WITHDRAWN FROM THE ACTION OF GRAVITY. 611 



either of the surfaces of an extremely thin plane layer will 

 therefore be less than P. Moreover, this pressure will be less 

 in proportion as the layer is thinner, and it may thus diminish 

 indefinitely ; for it is clear that it would be reduced to zero if we 

 supposed that the thickness of the layer was equal to no more 

 than that of a simple molecule. 



We can obtain liquid layers with curved surfaces ; soap-bub- 

 bles furnish an example of these, and we shall meet with others 

 in the progress of this investigation. Now by supposing the 

 thickness of such a layer to be less than twice the radius of the mo- 

 lecular attraction, we should thus evidently arrive at the conclu- 

 sion, that the corresponding pressures at either of its two surfaces 

 would be inferior in intensity to those given by paragraph 4, 

 and that moreover these intensities are less in proportion as the 

 layer is smaller. We thus arrive at the following new prin- 

 ciple : — 



In the case of every liquid layer, the thickness oftvhich is less 

 than twice the radius of the sphere of activity of the molecular 

 attraction, the pressure will not depend solely upon the curvatures 

 of the surfaces, but will vary with the thickness of the layer. 



25. We thus see that an extremely thin plane liquid layer, 

 adhering by its edge to a thick mass the surfaces of which are 

 concave, may form with this mass a system in a state of equili- 

 brium ; for we may always suppose the thickness of the layer to 

 be of such value, that the pressure corresponding to the plane 

 surfaces of this layer is equal to that corresponding to the con- 

 cave surfaces of the thick mass. Such a system is also very re- 

 markable in respect to its form, inasmuch as surfaces of different 

 nature, as concave and plane surfaces, succeed each other. This 

 heterogeneity of form is moreover a natural consequence of the 

 change which the law of pressures undergoes in passing from 

 the thick to the thin part. 



26. As we have already seen, theory demonstrates the possi- 

 bility of the existence of such a system in a state of equilibrium. 

 As regards the experiment which has led us to these considera- 

 tions, although the result presented by it tends to realize in an 

 absolute manner the theoretical result, there is one circumstance 

 which is unfavourable to the completion of this realization. We 

 can understand that the relative mobility of the molecules of 

 oil is not sufficiently great to occasion the immediate forma- 

 tion of the liquid layer with that excessive tenuity which is 



