INTRODUCTION. 9 



of the planets belonging to the same solar system, as we 

 learn from an important conversation held by him with 

 Conduit at Kensington (Kosmos, Bd. i. S. 137 and 407 ; 

 Engl. p. 1 22 and 389) . The uniform spectacle of apparently 

 homogeneous gravitating matter aggregated in celestial orbs 

 has struck the imagination of man in various ways, the most 

 remarkable instance being, perhaps, the myth which lends 

 to the soundless deserts of space the magic of musical tones 

 (Kosmos, Bd. iii. S. 437439 ; Engl. p. 315317). 



In the all but infinite variety of chemically-distinct sub- 

 stances, and the manifestations of force which they exhibit, 

 in the formative and productive activity of the whole of 

 organic nature, and of many inorganic substances, and in 

 the changes which produce the never-ending appearance of 

 origination and destruction, the order-seeking intellect, 

 ranging through the terrestrial d9main, looks, often unsatis- 

 fied, for simple laws of motion. In the Physics of Aristotle, 

 it is said, "the fundamental principles of all nature are 

 variation and motion ; whoso does not recognise these, does 

 not recognise nature'' (Phys. Auscult. iii. 1, p. 200, Bekker) ; 

 and, alluding to " diversity of substance," " difference of 

 essence," he terms motion, in respect to the category of 

 " qualitatives," " transformation," aXAoiwo-ie a term very 

 different from simple " mixture,'' pi&s, and an interpene- 

 tration, winch does not exclude re-separation (De gener. et 

 corrupt, i. 1, p. 327). 



The unequal ascent of fluids in capillary tubes; en- 

 dosmose, so active in all organic cells, which is probably a 

 consequence of capillarity; the condensation of gases in 

 porous bodies (oxygen gas in platinum under a pressure of 

 above 700 atmospheres, and carbonic acid gas in beech* 



