INTERNAL COHESION OF LIQUIDS. 7 



tension due to the temperature under ordinaiy circum- 

 stances, this would be inappreciable. So that, unless the 

 tension of vapour within small openings were much greater 

 than that in larger openings for the same temperature, its 

 effect might be neglected ; and so far from this being the 

 case. Sir William Thomson has shown that the pressure of 

 the vapour within a bubble at any particular temperature 

 diminishes with the size of the opening. Hence it is clear 

 that this vapour can have no effect on the result — a con- 

 clusion verified by the now well-known fact that water 

 may be raised to a temperature high above 212° without 

 passing into steam. 



Experimental Verification necessary. 



This line of reasoning has been apparent to me now for 

 several years. I find notes on some of the principal points 

 which I made in 1873 ; ^^^ ^^^ several years I have pointed 

 out the conclusions arrived at as regards the probable 

 cohesion of water to the students in the engineering class 

 at Owens College. I have, however, hitherto refrained 

 from publishing my views, because I had no definite 

 experimental results to appeal to in confirmation of them. 

 Experimental indications of such a cohesive force were not 

 wanting, but they were not definite. And although me- 

 thods of making definite experiments have often occupied 

 my thoughts, certain difficulties, which turn out to have 

 been somewhat imaginary, kept me from trying the expe- 

 riments. 



It had always appeared to me that, in order to subject 

 the interior of a liquid mass to tension, it would be neces- 

 sary to, as it were, hold the surface of the liquid at all 

 points to prevent its contracting. To accomplish this, it 

 was necessary to have the liquid in a vessel, to the surface 

 of which the liquid would adhere as water adheres to glass. 



