Page:Popular Science Monthly Volume 41.djvu/658

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THE POPULAR SCIENCE MONTHLY.

in one hand and the pencil in the other; in this way the pencil and the plate sway alike, and no record of it is made. The very fine movements thus obtained are shown in Fig. 4; this figure also shows the slight difference between a record taken by this method while the subject is sitting and while standing, which further proves that the swaying of the body has been eliminated. Traces of periodic oscillations are noted in Fig. 4; these are due to respiration movements, and in II, of Fig. 5, they are unusually distinct and regular, about twenty to the minute. The forearm of the hand holding the record-plate rests against the body while the recording hand is held free from it, and thus the abdominal movements are recorded. The movements toward the object of attention appear

PSM V41 D658 Metronome counter trace of 20 seconds.jpg
Fig. 9.— Counting Metronome. Record vertical. Facing . Time, 20 seconds. Pencil held in extended right hand.

throughout. Fig. 5 figures a movement toward the rear as well as toward the front; while Fig. 6 presents a most beautifully regular movement in all four directions. As the metronome, the strokes of which the subject is counting, is carried from one corner of the room to the next, the hand involuntarily follows it and records an almost perfect square.

It is further interesting to record the movements of the two hands during the same experiment; a correspondence of movement would be attributed to a common swaying of the body, but this would not exclude symmetrical movements of the hands as well. Fig. 7 illustrates the close similarity of the movements: while Fig. 8 shows the importance of the position of the arms in such an experiment. The hand that is held away from the body moves more extensively; the form of the movement remains similar. All the above records (and Figs. 9, 10, and 14) were obtained upon the same subject; they are therefore comparable with one another, and illustrate the analysis of the resulting movements into their several factors.

Involuntary movements are not limited to the horizontal plane; we may record vertical movements by holding the record-