THE SURFACE TENSION OF LIQUIDS. 



599 



appear swimming over the surface of the mercury (Fig. 7). If, 

 now, we breathe continuously from one side upon the mercury, 

 the "tadpoles" will become more lively, and direct themselves 

 against the breath, coming up to the very edge of the mercury. 

 The breath, driving the vapors back, clears a space in front of the 

 " tadpole," leaving the tension of the mercury free to act upon 

 it and draw it forward, while it clouds the rear, weakening the 

 tension. 



M. Devaux has exemplified the strength and persistence of the 

 tensional force by connecting his camphor-boat with a float in the 

 shape of a watch-glass. The movement of the boat continues, car- 



Fig. 8. — Tin Boat causing a Loaded Float to go round with it. 



rying the float around while it is loaded with weights rising to 

 fifty or a hundred grammes, and even to a kilogramme (Fig. 8) ; 

 and if forcibly stopped, it will begin again when the obstacle is 

 removed. 



The phenomena of capillary attraction are explained under the 

 theory of superficial tension. The liquid rises in the tubes by vir- 

 tue of the adhesion of its superficial membrane to their walls, and 

 to a less height in the larger than in the smaller tubes because 

 the mass of the liquid to be raised increases more rapidly than 

 the power of the membrane to sustain it. Just as the tension of 

 a liquid is diminished by adding a foreign substance, the capillary 

 force of a tube is diminished by the presence of a foreign vapor. 

 This is illustrated by M. Devaux as in Fig. 9, where water rises 

 to the greatest height in the tube A, which was filled simply with 

 air, to a less height in E, which has been charged with the vapor 

 of ether, and to a still less height in C, which was occupied with 

 the vapor of camphor. 



Other energies than this mechanical energy have been shown 



