ATOMS, MOLECULES, AND ETHEE WAVES. 79 



never been relinquished, and in our own day it is grow- 

 ing steadily in power and precision. 



The union of bodies in fixed and multiple propor- 

 tions constitutes the basis of modern atomic theory. 

 The same compound retains, for ever, the same elements, 

 in an unalterable ratio. We cannot produce pure 

 water containing one part, by weight, of hydrogen and 

 nine of oxygen ; nor can we produce it when the ratio 

 is one to ten ; but we can produce it from the ratio of 

 one to eight, and from no other. So, also, when water 

 is decomposed by the electric current, the proportion, 

 as regards volumes, is as fixed as in the case of weights. 

 Two volumes of hydrogen and one of oxygen invariably 

 go to the formation of water. Number and harmony, 

 as in the Pythagorean system, are everywhere dominant 

 in this under-world. 



Following the discovery of fixed proportions we 

 have that of multiple proportions. For the same com- 

 pound, as above stated, the elementary factors are con- 

 stant ; but one elementary body often unites with 

 another so as to form different compounds. Water, 

 for example, is an oxide of hydrogen ; but a peroxide 

 of that substance also exists, containing exactly double 

 the quantity of oxygen. Nitrogen also unites with 

 oxygen in various ratios, but not in all. The union 

 takes place, not gradually and uniformly, but by steps, 

 a definite weight of matter being added at each step. 

 The larger combining quantities of oxygen are thus 

 multiples of the smaller ones. It is the same with 

 other combinations. 



We remain thus far in the region of fact : why not 

 rest there ? It might as well be asked why we do not, 

 like our poor relations of the woods and forests, rest 

 content with the facts of the sensible world. In virtue 

 of our mental idiosyncrasy, we demand why bodies 



