Page:Popular Science Monthly Volume 43.djvu/519

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503
HOW PLANTS AND ANIMALS GROW.

ence in the same manner as upon a surface of water originally at rest, and by continually uniting with the larger waves they impart those dangerous qualities to the wave which result from high and acuminate crests.

When a film of oil is spread over the surface of the water, this heaping-up action, which in the case of the water film results in the formation of ripples, can not take place. In the figure, let PSM V43 D519 Heaped oil creates increased surface tension to prevent wave formation.jpgFig. 7. A represent the crest of a wave covered by the film of oil B C, and let P be a point of greatest action of the tangential force of the wind, which is supposed to move in the direction of the arrow. The tendency of this action is to drive the film into a heap immediately in front of P. By this action a greater tension is generated in the film at b and a lesser tension at a. The greater tension at b tends to draw the portion at b' ahead, and the lesser tension at a allows the tension at a' to draw the portion at a ahead; so that, instead of a tendency toward heaping up, there is a tendency to move the entire surface film along at a uniform rate. The formation of ripples is therefore stopped, and the growth of waves and the formation of breaking crests, as far as they result from this cause, are prevented.

 

HOW PLANTS AND ANIMALS GROW.
By Dr. MANLY MILES.

TOO little is known in regard to the chemistry of foods, or the specific use made of their proximate constituents in the processes of nutrition, to serve as a rational guide in formulating diets, or estimating the relative nutritive value of different articles of food. Our methods of chemical investigation are not as yet sufficiently delicate and refined to enable us to trace the unobtrusive transformations of matter and energy involved in the nutrition of living beings.

Liebig's chemical theories of nutrition are now discarded by physiologists as fallacious and misleading, but they are, nevertheless, confidently adopted by popular writers on the economy of foods and diets, who are not aware of the progress made in a more consistent knowledge of physiological processes. The history of biological science furnishes numerous instances of error arising from the undue prominence given to non-essential details which are readily observed, while the dominant factors in the phenomena under investigation, which are not so obvious, are overlooked or assigned a subordinate position.