in Free Surfaces of Liquids. 

 Fig. 3. 



143 



Alkaline solution of CaCl 2 



Oil of turpentine. 

 Ale. sol. CuCL;. 

 Alcohol. 

 Sulphide of carbon. 



From the numerical values of the last table, as well as from 

 these drawings, the following results are obtained: — 



(a) In all the liquids studied, the resistance to motion is 

 not inconsiderably augmented when the plate approaches the 

 free surface. 



(b) On a further elevation of the plate causing its upper 

 edge to enter the free surface, a characteristic difference be- 

 tween the various liquids becomes manifest, and we find, exactly 

 as Plateau states, 



I. Liquids which exhibit a considerable augmentation of 

 the resistance — water and aqueous salt-solutions; 



II. Liquids in which a diminution of the resistance occurs 

 — alcohol, alcoholic solutions, sulphide of carbon, oil of tur- 

 pentine; 



III. Mixtures of water and alcohol, which join the one 

 or the other group according to the proportion of the con- 

 stituents. 



(c) When the resistances of the liquids at greater depths 

 are compared, that of sulphide of carbon is the least; water 

 and alcohol follow, with nearly equal resistances; lastly, oil 

 of turpentine with a considerably greater resistance. The 

 addition of a salt produces in most cases a considerable aug- 

 mentation of the resistance. It is likewise to be noted as 

 remarkable, that mixtures of water and alcohol show a greater 

 resistance than either constituent by itself. 



One portion of these results admits of a simple explanation. 

 In the first place, that in all liquids the resistance increases 

 as the surface is approached is not surprising ; for the liquid 

 particles put in motion by the plate give way not only in a 



