608 PLATEAU ON THE PHiENOMENA OF A FREE LIQUID MASS 



of gravity, by the phaenomenon of the elevation of a liquid 

 column in a capillary tube, the walls of which are moistened 

 by it. 



Reasoning upon these facts, as we have done at the end 

 of paragraph IJ in regard to convex surfaces of spherical 

 curvature, we shall arrive at the conclusion that the entire 

 pressure exerted by a concave superficial layer of spherical 

 curvature is the result of minute individual pressures arising, 

 from all the elements of this layer, and that the intensity of each 

 of these minute pressures depends upon the curvature of that 

 element of the layer from which it emanates. Our last experi- 

 ment therefore perfectly verifies that parff of the theory which 

 relates to plane and convex surfaces of spherical curvature. 

 Lastly, in the state of equilibrium of our liquid figure, the curva- 

 ture being the same at all points of each of the two concave sur- 

 faces, it is again evident that all the minute elementary pressures 

 are equal to each other, which gives a new complete verification 

 of the general condition of equilibrium. 



22. The figure we have just obtained constitutes a biconcave 

 lens of equal curvatures, and possesses all the properties of 

 diverging lenses, i. e. it diminishes objects seen through it, &c. 

 Moreover, as the curvature of the two surfaces may be increased 

 or diminished by as small degrees as is wished, it follows that 

 we thus obtain a diverging lens, the curvature and action of which 

 are variable. 



23. Now let us suppose that we have increased the curva- 

 tures of the lens until the two surfaces nearly touch each other 

 by their summits*. We might presume, that if the removal 

 of the liquid were continued, the mass would become dis- 

 united at that point at which this contact took place, and that 

 the oil would recede in every direction towards the metallic 

 band. This is however not the case ; we then observe in the 

 centre of the figure the formation of a small sharply-defined 

 circular space, through which objects no longer appear dimi- 

 nished, and we easily recognize that this minute space is occu- 

 pied by a layer of oil with plane faces. If the removal of the 

 liquid be gradually continued, this layer inci'eases more and 



* To effect this operation, the point of the syringe must not be placed in the 

 middle of the figure, as in the case of the doubly-convex lens ; but, on the con- 

 trary, near the metallic band, as this is now the point where the greatest thick- 

 ness of the liquid exists. 



