----------+--------------------------------------------------------------- | DAY. +------+------+------+------+------+------+-------+------+------ |First |Second|Third |Fourth|Fifth |Sixth |Seventh|Eighth|Ninth ----------+------+------+------+------+------+------+-------+------+------ |Inches|Inches|Inches|Inches|Inches|Inches|Inches |Inches|Inches Right hand| 28.8 | 33.7 | 35.6 | 36.6 | 40.9 | 44.7 | 47.0 | 48.8 | 48.6 Left hand | 29.6 | .... | .... | .... | .... | .... | .... | .... | 42.3 ----------+------+------+------+------+------+------+-------+------+------ Thus the left hand had gained about fifty per cent in strength through practice of the right hand. This peculiar phenomenon of transference of the effects of practice from one side to the other I have ventured to call "cross-education." The phenomenon was curious enough to suggest other experiments. Another student, Miss T. L. Smith, was set to trying to insert the point of a needle at the end of a rod into a small hole in a drill-gauge without touching the sides. The first experiment consisted of twenty trials with the left hand, with a success of fifty per cent. Immediately thereafter twenty trials were made with the right hand, with a success of sixty per cent. On the following day and on each succeeding day two hundred experiments were made with the right hand, with successes of 61, 64, 65, 75, 74, 75, 82, 79, 78, and 88 per cent. On the last day the left hand, which had not been practiced in the meantime, was again tried, with a success of seventy-six per cent. These last experiments remind us of certain familiar phenomena. It has frequently been noticed that persons taught to write with the right hand become able to write backward, but not forward, with the left hand. This is the so-called "mirror writing," which appears correct if seen in a mirror. The first published observation of this fact exists in a letter from H. F. Weber to Fechner, the founder of experimental psychology. Fechner, moreover, noticed that with the left hand he could make the figure 9 backward better than in the regular way. Curiously enough, the principle of cross-education has been put to practical use. A letter (with permission to publish) has been received from Oscar Raif, Professor of Music in the Berlin Hochschule: