We must not, however, attempt to divert it from these channels by damming it up, but by opening other channels that will draw it away in better directions.
2.

In encouraging the activity of children, and in guiding the direction of it in their hours of play, we must not expect to make it available for useful results, other than that of promoting their own physical development and health.

At least, we can do this only in a very limited degree.

Almost all useful results require for their attainment a long continuance of efforts of the same kind--that is, expenditure of the vital force by the continued action of the same organs.

Now, it is a principle of nature that while the organs of an animal system are in process of formation and growth, they can exercise their power only for a very brief period at a time without exhaustion.