420 Mr. C. Tomlinson on the Motions of Camphor 



of the surface tension of liquids. The researches of Segner 31 in 

 175 1, and of Dr. Thomas Young 32 in 1806, rendered it very- 

 probable that there existed a contractile force or tension at the 

 surface of liquids. The labours of Henry 33 , Lamarle 34 , Dupre 

 de Rennes 35 , Van der Mensbrugghe 36 ', and others have con- 

 verted this probability into a certainty ; so that the existence of 

 such a force (which is a more perfect definition of Carradori's 

 attraction of surface (9), and of Dutrochet's epipolic force (23)) 

 is not only capable of proof, but can also be expressed numeri- 

 cally for different liquids at a given temperature. As this force 

 cannot be said to be yet recognized in our Manuals of Physics, 

 perhaps I may be excused for quoting the following lines from 

 one of the few books, intended for the use of the student, in 

 which it is noticed : — 



" Every liquid possesses a certain amount of tenacity or direct 

 cohesion, whereby its parts resist separation by being directly torn 

 asunder. This cohesion has been proved to be the result, in 

 whole or in part, of an attractive force between the particles of the 

 liquid, which acts at appreciable though exceedingly small dis- 

 tances; in consequence of which there exists at the external 

 surface of every liquid mass a layer or film of liquid of unknown 

 but exceedingly small thickness, which is of somewhat less den- 

 sity than the internal mass of liquid, and consequently in a state 

 of tension. This superficial tension is the force which sustains 

 a hanging drop ; and its amount may be computed from the 

 weight and dimensions of the largest drop of the liquid which 

 can hang. It causes the surface of every isolated mass of liquid 

 (such as a falling drop), or cavity in a mass of liquid (such as 

 an air- bubble), to contract to the smallest possible dimensions, 

 and consequently to assume the figure of a sphere. It also 

 causes the surface of every isolated jet of liquid to tend to as- 

 sume a form of circular section, or to oscillate about such a form. 

 It modifies the form of the surface of every mass of liquid by 

 rounding more or less the corners, which would otherwise be an- 

 gular. Cohesion also exists to a greater or less degree between 

 liquids and solids; and the combined effects of this force and of 

 the superficial tension due to the cohesion of the liquids them- 

 selves, constitute what are known as phenomena of capillary at- 

 traction. It is by reason of this tendency of the external film 

 of a liquid mass to assume a definite figure, viz. the sphere, that, 

 in defining the word ' liquid/ non-resistance to change of figure 



31 Dc Figuris Superficierum fiuidarum comment. Gotting. 1/51. 



32 Phil. Trans. 1805. Essay on the Cohesion of Fluids, p. 65. 

 3i Phil. Mag. 1845. 



34 Mem. de V Acad. Roy. de Belgique, 18G4. 



35 Ann. de Chim. et de Phys. Ser. 4, vols, vii., ix., &c. 

 Bull, de V Acad. Roy. de Belgique, vols, xxii., xxiii. 



