4 BIOLOGY. [Book i. 



destined evermore to pass from one edifice to another. Their 

 totality constitutes the general substance of the universe, and, 

 in reality, this general substance undergoes no other changes 

 than modifications in the distribution of its constituent ele- 

 ments. All the phenomena, all the varied aspects, all the 

 revolutions of the universe can be referred essentially to simple 

 atomic displacements. 



This grand theory, so admirably simple and seductive, would 

 be nothing but a brilliant speculation, if facts, numerous and 

 rigorously observed, did not now serve it as basis and demon- 

 stration. 



We rapidly enumerate the most important of these facts, which 

 belong for the most part to the domain of Physics and Chemistry. 

 Wenzel, Eichter, Proust proved fii'st of all that in chemical 

 compositions and decompositions, bodies combine according to 

 proportions rigorously defined. Dalton formulated the law of 

 multiple proportions, and deduced therefrom naturally that 

 matter is constituted by atoms extended, having a constant 

 weight, and that those atoms are of various species. 



When atoms of the same species come into juxtaposition, we 

 have what we call simple bodies, such as hydrogen, oxygen, 

 azote. On the contrary, the bodies called compound result from 

 the juxtaposition of atoms of diversified nature, whence come 

 acids, salts, oxides, and also all the unstable and complex 

 compounds which constitute organic substances. 



This is not all : to the law of Dalton the law of Avogadro 

 and of Ampfere is adjoined. This last law establishes that all 

 gases, temperature and pressure being equal, have the same 

 elastic force. But as this force is probably due to the shock 

 of atoms or groups of atoms, molecules, on the sides of the 

 vessels which imprison the gases, we must admit that in the 

 conditions aforesaid all gases contain, under the same volume, 

 the same number of molecules or of atoms. 



Finally, Dulong and Petit have been able to show, experi- 

 mentally, that the atoms of simple bodies all possess the same 

 specific heat. 



