52 POPULAR LECTURES AND ADDRESSES. 



the space through which the rising ring has 

 passed.* 



These phenomena may also be observed by 

 using, instead of alcohol, ether, which has a sur- 

 face-tension equal to about three-fourths of that 

 of alcohol. In using ether, however, this very 

 curious effect may be seen/f I dip the brush into 

 the ether, and hold it near to but not touching 

 the water-surface. Now I see a hollow formed, 

 which becomes more or less deep according as 

 the brush is nearer to or farther from the normal 

 water-surface, and the hollow follows the brush 

 about as I move it so. 



Here is an experiment showing the effect of heat 



* The following paragraph, quoted from Clerk-Maxwell's "Heat," 

 Ed. 1871, p. 273, contains an interesting reference to this part of 

 our subject. 



''This phenomenon, known as the tears of strong wine, was first 

 explained on these principles by Professor James Thomson. It is 

 probable that it is referred to in Proverbs xxiii. 31, as an indication 

 of the strength of the wine. The motion ceases in a stoppered 

 bottle as soon as enough of vapour of alcohol has been formed in 

 the bottle to be in equilibrium with the liquid alcohol in the wine." 



t See Clerk-Maxwell's article (p. 65) on " Capillary Attraction " 

 (" Encyclopaedia Britannica," 9th edition). 



