dependence of the other, both about the same time, and both carried energetically to the goal. In many other cases in which either right or left hand is given in the tables, the other hand also moves, but in a subordinate and aimless way. There was a very marked difference between the use of both hands in some cases, and of one hand followed by, or accompanied by, the other in other cases. It was very rare that the second hand did not thus follow or accompany the first; and this was extremely marked in the violent reaching for which the right hand was mainly used. This hand was almost invariably accompanied by an objectless and fruitless symmetrical movement of the other.
The results of the entire series of experiments on the use of the hands may be stated as follows, mainly in the words in which I reported them summarily some time ago:[1]
1. I found no trace of preference for either hand as long as there were no violent muscular exertions made (based on 2,187 systematic experiments in cases of free movement of hands near the body: i. e., right hand, 577 cases; left hand, 568 cases; a difference of nine cases; both hands, 1,043 cases; the difference of nine cases being too slight to have meaning).
2. Under the same conditions the tendency to use both hands together was about double the tendency to use either (seen from the number of cases of the use of both hands in the statistics given above), the period covered being from the child's sixth to her tenth month inclusive.
3. A distinct preference for the right hand in violent efforts in reaching became noticeable in the seventh and eighth months. Experiments during the eighth month on this cue gave, in 80 cases, right hand, 74 cases; left hand, 5 cases; both hands, 1 case. This was true in two very distinct classes of cases: first, reaching for neutral objects (newspaper, etc.) at more than the reaching distance; and, second, reaching for bright colors at any distance. Under the stimulus of bright colors, from 86 cases, 84 were right-hand cases and 2 left-hand. Right-handedness had accordingly developed under pressure of muscular effort in the sixth and seventh months.
4. Up to this time the child had not learned to stand or to creep; hence the development of one hand more than the other is not due to differences in weight between the two longitudinal
- ↑ Science, xvi, October 31, 1890; discussed by James, Science, November 8, 1890, by Dr. J. T. O'Connor, ibid., xvi, 1890, p. 331, and by myself, ibid., xvi, November 28, 1890. The report is quoted in full in Nature, November 13, 1890, and in part in the Illustrated London News, January 17, 1891. See also Ebbinhaus's Zeitsch. für Psychologie, ii, 1891, p. 239; Wilson, The Eight Hand: Left-handedness, pp. 128-131; Revue Scientifique, 1891, ii, p. 493; discussed by Mazel, Revue Scientifique, 1892, i, p. 113. Both writers in the last named journal cite these experiments wrongly as Wilson's.
