CAPILLARY ACTION. 591 



RELATION OF SURFACE-TENSION TO TEMPERATURE. 



It appears from the experiments of Brunner and of Wolff on the ascent 

 of water in tubes that at the temperature t" centigrade 



r= 75-20 (i-o-ooi 87*); 



= 76-08 (1-0'002 + 0'00000415 2 ), for a tube '02346cm. diameter (Wolff) ; 

 = 77-34(1-0-001810, for a tube '03098cm. diameter (Wolff). 



Sir W. Thomson has applied the principles of Thermodynamics to deter- 

 mine the thermal effects of increasing or diminishing the area of the free surface 

 of a liquid, and has shewn that in order to keep the temperature constant 

 while the area of the surface increases by unity, an amount of heat must be 

 supplied to the liquid which is dynamically equivalent to the product of the 

 absolute temperature into the decrement of the surface-tension per degree of 

 temperature. We may call this the latent heat of surface-extension. 



It appears from the experiments of Brunner and Wolff that at ordinary 

 temperatures the latent heat of extension of the surface of water is dynamically 

 equivalent to about half the mechanical work done in producing the surface- 

 extension. 



