612 PLATEAU ON THE PHiENOMENA OF A FREE LIQUID MASS 



requisite for equilibrium ; the thickness of this layer, although 

 very minute absolutely speaking, is undoubtedly, during the first 

 moments, a considerable multiple of the theoretical thickness. If 

 then we produce the layer without extending it to that limit to 

 which it is capable of increasing during the operation, and after- 

 wards leave it to itself, the pressure corresponding to its plane 

 surfaces will still exceed that corresponding to the concave sur- 

 faces of the remainder of the liquid system. Hence it follows 

 that the oil within the layer will be driven towards this other 

 part of the system, and that the thickness of the layer will pro- 

 gressively diminish. The equilibrium of the figure will then be 

 apparent only, and the layer will in reality be the seat of con- 

 tinual movements. The diminution in thickness, however, will 

 be effected slowly, because in so confined a space the movements 

 of the liquid are necessarily restrained ; this is why, as in the 

 experiment in paragraph 17, the mass only acquires its figure 

 of equilibrium slowly, because there is a cause which impedes 

 the movements of the liquid. The thickness of the layer gra- 

 dually approximates to the theoretical value, from which the 

 equilibrium of the system would result ; but unfortunately it 

 always happens that before attaining this point, the layer breaks 

 spontaneously. This effect depends, without doubt, upon the 

 internal movements of which I have spoken above; we can 

 imagine, in fact, that when the layer has become of extreme 

 thinness, the slightest cause is sufficient to determine its rupture. 

 The exact figure which corresponds to the equilibrium is therefore 

 a limit towards which the figure produced tends ; this limit the 

 latter approaches very nearly, and would attain if it were not 

 itself previously destroyed by an extraneous cause. 



Our experiment has led us to modify the results of theory in 

 one particular instance ; but we now see, that, far from weakening 

 the principles of this theory, it furnishes, on the contrary, in- 

 complete as it is, a new and striking verification of it. The con- 

 version of the doubly concave lens into a system comprising a 

 thin layer, is connected with an order of general facts ; we shall 

 see that a large number of our liquid figures become transformed 

 by the gradually produced diminution of the mass of which they 

 are composed into systems consisting of layers, or into the com- 

 position of which layers enter. 



27- If by some modification of our last experiment, we could 

 succeed in obtaining the equilibrium of the liquid system, we 



