18 NATURE AND LIFE. 



cal, just as the two sorts of phosphorus are. These cases 

 of isomery, which are quite numerous, attest with the 

 strongest evidence the excessive variability of which com- 

 binations of force are capable. When we see the same 

 elements, combined in the same weight-proportions, pro- 

 duce sometimes harmless substances, sometimes terrible 

 poisons, in one case evolve colorless or dingy products, in 

 another brilliant hues, we become convinced that primal 

 matter is of little consequence in comparison with the 

 power of the weaver who arranges its threads, and knows 

 beforehand what the aspect of the web will be. Besides, 

 it is not alone in the whole that the formative principle is 

 displayed ; it shows forth also in the elements, considered 

 individually, since every one of them exhibits tendencies, 

 elective affinities, that bear witness to some obscure instinct 

 toward harmonious completion. 



There is not only a prodigious variety in the disposition 

 of the atoms which make up molecules, and in the arrange- 

 ment of the molecules among themselves, but this arrange- 

 ment is governed, besides, by admirable geometric laws. 

 The atoms that make up molecules are not heaped and 

 flung together at random and in disorder ; they enter into 

 composition only in fixed proportions and in fixed direc- 

 tions. Marc-Antoine Gaudin has proved, in a late treatise 

 devoted entirely to these refined inquiries, the existence of 

 some of the most important laws in the geometry of atoms. 

 This ingenious and persevering writer demonstrates that 

 all chemical molecules, whether they are fitted to produce 

 crystals or not, are formed by a symmetrical aggregation of 

 atoms. The latter are arranged in equilibrium in two direc- 

 tions, perpendicular to each other, one parallel to the axis 

 of grouping, and the other at right angles to that axis, so as 

 always to compose a symmetrical figure. The most compli- 

 cated bodies, so soon as they are brought under the law of 

 definite proportions, and compose chemical species, are made 



