CAPILLARY ACTION. 



experiment. The only difference is in the manner in which this quantity // 

 depend* on the law of the molecular forces and the law of density near the 

 mr&ee of the fluid, and as these laws are unknown to us we cannot obtain 

 any te*t to discriminate between the two theories. 



Wa haw now described the principal forms of the theory of capillary 

 action during its earlier development. In more recent times the method of 

 GAUM has been modified so as to take account of the variation of density 

 near the surface, and its language has been translated in terms of the modern 

 doctrine of the conservation of energy *. 



M. Plateau t, who has himself made the most elaborate study of the 

 phenomena of surface-tension, has adopted the following method of getting rid 

 of the effects of gravity : He forms a mixture of alcohol and water of the 

 same density as olive oil. He then introduces a quantity of oil into the 

 mixture. It assumes the form of a sphere under the action of surface-tension 

 alone. He then, by means of rings of iron-wire, disks, and other contrivances, 

 alters the form of certain parts of the surface of the oil. The free portions 

 of the surface then assume new forms depending on the equilibrium of surface- 

 tension. In this way he has produced a great many of the forms of equilibrium 



a liquid under the action of surface-tension alone, and compared them with 

 the results of mathematical investigation. He has also greatly facilitated the 



idy of liquid films by shewing how to form a liquid, the films of which 

 will last for twelve or even for twenty-four hours. The debt which science 

 owes to M. Plateau is not diminished by the fact that, while investigating 

 these beautiful phenomena, he has never himself seen them. He lost his sight 

 long ago 1 in the pursuit of science, and has ever since been obliged to depend 

 on the eyes and the hands of others. 



M. Van der Mensbrugghe J has also devised a great number of beautiful 

 illustrations of the phenomena of surface-tension, and has shewn their connection 

 with the experiments of Mr Tomlinson on the figures formed by oils dropped 

 on the clean surface of water. 



* See Prof. Betti, Teoria delta CapillaritA: Nuavo Cimento, 1867; a memoir by M. Stahl, 

 "Ueber einige Punckto in der Theorie der Capillarerscheimmgen," Pogg. Ann., cxxxix. p. 239 (1870); 

 and M. Van der Waal's Over da Continuiteit van den Gcu- en Vloeistoftoesland. The student will 

 find a good account of the subject from a mathematical point of view in Professor Challis's 

 "Report on the Theory of Capillary Attraction," Brit. Ass. Report, iv. p. 253 (1834). 



t M. Plateau, Statique experimental* et theorique des liquides. 



J J/em. d* FAcad. Roy. de Belyiqu*, xxxvn. (1873). 



