vii LAW AND PRINCIPLE 177 



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no exception has been found, is the law of the conserva- 

 tion of energy, which asserts that though energy can be 

 converted from one form to another it cannot be created 

 or destroyed. A related generalisation of much greater 

 antiquity is the law of the conservation of matter, upon 

 the foundation of which modern chemistry has been 

 built. Whenever a chemical change takes place, whether 

 in the burning of a candle, the explosion of gunpowder, 

 or in any other form, the weight of the substances 

 produced is equal to the sum of the weights of the 

 constituents involved in the change. Since Lavoisier 

 enunciated this principle, the most accurate investiga- 

 tions have failed to detect a loss or gain of the minutest 

 particle of matter; and the permanence of the amount of 

 material in our universe is, therefore, an axiom of science. 

 The Sicilian philosopher, Empedocles, born about 

 494 B.C., seems to have been the first to associate changes 

 of matter into various forms with force or energy. He 

 regarded fire and earth and air and water as the four 

 " elements," and said they were influenced by two 

 dynamic powers or principles Love and Strife one 

 tending to bring them together and the other to separate 

 them. In his universe there was no creation or absolute 

 destruction of the " elements," but only changing 

 combinations and transformations. " For," he said, 

 " from what does not exist at all it is impossible that 

 anything can come into being, and it is neither pos- 

 sible nor percejvable that being should perish com- 

 pletely." By considering the four material " elements " 

 as eternal but changing in composition through the 

 action of forces of attraction and repulsion, Empedocles 

 approached nearer than any other early philosopher to 

 the modern doctrines of the conservation of matter and 



the relation between matter and energy, 

 u. D. M 



