=Sensations distinguished from Images.=--Both sensation and perception, for all their difference, are yet alike in that their objects appear _vivid_, _lively_, and _present_. Objects merely _thought of_, _recollected_, or _imagined_, on the contrary, are relatively faint and devoid of this pungency, or tang, this quality of _real presence_ which the objects of sensation possess. Now the cortical brain-processes to which sensations are attached are due to incoming currents from the periphery of the body--an external object must excite the eye, ear, etc., before the sensation comes. Those cortical processes, on the other hand, to which mere ideas or images are attached are due in all probability to currents from other convolutions. It would seem, then, that the currents from the periphery normally awaken a kind of brain-activity which the currents from other convolutions are inadequate to arouse. To this sort of activity--a profounder degree of disintegration, perhaps--the quality of vividness, presence, or reality in the object of the resultant consciousness seems correlated. =The Exteriority of Objects of Sensation.=--Every thing or quality felt is felt in outer space. It is impossible to conceive a brightness or a color otherwise than as extended and outside of the body. Sounds also appear in space. Contacts are against the body's surface; and pains always occupy some organ. An opinion which has had much currency in psychology is that sensible qualities are first apprehended as _in the mind itself_, and then 'projected' from it, or 'extradited,' by a secondary intellectual or super-sensational mental act. There is no ground whatever for this opinion. The only facts which even seem to make for it can be much better explained in another way, as we shall see later on. The very first sensation which an infant gets _is_ for him the outer universe. And the universe which he comes to know in later life is nothing but an amplification of that first simple germ which, by accretion on the one hand and intussusception on the other, has grown so big and complex and articulate that its first estate is unrememberable. In his dumb awakening to the consciousness of _something there_, a mere _this_ as yet (or something for which even the term _this_ would perhaps be too discriminative, and the intellectual acknowledgment of which would be better expressed by the bare interjection 'lo!'), the infant encounters an object in which (though it be given in a pure sensation) all the 'categories of the understanding' are contained. _It has externality, objectivity, unity, substantiality, causality, in the full sense in which any later object or system of objects has these things._ Here the young knower meets and greets his world; and the miracle of knowledge bursts forth, as Voltaire says, as much in the infant's lowest sensation as in the highest achievement of a Newton's brain.