72 FRAGMENTS OF SCIENCE. 



but this work is at bottom the molecular work of the 

 transmuted food and the oxygen of the air. We inhale 

 this vital gas, and bring it into sufficiently close prox- 

 imity with the carbon and the hydrogen of the body. 

 These unite in obedience to their mutual attractions; 

 and their motion towards each other, properly turned 

 to account by the wonderful mechanism of the body, 

 becomes muscular motion. 



One fundamental thought pervades all these state- 

 ments: there is one tap root from which they all 

 spring. This is the ancient maxim that out of nothing 

 nothing comes; that neither in the organic world nor 

 in the inorganic is power produced without the ex- 

 penditure of power; that neither in the plant nor in 

 the animal is there a creation of force or motion. Trees 

 grow, and so do men and horses; and here we have new 

 power incessantly introduced upon the earth. But its 

 source, as I have already stated, is the sun. It is the 

 sun that separates the carbon from the oxygen of the 

 carbonic acid, and thus enables them to recombine. 

 Whether they recombine in the furnace of the steam- 

 engine or in the animal body, the origin of the power 

 they produce is the same. In this sense we are all 

 * souls of fire and children of the sun.' But, as re- 

 marked by Helmholtz, we must be content to share 

 our celestial pedigree with the meanest of living things. 



Some estimable persons, here present, very possibly 

 shrink from accepting these statements; they may be 

 frightened by their apparent tendency towards what is 

 called materialism a word which, to many minds, ex- 

 presses something very dreadful. But it ought to be 

 known and avowed that the physical philosopher, as 

 such, must be a pure materialist. His enquiries deal 

 with matter and force, and Avith them alone. And 

 whatever be the forms which matter and force assume, 



