BOOK II.] MOTION OF ACQUISITION. 541 



itself, notwithstanding its subtilty, does not penetrate the pores 

 of solid vessels at once, but only by long-continued insinuation. 



Let the sixth be that which we term the motion of acquisition, 

 or the motion of need.&quot; 1 It is that by which bodies placed 

 amongst others of a heterogeneous and, as it were, hostile 

 nature, if they meet with the means or opportunity of avoiding 

 them, and uniting themselves with others of a more analogous 

 nature, even when these latter are not closely allied to them, 

 immediately seize and, as it were, selecb them, and appear to 

 consider it as something acquired (whence we derive the name), 

 and to have need of these latter bodies. For instance, gold, or 

 any other metal in leaf, does not like the neighbourhood of air ; 

 if, therefore, they meet with any tangible and thick substance 

 (such as the finger, paper, or the like), they immediately adhere 

 to it, and are not easily torn from it. Paper, too, and cloth, and 

 the like, do not agree with the air, which is inherent and mixed 

 in their pores. They readily, therefore, imbibe water or other 

 liquids, and get rid of the air. Sugar, or a sponge, dipped in 

 water or wine, and though part of it be out of the water or 

 wine, and at some height above it, will yet gradually absorb 

 them. n 



Hence an excellent rule is derived for the opening and dissolu 

 tion of bodies ; for (not to mention corrosive and strong waters, 

 which force their way) if a body can be found which is more 

 adapted, suited, and friendly to a given solid, than that with 

 which it is by some necessity united, the given solid immediately 

 opens and dissolves itself to receive the former, and excludes or 

 removes the latter. Nor is the effect or power of this motion 

 confined to contact, for the electric energy (oi which Gilbert 

 and others after him have told so many fables) is only the 

 energy excited in a body by gentle friction, and which does not 

 endure the air, but prefers some tangible substance if there be 

 any at hand. 



Let the seventh be that which we term the motion of greater 

 congregation, by which bodies are borne towards masses of a 

 similar nature, for instance, heavy bodies towards the earth, 

 light to the sphere of heaven. The schools termed this natural 

 motion, by a superficial consideration of it, because produced by 

 no external visible agent, which made them consider it innate in 

 the substances ; or perhaps because it does not cease, which is 



* As far as this motion results from attraction and repulsion, it is 

 only a simple consequence of the two last. Ed. 



&quot; These two cases are now resolved into the property of the capillary 

 tubes, and present only another feature oi the law of attraction. Ed. 



This is one of the most useful practical methods in chemistry at the 

 present day. 



