598 PLATEAU ON THE PH.ENOMENA OP A FREE LIQUID MASS 



12. Instead of causing the solid system to penetrate the inte- 

 rior of the liquid mass, let it simply be placed in contact with 

 the external surface of the latter. An action being then esta- 

 blished at a point of the superficial layer, equilibrium must be 

 desti'oyed, and the figure of the liquid mass ought again to be 

 modified. This really occurs ; the mass becomes extended upon 

 the surface presented to it, and consequently acquires a different 

 shape. This result might also have been anticipated from what 

 occurs under ordinary circumstances, when a drop of water is 

 placed upon a previously moistened solid surface. One might 

 be induced to believe, that, as regards the actual result, this case 

 is referable to that of the preceding paragraph or that in para- 

 graph 10 ; for it appears that the liquid mass becoming extended 

 upon the solid sytem so as to obtain the new figure of equili- 

 brium, should ultimately occupy or envelope this system in 

 the same manner as if the latter had been made to penetrate 

 its interior directly. Under certain circumstances this must 

 occur; but the experiments which are about to be related 

 will show that under other circumstances the result is totally 

 diflferent. 



13. Let us take for the solid system a thin circular plate*, 

 attached by its centre to the iron wire which supports it (PL V. 

 fig. 1), and let us produce the adhesion of its lower surface to the 

 upper part of the mass of oilf. Directly contact is completely 

 established, the oil extends rapidly over the surface presented to 

 it; but, what is remarkable, although the precaution has been 

 taken of rubbing the whole of the system (§ 9), that is the two 

 faces of the plate as well as its rim, with oil, the oil terminates 



* The diameter of that which I have used is 4 centimetres. I mention this 

 diameter for the sake of being definite. It is evident that in our experiments 

 tlie dimensions of the apparatus are completely arbitrar}' ; except that if these 

 dimensions exceed certain limits, the operations will become embarrassing in 

 consequence of the large quantities of liquid which would be required. 



-f- In order that this operation maj' be effected with facility, the sphere of 

 oil must first remain in the surrounding liquid beneath the central aperture in 

 the lid ; the plate being then introduced into the vessel, we have merely to 

 lower it by means of the axis traversing the stopper, to bring it towards the 

 liqtiid mass. If the latter does not occupy the position in question, it must be 

 previouslj- placed there by means of a spatula covered with linen (§ 9). It 

 must be remarked here, tliat true contact between the plaie and the sphere of 

 oil does not usually ensue immediatelj' ; a certain resistance has to be overcome, 

 analogous to that treated of in the note to paragraph 4 of the preceding memoir; 

 but to overcome this, the liquid sphere need only be gently moved by means 

 of the plate. The slight resulting pressure soon causes the rupture of the 

 obstacle and the production of adliesion. 



