216 THE KIDDLE OF THE UNIVERSE. 



proceed to furnish the proof of it. But we must first 

 devote a few words to each of the two laws. 



The law of the "persistence " or " indestructibility of 

 matter," established by Lavoisier in 1789, may be 

 formulated thus : The sum of matter, which fills 

 infinite space, is unchangeable. A body has merely 

 changed its form, when it seems to have disappeared. 

 When coal burns, it is changed into carbonic acid gas 

 by combination with the oxygen of the atmosphere ; 

 when a piece of sugar melts in water, it merely passes 

 from the solid to the fluid condition. In the same 

 way, it is merely a question of change of form in the 

 cases where a new body seems to be produced. A 

 shower of rain is the moisture of the atmosphere cast 

 down in the form of drops of water ; when a piece of 

 iron rusts, the surface layer of the metal has combined 

 with water and with atmospheric oxygen, and formed 

 a " rust," or oxy-hydrate of iron. Nowhere in nature 

 do we find an example of the production, or " crea- 

 tion," of new matter ; nowhere does a particle of 

 existing matter pass entirely away. This empirical 

 truth is now the unquestionable foundation of 

 chemistry ; it may be directly verified at any 

 moment by means of the balance. To the great 

 French chemist Lavoisier belongs the high merit of 

 first making this experiment with the balance. At 

 the present day the scientist, who is occupied from 

 one end of the year to the other with the study of 

 natural phenomena, is so firmly convinced of the 

 absolute "constancy" of matter that he is no longer 

 able to imagine the contrary state of things. 



We may formulate the "law of the persistence of 

 force " or " conservation of energy " thus : The sum 

 of force, which is at work in infinite space and 



