WITHDRAWN FROM THE ACTION OF GRAVITY. 245 



in order to allow plane surfaces to belong to a liquid mass in equilibrium. We 

 can understand that the forms of the solid contours might be indifferent, pro- 

 vided they constitute plane figures. We can, moreover, understand that the 

 number and the relative directions of the plane surfaces may be a matter of 

 indifference, because these circumstances exert no influence upon the pressures 

 which correspond to these surfaces, pressures which will always remain equal 

 to each other. Lastly, it follows from the principle at which we arrived at the 

 end of paragraph 20, relative to the influence of solid wires, that for the estab- 

 lishment of the transition between a plane and any other surface, a metallic 

 thread representing the edge of the angle of intersection of these two surfaces 

 will be sufficient. We are thus led to the curious result, that we ought to be 

 able to form polyhedra, which are entirely liquid excepting at their edges. 

 Now, this is completely verified by experiment. If for the solid system we 

 take a framework of iron wire representing all the edges of any polyhedron, 

 and we cause a mass of oil of the proper volume to adhere to this framework, 

 we obtain, in fact, in a perfect manner, the polyhedron in question ; and the 

 curious spectacle is thus obtained of parallelopipedons, prisms, &c., composed 

 of oil, and the only solid part of which is their edges. 



To produce the adhesion of the liquid mass to the entire framework, a 

 volume is first given to the mass slightly larger than that of the polyhedron 

 which it is to form ; it is then placed in the framework ; and, lastly, by means 

 of the iron spatula, (§ 9,) which must be introduced by the second aperture of 

 the lid of the vessel, and which is made to penetrate the mass, the latter is 

 readily made to attach itself successively to the entire length of each of the 

 solid edges. The excess of oil is then gradually removed with the syringe, 

 and all the surfaces thus become simultaneously exactly plane. But that this 

 end may be attained in a complete manner, it is clearly requisite that the 

 equilibrium of density between the oil and the alcoholic mixture should be 

 perfectly established; and the slightest difference in this respect is sufficient to 

 alter the surfaces sensibly. It should also be borne in mind that the manipu- 

 lation with the spatula sometimes occasions the introduc- 

 tion of alcoholic bubbles into the interior of the mass of 

 oil. These are, however, easily removed by means of the 

 syringe. 



31. Now, having formed a polyhedron, let us see what 

 will happen if we gradually remove some of the liquid. 

 Let us take, for instance, the cube, the solid framework of 

 which, with its suspending wire, is represented at Fig. 11.* 

 Let the point of the syringe be applied near the middle of 

 one of the faces, and let a small quantity of the oil be drawn 

 up. All the faces will immediately become depressed simul- 

 taneously and to the same extent, so that the super- 

 ficial square contours will form the bases of six similar hollow figures. We 

 should have imagined this to have been the case for the maintenance of equality 

 between the pressures. 



If fresh portions of the liquid are removed, the faces will become more and 

 more hollowed ; but to understand what happe-ns when this manipulation is 

 continued, we must here enunciate a preliminary proposition. Suppose that a 

 square plate of iron, the sides of which are of the same length as the edges of 

 the metallic frame, is introduced into the vessel, and that a mass of oil equal 

 in volume to that which is lost by one of the faces of the cube is placed in con- 

 tact with one of the faces of this plate; I say that the liquid, after having 

 become extended upon the plate, will present in relief the same figure as the 



* The edges of all the frames which I used were 7 centimetres in length. 



