The observer then thinks he sees in broad light a letter which is not there, if that letter, in virtue of the general sense, ought to appear in the phrase. But you can go further, and vary the experiment. Suppose we write the word "tumult" correctly. After doing so, to direct the memory of the observer into a certain trend of recollection, call out in his ear, during the short time the light is turned on, another word of different meaning, for example, the word "railway." The observer will read "tunnel"; that is to say, a word, the graphical outline of which is like that of the written word, but connected in sense with the order of recollection called up. In this mistake in reading, as in the spontaneous correction of the previous experiment, we see very clearly that perception is always the fulfilment of guesswork. It is the direction of this work that we are concerned to determine. According to the popular idea, perception has a completely speculative interest: it is pure knowledge. Therein lies the fundamental mistake. Notice first of all how much more probable it is, a priori, that the work of perception, just as any other natural and spontaneous work, should have a utilitarian signification. "Life," says Mr Bergson with justice, "is the acceptance from objects of nothing but the useful impression, with the response of the appropriate reactions." ("Laughter", page 154.) And this view receives striking objective confirmation if, with the author of "Matter and Memory", we follow the progress of the perceptive functions along the animal series from the protoplasm to the higher vertebrates; or if, with him, we analyse the task of the body, and discover that the nervous system is manifested in its very structure as, before all, an instrument of action. Have we not already besides proof of this in the fact that each of us always appears in his own eyes to occupy the centre of the world he perceives? The "Riquet" of Anatole France voices Mr Bergson's view: "I am always in the centre of everything, and men and beasts and things, for or against me, range themselves around." But direct analysis leads us still more plainly to the same conclusion. Let us take the perception of bodies. It is easy to show--and I regret that I cannot here reproduce Mr Bergson's masterly demonstration--that the division of matter into distinct objects with sharp outlines is produced by a selection of images which is completely relative to our practical needs.