Page:Popular Science Monthly Volume 28.djvu/369

Rh the special senses, external impulses are conveyed to the brain, light through the optical channel, sounds through the auditory nerve. But at first visible things are not seen nor sounds heard. It is only by numberless repetitions of like sensations that an impression is at length produced. Like sensations are gradually integrated until perceptions arise. As we trace onward the process by which sensations become perceptions and perceptions grow to conceptions, we find that all orders of ideas are built up out of the states of consciousness produced in us by things and their relations. As I wrote, fifteen years ago: We know things because, when we see, hear, touch, or taste them, the present impression spontaneously blends with like impressions before experienced. We know or recognize an external object, not by the single impression it produces, but because that impression revives a whole train or group of previous discriminations that are like or related to it. If something is seen, heard, felt, or tasted, which links itself to no kindred idea, we say, "We do not know it"; if it partially agrees with an idea, or revives a few discriminations, we know something about it, and the completer the agreement the more perfect the knowledge. As to know a thing is to perceive its differences from other things and its likeness to other things, it is strictly an act of classing. This is involved in every act of thought, for to recognize a thing is to class its impression or idea with previous states of feeling. Classification in all its aspects and applications is but the putting together of things that are alike—the grouping of objects by their resemblances; and as to know a thing is to know that it is like this or that, to know what it is like and what it is unlike we begin to classify as soon as we begin to think.

In early infancy, when the mind is first making the acquaintance of outward things, mental growth consists essentially in the production of new ideas by means of repetitions of sense-impressions, and in this process the pre-established relations among the cells and fibers of the brain are of the greatest possible moment. The organized and semi-organized groups of relations among the cerebral elements can give no knowledge until the special groups of relations to which they correspond have been presented to the consciousness by means of the child's daily and hourly experience of objects and activities. The attributes of size, color, weight, transparency, roughness, hardness, fluidity, warmth, taste, and various other properties of solid and liquid substances, and the aspects of people and domestic animals, are noted. Ideas of all the common objects of the house, the grounds, the walks, the drives, are soon formed and associated with words that denote them. Through its spontaneous activity it has hit upon those special co-ordinations of movement required in creeping, walking, holding things, and the like, which have greatly aided in enlarging its knowledge, so that, at the end of a few months, it has a store of complex conceptions, and has acquired numerous aptitudes and dexterities. Hence its early