Page:Popular Science Monthly Volume 38.djvu/122

112 in this condition a new evidence of the depreciation of the capacity of the younger pupils of these classes to resist unhealthy influences.

It is incumbent on us to see with all possible care that the growth of youth during their years of puberty, which is so full of importance, is not disturbed or distorted by any influences adverse to nature. But as instruction is now arranged, at school and at home, we should first of all direct attention to the phase of the child's age immediately preceding the period of puberty, when the growth is at its lowest, the child's capacity for resistance is least, and his liability to illness increases from year to year. We must learn how to obviate this liability to illness, and it is for science to forge the weapons with which to do it.

The deeper we go into these researches, the more we appreciate the great truth that lies in the conception expressed by Rousseau in the last century. When, he thought, we have brought a boy to the age of puberty with a body sound, healthy, and well developed in all respects, then his understanding also will unfold rapidly and attain full maturity under continuous natural direction and instruction; all the more vigorous will his physical development be afterward in the bloom of youth. Rousseau, we know, would not recognize a compulsory lesson in a book before the twelfth year as a means of instruction. We can not follow him so far, but we certainly shall have to learn, better than we know now, how to fit our demands on the child's organization to his strength and capacity of resistance during the different periods of his growth; better than we know now, how to promote his health and his vigorous physical development. The father of school hygiene, Johann Peter Frank, introduced his warning a hundred years ago against a too early and too strong tension of the youthful powers of mind and body with the words: "Yet spare their fibers—spare their mind's strength; waste not upon the child the vigor of the man that is to be."

is shown by M. Camena d'Almeida, from a comparison of mountain-heights as giver) in Berghause's table, that the altitude of the highest masses increases in going from the polar to the equatorial regions; yet the greatest elevations are not found at the equator, but near the tropics in 27° 59' and 35° 28' north in Asia, and 15° 52' and 19° 47' south in South America. These points are also near the isothermal lines of the highest summer temperatures. The heights of the mountains seem, too, to bear a relation to the height of the line of perpetual snow, they seldom rising more than from six thousand to ten thousand feet above it. From these facts the author deduces a relation between the height of mountains and climate; assuming that there is a limit above the snow-line above which, if a mountain passes it, it is so ground down by frost and the wear of the elements as speedily to be reduced to a proper level.