hand in squeezing a dynamometer develops the strength of the other members of the body, will it not also develop their dexterity or their advance? Again, if the development of voluntary power—let us say, frankly, "will power"—in one direction brings about a development in other directions, why should we limit the transference to muscular activity? Why can we not expect that the development should be extended to the higher forms of will power that go to make up character? The outlook begins to be stirring on account of its vastness. If the last principle be admitted, there seems no argument against the claim that some forms of manual training, such as lathe work and forge work, are just the things to develop moral character. By the same reasoning we would be obliged to admit the often-made argument that training in Latin, Greek, and mathematics furnishes a means of general mental development. If we admit the principle, we find ourselves at once involved in important educational controversies. However we may think in respect to these questions, it is plain that it is worth while to climb a ladder which has such an outlook at the top. Let us begin.
In the first place, the fact of cross-education is established. Let us ask in what this education consists. On this point some curious observations have been made by Prof. W. W. Davis,[1] now of Iowa College. The subject of the experiment began by raising a five-pound dumb-bell by flexing the arm at the elbow; this called into play chiefly the biceps muscle for lifting and the forearm muscles for grasping. This was done as many times as possible with the right arm, and then, after a rest, with the left arm. The subject then entered upon a practice extending from two to four weeks; this consisted in lifting the weight with the right arm only. At the end both arms were tested as at the start.
The results were strange enough. The unpracticed left arm gained in power as we expected, but it also gained in size. Careful measurements were made by Dr. J. W. Seaver, of the Yale Gymnasium, on the girths of both upper arm and forearm. Let us compare the gains in girth with the gains in power:
| Subject. | GAINS IN GIRTH. | GAINS IN POWER. | ||
| Right biceps. | Left biceps. | Right arm. | Left arm. | |
| G | 5 mm | —5 mm | 820 flexions | 200 flexions |
| J | 2" | 0" | 400" | 225" |
| K | 4" | 2" | 724" | 514" |
| H | 13" | 6" | 950" | 30" |
| B | 6" | 11" | 900" | 75" |
| I | 8" | 3" | 750" | 75" |
- ↑ Studies from the Yale Psychological Laboratory, vol. vi.
