on the Adhesion between Solids and Liquids, . 195" 



with air to diminish by exposure (tbe tension of water at I0 a 

 being 7*53 milligrammes per millimetre of length, and after 

 some hours not more than 4*69 milligrammes). Hence at first 

 view there seemed to be something anomalous in the two state- 

 ments; for if both be true, then it seems to follow that the su- 

 perficial resistance opposed by the liquids to the motion of solids 

 has a different origin from that of tension. Plateau refers this 

 resistance to the viscosity of liquids. 



The increased resistance of the liquids operated on by me, in 

 consequence of a protracted exposure to the air, could only arise 

 from a more or less rapid alteration in them, either by the adhe- 

 sive action of the air or by the deposition of aerial dust. So 

 trifling a circumstance disturbs the purity of a liquid, that it is 

 sufficient in some cases to touch it with the tip of the finger to 

 prevent its adhesion to other liquids. Hence the action of dust 

 from the air will readily be understood. 



The increased resistance, then, of the liquids in proportion to 

 the continued contact with the solids is easily explained, seeing 

 that this prolonged contact allows an increased mass of liquid to 

 adhere to the solid. Such an increase of adhesion takes place 

 between solids, and still more between solids and liquids. A 

 clean plate of brass put into fresh water comes out all but dry ; 

 let it remain in the water some hours, and on taking it out the 

 wetted portions will be found to have increased with the duration 

 of the immersion. This effect is best seen by sinking the plate 

 horizontally in the water and withdrawing it in the same position. 

 This effect specially applies to plates of glass and of steel upon 

 and within mercury. The mercury was washed, dried, and fil- 

 tered, and it appeared bright and clean, but it readily dragged a 

 tail on being moved about on glass or steel. Yet these plates, 

 both on the surface of mercury and below it*, yielded to the 

 torsion of the filament and began to move; but in a few minutes 

 they met with so much resistance as no longer to move except 

 under the torsion of a stronger filament. On examining the 

 plates, it was found that the points attacked by the mercury 

 became more numerous and extensive the more the contact was 

 prolonged. I hope to repeat these experiments with purer 

 mercury. 



3. The resistance of one and the same liquid varies with the 

 nature of the solid. If, instead of a steel needle, M. Plateau had 

 used one of glass or other material, his results would have been 



* The torsion-line has near its lower extremity a leaden bullet sur- 

 mounted by a small capsule ; and the body to be experimented on is attached 

 to the bullet in various ways according to circumstances. The small cap- 

 sule is for the reception of shot, for the purpose of maintaining the line at 

 nearly constant tension, whether the body be in air, on the surface of the 

 liquid, or below it. 



