Page:Popular Science Monthly Volume 30.djvu/461

Rh is an express order from the ideational centers after this deliberation has been gone through.

In habitual action, on the contrary, the only impulse which the centers of idea or perception need send down, is the initial impulse, the command to start. This is represented in the diagram by V; it may be a thought of the first movement or of the last result, or a mere perception of some of the habitual conditions of the chain, the presence, e.g., of the key-board near the hand. In the present case, no sooner has the conscious thought or volition instigated movement A, than A, through the sensation a, of its own occurrence awakens B reflexly; B then excites C through b, and so on till the chain is ended, when the intellect generally takes cognizance of the final result. The process, in fact, resembles the passage of a wave of "peristaltic" motion down the bowels. The intellectual perception at the end is indicated in the diagram by the effect of G being represented, at G', in the ideational centers above the merely sensational line. The sensational impressions, a, h, c, d, e, f, are all supposed to have their seat below the ideational lines. That our ideational centers, if involved at all by a, b, c, d, e, f, are involved in a minimal degree, is shown by the fact that the attention may be wholly absorbed elsewhere. We may say our prayers, or repeat the alphabet, with our attention far away.

"A musical performer will play a piece which has become familiar by repetition, while carrying on an animated conversation, or while continuously engrossed by some train of deeply interesting thought; the accustomed sequence of movements being directly prompted by the sight of the notes, or by the remembered succession of the sounds (if the piece is played from memory), aided in both cases by the guiding sensations derived from the muscles themselves. But, further, a higher degree of the same 'training' (acting on an organism specially fitted to profit by it) enables an accomplished pianist to play a difficult piece of music at sight; the movements of the hands and fingers following so immediately upon the sight of the notes, that it seems impossible to believe that any but the very shortest and most direct track can be the channel of the nervous communication through which they are called forth. The following curious example of the same class of acquired aptitudes, which differ from instincts only in being prompted to action by the will, is furnished by Robert Houdin:

"With a view of cultivating the rapidity of visual and tactile perception, and the precision of respondent movements, which are necessary for success in every kind of prestidigitation, Houdin early practiced the art of juggling with balls in the air; and having, after a month's practice, become thorough master of the art of keeping up four balls at once, he placed a book before him, and, while the balls were in the air, accustomed himself to read without hesitation. 'This,' he says, 'will probably seem to my readers very extraordinary; but I shall surprise them still more when I say that I have just amused