10 COSMOS. 



the little that was then known of chemical affinity, to univers- 

 al gravitation (Laplace, Expos, clu Syst. die Monde, p. 384. 

 Cosmos, vol. iii., p. 23). 



As in the physical world, more especially on the borders 

 of the sea, delusive images often appear which seem for a 

 time to promise to the expectant discoverer the possession of 

 some new and unknown land ; so, on the ideal horizon of 

 the remotest regions of the world of thought, the earnest in- 

 vestigator is often cheered by many sanguine hopes, which 

 vanish almost as quickly as they have been formed. Some 

 of the splendid discoveries of modern times have undoubtedly 

 been of a nature to heighten this expectation. Among these 

 we may instance contact-electricity — magnetism of rotation, 

 which may even be excited by fluids, either in their aqueous 

 form or consolidated into ice — the felicitous attempt of con- 

 sidering all chemical affinity as the consequence of the elec- 

 trical relations of atoms with a predominating polar force — 

 the theory of isomorphous substances in its application to 

 the formation of crystals — many phenomena of the electrical 

 condition of living muscular fibre — and, lastly, the knowledge 

 which we have obtained of the influence exerted by the sun's 

 position, that is to say, the thermic force of the solar rays, 

 upon the greater or lesser magnetic capacity and conducting 

 power of one of the constituents of our atmosphere, namely, 

 oxygen. When light is unexpectedly thrown upon any pre- 

 viously obscure group of phenomena in the physical world, 

 we may the more readily believe that we are on the thresh- 

 old of new discoveries, when we find that these relations ap- 

 pear to be either obscure, or even in opposition to already 

 established facts. 



I have more particularly adduced examples in which the 

 dynamic actions of attracting forces seem to show the course 

 by which we may hope to approximate toward the solution 

 of the problem of the original, unchangeable, and hence 

 named the elementary heterogeneity of substances (for in- 

 stance, oxygen, hydrogen, sulphur, potassium, phosphorus, 

 tin, etc.), and of the amount of their tendency to combine ; 

 in other words, their chemical affinity. Differences of form 

 and mixture are, I would again repeat, the only elements of 

 our knowledge of matter; they are the abstractions under 

 which we endeavor to comprehend the all-moving universe, 

 both as to its size and composition. The detonation of the 

 fulminates under a slight mechanical pressure, and the still 

 more formidable explosion of terchloride of nitrogen, which 



