330 LAUGEL'S PROBLEMS OF NATURE AND LIFE. 



in their most general sense, are at once the exponents 

 and instruments. To this atomic theory we shall ha,ve 

 occasion to allude again. Meanwhile we must treat of 

 it here as practically the foundation of modern che- 

 mistry, of its researches, doctrines, and nomenclature. 

 Iii its origin a rude and unformed bequest of ancient 

 philosophy, it is now fashioned and perfected into a 

 system to which the attributes of number, weight, and 

 proportion give a character of proof next to mathe- 

 matical in kind. The power of predicting results, and 

 obtaining them after prediction, is the high prerogative 

 of the chemist of our day. He may feel justly proud 

 of those tables which, in the synthetical exactness of 

 their series, even when most complex, express at once 

 the certainty of the facts and the subtlety of the pro- 

 cesses by which they were obtained. The gaps in 

 these series have been gradually filled up, in accord- 

 ance with the laws of numerical proportion, which 

 determine the relations of atoms in their simplest form. 

 The secondary relations of compound atoms, or mole- 

 cules, as they are distinctively called, show the same 

 fixity of combination according to atomic weights ; 

 even the most complex union of compound bodies ever 

 taking place in multiples of the combining proportions. 

 The curious facts regarding chemical equivalents, or 

 the substitution of one elementary body for another in 

 a given compound, all attest the same law of definite 

 proportions ; which, even apart from experiment, might 

 be presumed a necessary consequence and corollary to 

 the atomic theory. Securely aided by this theory, the 

 chemist penetrates deeply into the intimate constitu- 



