Page:Popular Science Monthly Volume 49.djvu/652

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where they may bring with them some special addition to our stock of arts or articles of culture. (Works, ii, p. 576.)

Neither Madison nor any of the others had any conception of modern immigration, and apparently never realized that their moderate and, as they supposed, well-regulated encouragement would bring it about.



I HAVE already had occasion more than once to speak of the development of a mental state from the stage which we term idea to that which we term sensation. Before taking up the matter in hand it will be necessary to go into this question at somewhat greater length.

We seldom have difficulty in discriminating an idea from a sensation, but it is not easy to define the difference between them. This is partly due to the fact that the differences are very complex, and partly to the fact that they vary in the respective fields of sensation, so that one can scarcely frame a definition for ideas and sensations of vision that will also prove applicable to those of sound, touch, and so on. Ideas of sound differ from the corresponding sensations chiefly in intensity, but in the case of vision a much more important distinction is drawn from the relation sustained by visual ideas to what the eye actually sees. At the present moment I am thinking of something I saw yesterday, but what I see with my eyes is not in the least affected by that. The two groups remain distinct, and it would seem as if an almost impassable gulf parted them, so seldom does a bit of one become confused with the other. This is not true of ideas of sound. If they only become intense enough they may seem to blend with real sounds—indeed, I often mistake an air of which I am thinking for the same air faintly heard.

The distinction between sense-impression and idea really rests upon intrinsic differences of this kind, but as they are so complex I shall make use of a physiological distinction which for all practical purposes coincides with it. Sense-impressions are those mental states which are primarily initiated by a current from the outlying regions or periphery of the body, especially from the organs of sense. Since these currents are usually due to the action of physical forces upon the body, sense-impressions generally give us information as to the condition of the material world. All other mental states should be classed as ideas, even though they simulate sensations so closely as to be scarcely distinguishable from them.