8 COSMOS. 



on the intellectual activity and scientific knowledge of man- 

 kind. 



All celestial bodies, excepting our own planet and the 

 aerolites which are attracted by it, are, to our conception, 

 composed only of homogeneous gravitating matter, without 

 any specific or so-called elementary difference of substances. 

 Such a simple assumption is, however, not by any means 

 based upon the inner nature and constitution of these remote 

 celestial orbs, but arises merely from the simplicity of the 

 hypotheses which are capable of explaining and leading us to 

 predict the movements of the heavenly bodies. This idea 

 arises, as I have already had occasion frequently to remark 

 (Cosmos, vol. i., p. 62-07, and p. 135-137 ; vol. in., p. 6-20, 

 and 22-24), from the exclusion of all recognition of hetero- 

 geneity of matter, and presents us with the solution of the 

 great problem of celestial mechanics, in which all that is va- 

 riable in the uranological sphere is subjected to the sole con- 

 trol of dynamical laws. 



Periodical alternations of light upon the surface of the 

 planet Mars do indeed point, in accordance with its different 

 seasons of the year, to various meteorological processes, and 

 to the polar precipitates excited by cold in the atmosphere 

 of that planet (Cosmos, vol. iv., p. 160). Guided by analo- 

 gies and reasoning, we may indeed here assume the presence 

 of ice or snow (oxygen and hydrogen), as in the eruptive 

 masses or the annular plains of the moon we assume the ex- 

 istence of different kinds of rock on our satellite, but direct 

 observation can teach us nothing in reference to these points. 

 Even Newton ventured only on conjectures regarding the 

 elementary constitution of the planets which belong to our 

 own solar system, as we learn from an important conversa- 

 tion which he had at Kensington with Conduit (Cosmos, vol. 

 i., p. 132). The uniform image of homogeneous gravitating 

 matter conglomerated into celestial bodies has occupied the 

 fancy of mankind in various ways, and mythology has even 

 linked the charm of music to the voiceless regions within the 

 realms of space (Cosmos, vol. iv., p. 108-110). 



Amid the boundless wealth of chemically varying sub- 

 stances, with their numberless manifestations of force amid 

 the plastic and creative energy of the whole of the organic 

 world, and of many inorganic substances amid the meta- 

 morphosis of matter which exhibits an ever-active appear- 

 ance of creation and annihilation, the human mind, ever 

 striving to grasp at order, often yearns for simple laws of 



