THE COPLEY MEDALIST OF 1871. 433 



Having thus, with firm step, passed through the 

 powers of inorganic nature, his next object is to bring 

 his principles 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 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 organ- 

 isms which, while living, take in the solar light, and 

 by its consumption generate forces of another kind. 

 These organisms are plants. The vegetable world, in- 

 deed, constitutes the instrument whereby 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 

 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 sunlight/ 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 strata are so much strength withdrawn from the sun of 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 



