486 FKAGMENTS OF SCIENCE. 



come their heat, and the work producible by that heat ? 

 From the immeasurable 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 living, 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 whereby the wave-motion of 

 the sun is changed into the rigid form of chemical ten- 

 sion, and thus prepared for future use. With this pre- 

 vision, as shall subsequently be shown, the existence 

 of the human race itself is inseparably connected. 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, 

 and the amount of power thus sacrificed is accurately 

 restored by the combustion of the tree. The heat and 

 work potential in our coal strata are so much strength 

 withdrawn from the sun of former ages. Mayer lays the 

 axe to the root of the notions regarding ' vital force ' 

 which were prevalent when he wrote. With the plain 

 fact before us that in the absence of the solar rays 

 plants cannot perform the work of reduction, or generate 

 chemical tensions, it is, he contends, incredible that these 

 tensions should be caused by the mystic play of the vital 

 force. Such an hypothesis would cut off all investiga- 

 tion ; it would land us in a chaos of unbridled phantasy. 



