On the Spread of Liquids on Solid Bodies. 415 



only with the direction of the current, but likewise with its 

 strength, and to some extent also with its duration. To con- 

 struct a selenium resistance for exact measuring-purposes, 

 coefficients for all these changes would have to be determined, 

 at very considerable trouble ; and when determined, the in- 

 constancy of the material is such that they would probably 

 soon be altogether inapplicable. 



In preparing the apparatus and making the experiments, I 

 have been greatly indebted to the efficient aid rendered me by 

 Mr. McEniry. 



Grosmont House, Hampton Wick, 

 May 1, 1878. 



LVIII. On the Edge-angle and Spread of Liquids on Solid 

 Bodies. By Gr. Quincke. 



[Concluded from p. 339.] 



10. SPREAD of Liquids upon the Surface of Solid Bodies. 

 — It is possible to form an opinion in another manner 

 than by direct measurements, about the magnitude of the 

 surface-tension at the boundary of a fluid and of a solid body, 

 from the magnitude of the edge-angle which a fluid-surface 

 forms with a solid body. 



From equation (5) follows at once 



«21>«13> 



if the edge-angle 6 of the common boundmg-surface of the 

 fluids 2 and 3 with the solid body 1 is an acute angle for 

 fluid 3. 



For glass as the solid body, and water as fluid 3, and for 

 bisulphide of carbon, chloroform, olive-oil, turpentine, petro- 

 leum, or mercury as fluid 2, this condition is fulfilled with 

 the slight allowances already explained* for impurity of the 

 solid surface of glass. 



The water will therefore have a greater adhesion to glass 

 than the fluids named. 



Whenever free fluid-surfaces bounded by air are absent, none 

 of the fluids 2 investigated drives the water away from the 

 glass surface, however different in magnitude may be their 

 capillary constants. The edge angle was only in rare cases 0° ; 

 consequently the water also usually did not drive the other 

 fluids from the glass surface. 



* Compare the researches upon flat drops and bubbles, Pegg. Ann. 

 cxxxix. pp. 18-20, 22 (1870) ; upon submerged capillary tubes, ibid. pp. 

 42-44 ; upon the ascent in capillary tubes of several superposed fluids, 

 ibid, pp. 50-52. And in Phil. Mag. April, May, and June, 1871. 



