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XXVI. On Capillary Attraction. By the Rev. J. B. Emmett.* 



THHE phaenomena of capillary attraction are amongst the 

 -^ most curious and obscure in nature. The spontaneous 

 rise of liquids between solid surfaces placed very near to each 

 other, proves that corpuscular attraction does extend to a 

 distance equal to several diameters of the particles of the 

 suspended liquid, so as greatly to exceed their weight. Hence 

 the elevation is occasioned by the corpuscular force acting 

 perpendicularly to the axis of the tube, on the same principles 

 as common hydraulic pressure: if the corpuscular force exist, 

 and extend its powers to the distance of several rows of par- 

 ticles of the liquid, all the observed phnenomena will result f. 

 Hence also, corpuscular attraction varies reciprocally as the 

 square of the distance from the centre of each particle:]:. Its 



power 



• Communicated by the Author. 



t A force acting perpendicularly to the axis of the capillary tube, and 

 exceeding in intensity the force of gravity of the particles at such, still in- 

 sensible, distances, will act thus. The most remote stratum of the liquid, 

 which is acted upon, tends to the side of the tube, with a certain force ; 

 with this force it presses upon all the nearer strata ; each of which like- 

 wise tends to the tube, with a force which varies according to some func- 

 tion of the distance. Hence each stratum is pressed by the sum of all 

 the tendencies of the strata beyond it, which are sensibly acted upon ; the 

 liquid being supposed incompressible. The acting force being inversely as 

 the nth power of the distance from the tube; to a right line, erect perpen- 

 dicular ordinates, which shall vary in this ratio: draw a curve passing 

 through their extremities, and its area will represent the whole pressure upon 

 the solid : or if solids possess different forces of attraction for the same or 

 different liquids, describe more such curves, making one given ordinate in 

 one to the corresponding ordinate of another curve, as one force is to an- 

 other force; and their areas will be proportional to these pressures. The 

 liquid cannot be at rest, until this force is balanced by an equal and oppo- 

 site force : this force can be no other than the weight of the elevated co- 

 lumn : and that such a column will be raised, is evident from the principles 

 of hydraulic pressure. The hypothesis of the attraction of an annulus of the 

 tube raising the liquid cannot explain the phaenomena; and particularly 

 that of the rise of the liquid around a rod partly immersed : for no annulus 

 can be found, which has not an equal and equidistant annulus, exerting 

 an equal force in an opposite direction. 



X For (Newtoni Princip. lib. i. prop. 87.) supposing a force of attraction 

 to vary rccii)rocally as the cube of the distance ; if similar solids be taken, 

 of equally attracting matter, they will equally attract corpuscles, similarly 

 situated. Now from the specific gravities of a liquid and of the same mat- 

 ter in a solid state, the ratio l)etween the diameter and distance of adjacent 

 particles in the liquid may be known. Now, the force of attraction be- 

 tween some solids, as glass, and some liquids, as water, so greatly exceeds the 

 weight of the li(|uid particles, at a distance equal to several of their diame- 

 ters, as not only to support themselves, but an indefinitely great number be- 

 sides them. Form an elementary cone, whose vertex shall be in the axis 

 of the capillarv tube, and whose axis shall be perpendicular to the axis of 

 Q 2 the 



