456 FRAGMENTS OF SCIENCE 



that the heat developed by friction in the wheels of our 

 wind and water mills comes from the sun in the form of 

 vibratory motion; while the heat produced by mills driven 

 by tidal action is generated at the expense of the earth's 

 axial rotation. 



Having thus, with firm step, passed through the powers 

 of inorganic nature, his next object is to bring his princi- 

 ples to bear upon the phenomena of vegetable and animal 

 life. Wood and coal can burn; whence come their heat, 

 and the work producible by that heat? From the im- 

 measurable reservoir of the sun. Nature has proposed to 

 herself the task of storing up the light which streams 

 earthward from the sun, and of casting into a permanent 

 form the most fugitive of all powers. To this end she 

 has overspread the earth with organisms which, while liv- 

 ing, take in the solar light, and by its consumption generate 

 forces of another kind. These organisms are plants. The 

 vegetable world, indeed, constitutes the instrument where- 

 by the wave-motion of the sun is changed into the rigid 

 form of chemical tension, and thus prepared for future use. 

 With this prevision, as shall subsequently be shown, the 

 existence of the human race itself is inseparably con- 

 nected. It is to be observed that Mayer's utterances are 

 far from being anticipated by vague statements regarding 

 the "stimulus" of light, or regarding coal as "bottled sun- 

 light." He first saw the full meaning of De Saussure's 

 observation as to the reducing power of the solar rays, 

 and gave that observation its proper place in the doctrine 

 of conservation. In the leaves of a tree, the carbon and 

 oxygen of carbonic acid, and the hydrogen and oxygen of 

 water, are forced asunder at the expense of the sun f and 

 the amount of power thus sacrificed is accurately restored 



