592 PLATEAU ON THE PIKISNOMENA OF A FREE LIQUID MASS 



liquid upon itself emanate solely from an excessively thin super- 

 ficial la3'er. We shall denominate this consequence the prin- 

 ciple of the superficial layer. 



7' A spherical surface evidently satisfies the condition of equi- 

 librium, because all the curvatures in it are the same at each 

 point ; also when our mass is perfectly free, i. e. when it is not 

 adherent to any solid Avhich obliges its surface to assume some 

 other curve, it in fact takes the form of the sphere, as shown in 

 the preceding memoir. oi uomo : 



8. Before proceeding further, we ought to elucidate one point 

 of great importance in regard to the experimental part of our 

 investigations. The liquid mass in our experiments being im- 

 mersed in another liquid, the question may be asked whether 

 the molecular actions exerted by the latter exert no influence 

 upon the figure produced, or, in other words, whether the figure 

 of equilibrium of a liquid mass adherent to a solid system, and 

 withdrawn from the action of gravity by its immersion in another 

 liquid of the same density as itself, is exactly the same as if the 

 mass adherent to the solid system were really deprived of 

 gravitj' and were placed in vacuo. Now we shall show that this 

 really is the case. The molecvdar actions resulting from the 

 presence of the surrounding liquid are of two kinds, viz. those 

 resulting from the attraction of this liquid for itself, and those 

 resulting from the mutual attraction of the two liquids. Let us 

 first consider the former, imagining for an instant that the others 

 do not exist. The surrounding hquid being applied to the free 

 surface of the immersed mass, the former presents in intaglio the 

 same figure as the latter mass presents in relief. Those molecules 

 of this same liquid which are near the common surface of the two 

 media must then exert pressures of the same nature as those 

 which we have considered throughout the preceding details, 

 towards the interior of the liquid to which they belong, and 

 these pressures must consequently also impart a figure of equi- 

 librium to the surface in iiitaglio ; so that if the immersed mass 

 of itself had no tendency to assume any one figure rather than 

 another, the surrounding liquid would give it a determinate one, 

 by compelling it to mould itself in the above hollow figure. 

 Tliis is why a bubble of air in a liquid assumes the globular form, 

 solely in consequence of the pressures exerted by the liquid upon 

 it. -Now let us suppose that the immersed mass has assumed 

 that figure which it would acquire in vacuo if really deprived of 



