As adult thinkers we have a definite and apparently instantaneous knowledge of the sizes, shapes, and distances of the things amongst which we live and move; and we have moreover a practically definite notion of the whole great infinite continuum of real space in which the world swings and in which all these things are located. Nevertheless it seems obvious that the baby's world is vague and confused in all these respects. How does our definite knowledge of space grow up? This is one of the quarrelsome problems in psychology. This chapter must be so brief that there will be no room for the polemic and historic aspects of the subject, and I will state simply and dogmatically the conclusions which seem most plausible to me. =The quality of voluminousness= exists in all sensations, just as intensity does. We call the reverberations of a thunder-storm more voluminous than the squeaking of a slate-pencil; the entrance into a warm bath gives our skin a more massive feeling than the prick of a pin; a little neuralgic pain, fine as a cobweb, in the face, seems less extensive than the heavy soreness of a boil or the vast discomfort of a colic or a lumbago; and a solitary star looks smaller than the noonday sky. Muscular sensations and semicircular-canal sensations have volume. Smells and tastes are not without it; and sensations from our inward organs have it in a marked degree. Repletion and emptiness, suffocation, palpitation, headache, are examples of this, and certainly not less spatial is the consciousness we have of our general bodily condition in nausea, fever, heavy drowsiness, and fatigue. Our entire cubic content seems then sensibly manifest to us as such, and feels much larger than any local pulsation, pressure, or discomfort. Skin and retina are, however, the organs in which the space-element plays the most active part. Not only does the maximal vastness yielded by the retina surpass that yielded by any other organ, but the intricacy with which our attention can subdivide this vastness and perceive it to be composed of lesser portions simultaneously coexisting alongside of each other is without a parallel elsewhere. The ear gives a greater vastness than the skin, but is considerably less able to subdivide it. The _vastness, moreover, is as great in one direction as in another_. Its dimensions are so vague that in it there is no question as yet of surface as opposed to depth; 'volume' being the best short name for the sensation in question.