45 S Dr. Wall on. AttraSlion and Repulfton. 



•*' attraftion (the mechanical and the chemical) 

 *' fhould be properly diftinguidied and feparated 

 ** from each other, as many errors have arifen, 

 ** from applying to one, fuch laws only as obtaip 

 " in the other." 



Your illuftration of repulfion, from the beau« 

 tiful appearance of the drops of water on cole- 

 wort leaves, feems, at firfl: view^, to prefent a 

 moil forcible objedion to my fyftem ; and yep 

 perhaps upon more mature confideration, that 

 fafl may be aflumed as a confirmation of it. 

 For water, from the (Irong attradlion of its 

 particles to each other, efpecially when the quan- 

 tity is inconfiderable, and is allowed to fall upoa 

 an inclined furface, does not adhere to that fur- 

 face, but forms itfelf into globules, and runs off, 

 till by the breaking of fome of the drops, or the 

 accidental remora of others, that furface becomes 

 wetted, and then the drops no longer exhibit 

 the property above-mentioned. And this is 

 fometimes remarkable, even when the water falls 

 upon fubftances, v/hich in other circumftances 

 are much difpofed to imbibe it, and to unite 

 with it; as when water is let fall from a height 

 on a furface covered with dufr, with flour, &c. 

 And a fimilar (late may obtain upon colewort, 

 and fome other large leaves, which are (iTiooth, 

 and are liable, after a dry feafon, to become 

 covered with the fine duft that floats in the air j 

 or pofTibly, there exfudes on the furface of fuch 



leaves 



