THE CHEMICAL AND NATURAL SCIENCES 207 



foundations of the atomic theory. Bodies are composed 

 of material atoms which differ from one another only in 

 magnitude, shape and weight. These atoms by com- 

 bining and separating produce all sensible phenomena. 

 Up to a certain point Plato combines the ideas of 

 Empedocles with those of Democritus. According to 

 him, mathematical facts constitute the intelligible 

 basis of the world which the Demiurge desired to 

 create ; but in order that this world might become 

 tangible and visible, it had to be brought into existence 

 under the form of earth and fire. Moreover, as earth 

 and fire cannot enter into direct relationship with one 

 another, it was necessary to unite them by means of 

 water and air in the following proportions : x 



fire air water 

 air water earth 



In order that combinations may be formed between 

 these constituent elements of the universe, it is neces- 

 sary that these should take the form of regular poly- 

 hedra ; therefore the earth-element will be a cube, the 

 water-element an octahedron, the air-element an 

 icosahedron, and the fire-element a tetrahedron. 

 From the fact that there exists a fifth regular poly- 

 hedron, the dodecahedron (the faces of which are 

 pentagonal) Plato deduced the existence of a fifth 

 element also, namely, the ether. The ideas of Plato 

 and particularly of Democritus resemble in many 

 respects the conceptions of modern chemistry. They 

 had, however, but slight influence on the development 

 of the science because they evaded the methods of 

 experimental verification which were in use until the 

 end of the eighteenth century. 



In this domain also, the conceptions of Aristotle, 

 afterwards seen to be false, had an important influence. 

 Aristotle begins by opposing matter and form. The 

 1 13 Duhem, Systime, I, p. 30 et seq. 



