a Chemically Clean Surface. 247 



other films. For example, oleine of fish-oil will displace castor- 

 oil, pale seal-oil will displace oil of nutmegs, and so on. 



In all these cases, although dealing with essential and fatty 

 oils, strict attention must be paid to chemical purity. If the 

 vessel or the water-surface be not chemically clean, the oils will 

 form lenses and not films. But if clean, the oils, in being shut 

 up or in moving about, leave no trails on the surface, and the 

 creosote is as free and active in its motions as if no fatty oil were 

 present. It is, in fact, a case of adhesion, in which the attraction 

 between water and creosote is superior to that between water and 

 the oils : even where an essential oil like turpentine arrests the 

 motions of the creosote for a time, it does not displace the creo- 

 sote; for this retains its hold on the water, and, when the adhe- 

 sion of the oil-film has become weakened by evaporation &c, the 

 creosote reassumes its rule over the w r hole surface. 



There are, however, some liquids which cany with them cer- 

 tain purifying influences of their own, and impart them to the 

 water and the vessel. Such are ether, absolute alcohol, wood- 

 spirit, &c, which most readily form cohesion-figures, as noticed 

 in my first paper on this subject*. There is also a phenomenon 

 that may be noticed every time a glass of wine is drunk — known, 

 I believe, as the "weeping of the wine/' or "tears in the cup/' 

 and may possibly explain a passage in the Book of Proverbs (xxiii. 

 31) as to when wine "moveth itself aright" in the cup. When 

 a glass is filled with wine (the stronger the better), the alcohol 

 and vinic ether make the glass chemically clean; a sip is taken 

 and the glass one third or one half emptied. The part of the 

 glass between the original level and the reduced level is com- 

 pletely wetted by the wine, and there is a strong capillary action 

 between the reduced level and the plate of liquid left on the glass. 

 But the supply of liquid above the surface of the wine in the 

 glass is kept up by a twofold action. In the spaces between 

 the tears will be seen an ascending wavy current of liquid which 

 rises (1) by the adhesive action of capillarity, (2) by the forma- 

 tion of a back current in consequence of the downward flow of 

 the tears, just as a backwater is formed at the place where two 

 currents of a river meet ; and this action, in the case of a glass 

 of w r ine, will be rendered more apparent, in the same way as we 

 see it in a river, if there are any specks or floating particles 

 moving on the surface to show its direction. 



The motions of eugenic acid on the surface of water f form a 

 kindred phenomenon on a horizontal plane, to the tears in the 

 wine-glass on a vertical one. But in some cases tears are due 



* Phil. Mag. for October 1861. 



f See Phil. Mag. for July 1864 (Suppl). This experiment also requires 

 a clean water-surface. 



