foresees a future phenomenon, it is only on condition of making it to a certain extent a present phenomenon, or at least of enormously reducing the interval which separates us from it. In short, the time of which we speak in astronomy is a number, and the nature of the units of this number cannot be specified in our calculations; we may therefore assume them to be as small as we please, provided that the same hypothesis is extended to the whole series of operations, and that the successive relations of position in space are thus preserved. We shall then be present in imagination at the phenomenon we wish to foretell; we shall know exactly at what point in space and after how many units of time this phenomenon takes place; if we then restore to these units their psychical nature, we shall thrust the event again into the future and say that we have foreseen it, when in reality we have seen it. [Sidenote: In dealing with states of consciousness we cannot vary their duration without altering their nature.] But these units of time which make up living duration, and which the astronomer can dispose of as he pleases because they give no handle to science, are just what concern the psychologist, for psychology deals with the intervals themselves and not with their extremities. Certainly pure consciousness does not perceive time as a sum of units of duration: left to itself, it has no means and even no reason to measure time; but a feeling which lasted only half the number of days, for example, would no longer be the same feeling for it; it would lack thousands of impressions which gradually thickened its substance and altered its colour. True, when we give this feeling a certain name, when we treat it as a thing, we believe that we can diminish its duration by half, for example, and also halve the duration of all the rest of our history: it seems that it would still be the same life, only on a reduced scale. But we forget that states of consciousness are processes, and not things; that if we denote them each by a single word, it is for the convenience of language; that they are alive and therefore constantly changing; that, in consequence, it is impossible to cut off a moment from them without making them poorer by the loss of some impression, and thus altering their quality. I quite understand that the orbit of a planet might be perceived all at once or in a very short time, because its successive positions or the _results_ of its movement are the only things that matter, and not the duration of the equal intervals which separate them. But when we have to do with a feeling, it has no precise result except its having been felt; and, to estimate this result adequately, it would be necessary to have gone through all the phases of the feeling itself and to have taken up the same duration. Even if this feeling has finally issued in some definite action, which might be compared to the definite position of