INTRODUCTION. V 



motion in the investigation of the terrestrial sphere. Even 

 Aristotle, in his Physics, states that " the fundamental prin- 

 ciples of all nature are change and motion ; he who does not 

 recognize this truth recognizes not Nature herself" {Phys. 

 Auscult, iii., 1, p. 200, Bekker), and, referring to the differ- 

 ence of matter ("a diversity in essence"), he designates mo- 

 tion, in respect to its qualitative nature, as a metamorphosis, 

 dXXoto)Gig, very different from mere mixture, fJil^ig, and a 

 penetration which does not exclude the idea of subsequent 

 separation {De Gener. et Corrujit., i., 1, p. ,327). 



The unequal ascent of fluids in capillary tubes — the endos- 

 mosis which is so active in all organic cells, and is probably 

 a consequence of capillarity — the condensation of different 

 kinds of gases in porous bodies (of oxygen in spongy plati- 

 num, with a pressure which is equal to a force of more than 

 700 atmospheres, and of carbonic acid in boxwood charcoal, 

 when more than one third is condensed in a liquid state on 

 the walls of the cells) — the chemical action of contact-sub- 

 stances, which by their presence occasion or destroy (by ca- 

 talysis) combinations without themselves taking any part in 

 them — all these phenomena teach us that bodies at infinitely 

 small distances exert an attraction upon one another, which 

 depends upon their specific natures. We can not conceive 

 such attractions to exist independently of motions, which 

 must be excited by them although inappreciable to our eyes. 



We are still entirely ignorant of the relations which recip- 

 rocal molecular attraction as a cause of unceasing motion 

 on the surface, and very probably also in the interior of the 

 earth's body, exerts upon the attraction of gravitation, by 

 which the planets as well as their central body are main- 

 tained in constant motion. Even the partial solution of this 

 purely physical problem would yield the highest and most 

 splendid results that can be attained in these paths of in- 

 quiry, by the aid of experimental and intellectual research. 

 I purposely abstain in these sentences from associating (as is 

 commonly done) the name ^f Newton with that law of at- 

 traction which rules the celestial bodies in space at bound- 

 less distances, and which is inversely as the square of the 

 distance. Such an association implies almost an injustice 

 toward the memory of this great man, who had recognized 

 both these manifestations of force, although he did not sepa- 

 rate them with sufficient distinctness; for we find — as if in 

 the felicitous presentiment of future discoveries — that he at- 

 tempted, in the Queries to his Optics, to refer capillarity, and 



A 2 



