AitrcB'tve Po<Ufer of Bodies jlnaiirtg on IVater. yj 



5. By means of tlie hvcfronicter the comparative value of 

 all forts of bark iDaV be calily determined. For this purpofc 

 take equal quantities of the barks to be tonipared ; infufe 

 them tiie fame number of tm.es in equal qiiantiiies of water, 

 and the hydrometer will {}iow their relative ftrength or value. 



«prj*- 



IV. On the attraBive Power of Bodies Jloaling on IVatet, 

 By Dr. G. CARRAbORl *. 



I 



F a feu- fmall dry bodies, fuch aS bits of dry leaves or faw- 

 duft, be throwfl into water and iilimerfed at about the di. 

 fiance of an inch under each other, during the time of im- 

 nierfion voii will fee the bodies feparate themfelves a little 

 from each other, dvving, aS may be readily conceived, to the 

 tfferts of the motion occaiioned bv iinmerfing them in the 

 fluid. If you then bring one of thefe bodies near to another, 

 the latter will ev^ry whefe follow the other, \Vhether vbu im- 

 jnerfe itdeepT, raile it above the water, or move it horizon- 

 tally ; and both bodies \V-.ll hang to each other, and thus ex- 

 ercife a kind of aitra<9:ive force. Tliis, howevtr, is not the 

 effecSl of the rtcipfocal attraoHon of the bbdies; for, in the 

 firll cafe, that is, when you immerfe the one body deeper, 

 ihe f)iher will endeavour to approach it, becaufe a cavity or 

 tircular vacuity i.> produced, in \\hich it muft then follow 

 the current ; and fbe caufe of this is, that the cohefive poWet 

 of ihe water is not fo ftroiig as the attraftion which it ex-^ 

 ercifes over that body, and therefore its furface always yields 

 more, and, keeping behind the bodv, puflies it forwards, and, 

 as It were, fwallows it up. This pha-nomenon is exhibited 

 by all floating bodes which "atlra(::l the water; for thev fol- 

 low the fame movement, which, according to the adhefioft 

 which it haa with the body, either rifes upwards or Onks 

 down. 



As it has been obfetved that all bodies which contain 1 

 cortyin volatile or fixed oil, orrefin, have an extenfive power, 

 whether they be fluid or hard, and, in the lall cafe, that they 

 Jail into duft as foon as thev are applied to the furface of the 

 water, I am f)f opinion that All fubftances which exhibit 

 fuch a phjenonienon contain a common oil, or refin, which 

 gives rife to it. I will u(>t here mention that feries of bodie.s 

 jlll f)f an oily or refmous luture, v ith wliich I made experi- 

 ments; but I can allert that they all produced this efleil ifi 

 ^ greater or lei's dtgree. Milk for exaniple, which, ai every 



♦ f roiTi Gternaie fijicp-Mtdic), by Pru^jnaieUi, Vol, IV. 



one 



