u 



COHESION OF FLT7IDS. 



AppUation of ijjq^jjrjjjjy v^^gj- j^^^^^ be the circumference of the fluid', that 



tiic aoctnnc to ' " ... 



}>artioiviar would support by its cohesion the weight of a hemisphere de- 



''"'•^^' pending from it : tliis must be the same ns that of a tube, in 



■which the fluid would rise to the height of one-third of its dia- 

 meter ; and the square of the diameter must be three times as 

 l^rcat as the appropriate product; or, for water .12; whence 

 fhe diuincler would be .35, or a little more than one-third of 

 an inch, and the weight of the hemisphere would be 2.8 

 grains. If more water were added internally, the cohesion 

 would be overcome, and the drop would no longer be suspen- 

 ded, but it is not easy to cakulate what precise quantity of 

 water would be separated with it. The form of a bubble of 

 air rising in water is determined by the cohesion of the inter- 

 nal surface of th« water exactly in the same manner as tht 

 form of a drop of water in the air; The delay of a bubble of 

 ail- at the bottom of a vessel appears to be occasioned by a 

 dcticiency of the pressure of tlic water between the air and the- 

 vessel ; it is nearly analogous to the experiment of making a? 

 piece ot' wood remain inmieised in water, when perfectly in 

 contact with the bottom of the vessel containing it. This ex- 

 periment succeeds however far more readily with mercury^ 

 since tj.e capillary cohesion of the mercury prevents its in- 

 siuu*ititig itbelf under the wood. 



, V. Of appare?]i Attractions and Bepulsions. 

 On the appa- The apparent attraction of two floating bodies, round both; 

 any^'n-ptuions of wliich the fluid is raised by cohesive atiraction,, is produ- 

 of floatiiijf ced by the ejsccss of the atmospheric pressure on the remote 



sidesjof the solids above its pressure on their neighbouring 

 sidcsi: or, if the experiments are performed in a vacuum, by 

 the Jquiialciu hydrostatic pressure or suction derived from 

 the leight and iuimecliate cohesion of the intervening fluid.. 

 This force varies ultimately in the inverse ratio of the square 

 of tlie difctimce ;. for, if two plates approach each otJIicr,. the 

 heigliit of tlic fluid that rises between them is increased in the 

 / simple inverse ratio of the distance ; and- the mean action, or 



negative pressure, of the fluid on each particle of the surface 

 is also increased in the same ratio. When the floating bodies- 

 are b:)th surrounded by a depression, the same law prevails, 

 andils demon!- tratiou is still more simple and obvious. I'he 



repul- 



