession. The first condition of such presentation is that we should have represented together presentations that were in the first instance attended to successively, and this we have both in the persistence of primary memory-images and in the simultaneous reproduction of longer or shorter portions of the memory-train. In a series thus secured there may be time-marks, though no time, and by these marks the series will be distinguished from other simultaneous series. To ask which is first among a number of simultaneous presentations is unmeaning; one might be logically prior to another, but in time they are together and priority is excluded. Nevertheless after each distinct representation a, b, c, d there probably follows, as we have supposed, some trace of that movement of attention of which we are aware in passing from one presentation to another. In our present reminiscences we have, it must be allowed, little direct proof of this interposition, though there is strong indirect evidence of it in the tendency of the flow to follow the order in which the presentations were first attended to. With the movements themselves we are familiar enough, though the residua of such movements are not ordinarily conspicuous. These residua, then, are our temporal signs, and, together with the representations connected by them, constitute the memory-continuum. But temporal signs alone will not furnish all the pictorial exactness of the time-perspective. They give us only a Hxed series; but the working of obliviscence, by insuring a progressive variation in intensity and distinctness as we pass from one member of the series to the other, yields the effect which we call time-distance. By themselves such variations would leave us liable to confound more vivid representations in the distance with fainter ones nearer the present, but from this mistake the temporal signs save us; and, as a matter of fact, where the memory-train is imperfect such mistakes continually occur. On the other hand, where these variations are slight and imperceptible, though the memory-1 Cf. W. James, Principles of Psychology, i. 629 sqq.;L.W. Stern, “ Psychische Prasenzzeit, " Z. f. Psych., (1897), xiii. 325 sqq. XXII. IQ
continuum preserves the order of events intact, we have still no such distinct appreciation of comparative distance in time as we have nearer the present where these perspective effects are considerable.
29. When in retrospect we note that a particular presentation X has had a place in the field of consciousness, while certain other presentations, A B C D . . ., have succeeded D ti each other, then we may be said in observing this "ra on relation of the two to perceive the duration of X. And it is in this way that we do subjectively estimate longer periods of time. But first, it is evident that we cannot apply this method to indefinitely short periods without passing beyond the region of distinct presentation; and, since the knowledge of duration implies a relation between distinguishable presentations A B C D and X, the case is one in which the hypothesis of subconsciousness can hardly help any but those who confound the fact of time with the knowledge of it. 'Secondly, if we are to compare different durations at all, it is not enough that one of them should last out a series A B C D, and another a series L M N 0; we also want some sort of common measure of those series. Locke was awake to this point, though he expresses himself vaguely (Essay, ii. I4, §§ 9-12). He speaks of our ideas succeeding each other “ at certain distances not much unlike the images in the inside of a lantern turned round by the heat of a candle, ” and “ guesses ” that “ this appearance of theirs in train varies not very much in a waking man.” Now what is this “ distance” that separates A from B, B from C, and so on, and what means have we of knowing that it is tolerably constant in waking life? It is probably that the residuum of which we have called a temporal sign; or, in other Words, it is the movement of attention from A to B. But We must endeavour here to get a more exact notion of this movement. Everybody knows what it is to be distracted by a rapid succession of varied impressions, and equally what it is to be wearied by the slow and monotonous recurrence of the same impressions. Now these “ feelings ” of distraction and tedium owe their characteristic qualities to movements of attention. In the first, attention is kept incessantly on the move; before it is accommodated to A, it is disturbed by the suddenness, intensity, or novelty of B; in the second, it is kept all but stationary by the repeated presentation of the same impression. Such excess and defect of surprises make one realize a fact which in ordinary life is so obscure as to escape notice. But recent experiments have set this fact in a more striking light, and made clear what Locke had dimly before his mind in talking of a certain distance between the presentations of a waking man. In estimating very short periods of time, of a second or less-indicated say by the beats of a metronome-it is found that there is a certain period for which the mean of a number of estimates is correct, while shorter periods are on the whole over-estimated, and longer periods under-estimated. This we may perhaps take to be evidence of the time occupied in accommodating or fixing attention. Whether the “ point of indifference ” is determined by the rate of usual bodily movement, as Spencer asserts and Wundt conjectures, or conversely, is a question we need not discuss just now. But, though the fixation of attention does of course really occupy time, it is probably not in the first instance perceived as time, i.e. as continuous “ pro tensity, ” to use a term of Hamilton's, but as intensity. Thus, if this supposition be true, there is an element in our concrete time-perception which has no place in our abstract conception' of time. In time conceived as physical there is no trace of intensity; in time psychically experienced duration is primarily an intensive magnitude, witness the comparison of times when we are “ bored ” with others when we are amused. It must have struck every one as strange who has reflected upon it that a period of time which seems long in retrospect-such as an eventful excursion-should have appeared short in passing; while a period, on the contrary, which in memory has dwindled to a wretched span seemed everlasting till it was gone. But, if we consider that in retrospect length of time is represented primarily and chiefly by impressions that have survived, we havelan explanation of one-half; and in the intensity of the movements of attention we shall perhaps ind an explanation II