322 Prof. G. Quincke on the Edge~angle and 



Imagine several fluids in contact with one another (for ex- 

 ample a lenticular drop of water upon oil or mercury) and let 

 them be gradually cooled down : the water will finally freeze. 

 The attraction between the particles of oil or mercury and the 

 particles of the frozen drop of water will differ only by an in- 

 considerable quantity from the attraction which they would 

 have exercised upon the particles of the fluid drop of water. 

 The common surface between the oil or mercury and the water 

 will have similar properties whether the water be fluid or solid ; 

 and in the common surface of oil and ice, or of mercury and 

 ice, a surface-tension ol x 2 must exist similar to that in the com- 

 mon surface of oil and water or of mercury and water. 



Moreover the ready mobility of the particles of oil or of mer- 

 cury amongst one another, and especially their mobility with 

 respect to the now immovable particles of water, will probably 

 have been changed. 



A similar consideration may be applied to other bodies in 

 the liquid and solid conditions as to liquid and solid water ; 

 and hence we arrive at the following universal proposition : — 



In the common bounding surface of a fluid 2, and of a solid 

 body 1, there exists a surface-tension a 12 , as in the common 

 boundary of two fluids. 



This surface-tension will be the same within the fluid and 

 within the solid body, provided only the particles are imme- 

 diately on the common (geometrical) boundary of both sub- 

 stances. The surface-tension will be perceptible only under 

 special circumstances in the solid body, whose particles are very 

 difficultly movable amongst one another, but more easily in 

 the fluid layer which bounds the surface of the solid body. 



It might therefore be assumed, to return to the previously 

 mentioned special case, that a capillary surface-tension existed 

 not only in the capillary surface of the frozen drop of water 

 bounded by mercury, but also in the free surface of the frozen- 

 drop bounded by air — a surface-tension which would have 

 the same value for all points of the free surface, and which 

 must be independent of its geometrical figure. 



The fluid layer at the common bounding surface of a solid 

 body 1 and of a fluid 2 would therefore behave as a stretched 

 membrane having at all points a constant surface-tension 



The action of the particles of the solid body upon a fluid 

 particle at the point P is such as if there acted in the free sur- 

 face of the solid body bounded by air, a constant surface-tension 

 a 1? independent of the geometrical figure of the surface, having 

 the same value for every fluid particle P of the intersecting line 

 of the capillary surface. 



