196 Prof. Luvini on the Adhesion between Solids and Liquids. 



different from those actually obtained by him. I will cite a single 

 example in support of this. One day I had a plate of tinned 

 iron in contact with the surface of water, and noticed that the 

 water became sensibly changed by the oxidation of the iron and 

 other influences that I could not explain. Now this plate of 

 tinned iron and a similar plate of brass experienced an equal re- 

 sistance on the surface of the water thus changed, while below 

 the surface the resistance encountered by the brass was consider- 

 ably less than that encountered by the tinned plate. 



4. The resistance offered by the surface of liquids to solids 

 may be distinguished into linear and superficial, while below the 

 surface the resistance is superficial only. This distinction, though 

 simple, is important. The resistance which the body encounters 

 when its surface is in contact with the liquid is different as com- 

 pared with the resistance it meets with at the line of separation 

 between the surface of the liquid and the upper external surface 

 of the solid. I name this latter the linear resistance, the former 

 the superficial. The linear does not exist when the body is totally 

 immersed in the liquid, w T hile the superficial in the case of thin 

 plates so immersed has a value sensibly double that which is 

 experienced at the surface. 



The apparent complications and irregularities in the results 

 obtained when using metallic solids of various forms and contours 

 disappeared as soon as I had made the above distinction. With 

 plates of the same material in the same liquid I found, in some 

 cases depending on the form, less resistance below the surface, 

 as happened to Plateau with the needle in the water and nume- 

 rous saline solutions; while in other cases there was a less 

 amount of resistance at the surface of the liquid, contrary to the 

 results given by Plateau. 



The theory is easy, and naturally follows from the phenomena. 

 Let X be the linear resistance and a- the superficial. The total 

 resistance on the surface of the liquid is X -f cr. Below the sur- 

 face, for thin plates it is 2o\ But X depends on the contour of 

 the plate, a on the superficies ; and it will be understood that 

 whatever be the linear resistance for every unit of length, and 

 the superficial for every unit of superficies, dependent on the re- 

 lation of the contour to the superficies of the plate, we thus get 

 for one and the same plate, and one and the same liquid, one of 

 three cases : 



X-f<7>2<7, \ + ar = 2cr, \-fO"<2<7. 



If M. Plateau will repeat his experiments with a magnetic 

 needle in which the greater diagonal is equal to that of the 

 needle already used by him, and with the minor diagonal equal 

 to the half of the major, he will probably obtain results different 



