244 THE FIGURES OF EQUILIBRIUM OF A LIQUID MASS 



of the surface in question is a surface of revolution. We shall tben see that 

 this same principle is of great importance. AVe may remark here that in the 

 cxporimeut in paragraph 23 the layer commences to appear as soon as the 

 surfaces can no longer constitute spherical segments. Now we shall again find 

 that in the other cases, when a full figure is converted, by the gradual with- 

 drawal of the liquid, into a system composed of layers, or into the composition 

 of which layers enter, the latter begin to be formed when the 

 figure of equilibrium, which the ordinary law of pressures would 

 determine, ceases to be possible. The mass then assumes, or 

 tends to assume, another figure, compatible with a modification 

 of this law. Such is the general principle of the formation of 

 layers under the circumstances in question. 



29. After having formed a converging and a diverging liquid 

 lens, it appeared to me curious to combine these two kinds of lens, 

 so as to form a liquid telescope. For this purpose, 1 first substi- 

 tuted for the ring of iron wire, in paragraph 18, a circular plate 

 of the same diameter, perforated by a large aperture. (Fig. 8.) 

 This plate having been turned in a lathe, 1 was certain of its being 

 perfectly circular, which would be a very difficult condition to fulfil in the case of 

 a simple curved iron wire. In the second place, I took for the solid part of the 

 doubly concave lens a band of about two, centimetres in breaflth, and curved 

 into a cylinder three and a half centimetres in diameter. These two systems 

 were arranged as in I'ig. 9, in such a manner that the entire apparatus being 



f 



Fi^. M 



suspended vertically in the alcoholic mixture by the iron wire a, and the two 

 liquid lenses being formed, their two centres Were at the same height, and ten 

 centimetres distant from each other. In this arrangement the telescope cannot 

 be adjusted by altering the distance between the objective and the eye-piece; 

 but this end is attained by varying the curvatures of these tAvo lenses. With 

 the aid of a few preliminary experiments, I easily managed to obtain an excel- 

 lent Galilean telescope, magnifying distant objects about twice, like a common 

 opera-glass, and giving perfectly distinct images with very little irisation. 

 Fig. 10, which represents a section of the system, shows the two lenses com- 

 bined. 



Figures of equilibrium terminated hy 2}lanc surfaces. 

 Laminar figures of equilibrium. 



Liquid polyJiedra. 



30. In the experiment detailed at paragraph 21, we obtained a figure pre- 

 senting plane surfaces. These were two in number, parallel, and bounded by 

 circular peripheries ; but it is evident that these conditions are not necessary 



