INTERNAL COHESION OF LIQUIDS. 5 



property which enables the fluid to resist any tendency 

 to cause internal separation of its parts — any tendency 

 to draw it asunder -, or, more definitely, it is the property 

 which enables a liquid to resist a tension or negative 

 pressure. 



Let us suppose a mass of liquid without internal cohesion. 

 Then any external action tending to enlarge the capacity 

 within the bounding surface of the liquid would at once 

 cause the interior of the liquid to open, and a hollow would 

 be formed within the liquid without any resistance on the 

 part of the liquid. Such a condition is inconsistent with 

 surface-tension; for the tension of the sui'face of the 

 internal hollow would tend to contract the hollow ; and 

 since the interior of the hollow is supposed to be empty, 

 there could be no resistance to the tendency of the surface 

 to contract, such as that offered by the pressure of the gas 

 within an ordinary bubble. Hence any force that might, 

 under the circumstances, balance the surface-tension and 

 keep open the hollow must be supplied by the suction or 

 cohesion of the liquid outside. — Q. E. D. 



Again, the intensity of the cohesion is determined by the 

 intensity of the surface-tension and the smallness of the least 

 possible opening over the surface of which tension exists. 



So far as has yet been determined by experiment, it 

 has been found that the surface-tension is independent of 

 the curvature of the surface — is constant for the same liquid. 

 Assuming that this is the case, it follows that the intensity 

 of the force necessary to keep a spherical bubble or opening 

 from contracting (whether this force arises from the pres- 

 sure of the gas within the bubble or the cohesive traction 

 of the liquid without the opening) is equal to twice the 

 intensity of the surface-tension divided by the radius of 

 the sphere. Hence the cohesive tension must be equal to 

 ttvice the surface-tension of the liquid divided by the diame- 



