112 THE POPULAR SCIENCE MONTHLY. 



serve in this condition a new evidence of the depreciation of the 

 caiDacity of the yonnger pnpils 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" ad- 

 verse 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 sci- 

 ence 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 devel- 

 oped in all respects, then his understanding also will unfold rap- 

 idly and attain full maturity under continuous natural direction 

 and instruction ; all the more vigorous will his physical develop- 

 ment 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 hiin 

 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 youth- 

 ful 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." 



It is shown by M. Camena <T 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. 



