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 
erystals 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 tke law of 
definite proportions, and compose chemical species, are made 
