4 PROF. OSBORNE REYNOLDS ON THE 



Evidence of Considerable Cohesion. 



These are_, for the most pai% what are considered minor 

 phenomena ; they are confined to the surface of the liquid, 

 and are included under what is called " capillarity/^ or 

 " surface-tension/^ 



The phenomena of capillarity or surface-tension have 

 recently attracted a great deal of attention ; and many im- 

 portant facts concerning them have been clearly elucidated, 

 some of which bear directly on my present subject. 



Of the phenomena I may instance the suspension of 

 drops of water, the rising of water up small tubes, the 

 tendency of bubbles to contract, and the spherical form 

 assumed by small fragments of mercury. 



These phenomena and others are found to be explained 

 by the fact that the surface of these liquids is always under 

 a slight but constant tension, as if enclosed in a thin 

 elastic membrane. 



No satisfactory explanation as to the cause of this sur- 

 face-tension has, I believe, been as yet found ; but the fact 

 itself is proved beyond all question. It is a molecular 

 phenomenon ; and in order to offer any explanation as to 

 its cause, it would be necessary to adopt some hypothesis 

 respecting the molecular constitution of the liquid. Such 

 an explanation making the surface-tension to arise from 

 the cohesion of the molecules of the liquid is, I believe, 

 possible ; but this is beside my present purpose, which will 

 be completely served by showing that 



The Surface-tension proves the existence of Cohesion. 



To prove this requires no molecular hypothesis; but, 

 before proceeding, it may be well to define clearly the 

 term cohesion. 



Cohesion in a liquid is here to be understood as a 



