604 PLATEAU ON THE PHENOMENA OK A FREE LlfttJID MASS 



to allow the molecular forces to act ; because the metallic wire, 

 on account of its small extent of surface, would not exert a suf- 

 ficient action upon the superficial layer to cause the liquid to 

 extend so as to adhere to the entire surface of the ring. The 

 mass would then remain traversed by part of the latter, and its 

 spherical form would not be sensibly altered if the metallic wire 

 were small ; the liquid surface would merely be slightly raised 

 upon the wire in the two small spaces at which it issued from 

 the mass. To speak more exactly, under the circumstances in 

 question two figures of equilibrium are possible. One of these 

 differs but very slightly from the sphere ; it is not symmetrical 

 with regard to the ring, one part of which traverses it whilst the 

 other part remains free. The second figure is perfectly symme- 

 trical as regards the ring, and completely embraces its margin ; 

 its surface is composed of two equal spherical curves, the mar- 

 gins of which rest upon the ring ; in other words, it constitutes 

 a true doubly convex lens of equal curvatures. This is the 

 figure which it is our object to obtain. For this purpose, we 

 first give the sphere of oil a diameter slightly greater than 

 that of the metallic ring ; we then introduce the latter into the 

 mass so that it is completely enveloped; lastly, by means of the 

 small glass syringe (§ 9), some of the liquid is gradually removed 

 from the mass*. As this diminishes in volume, its surface is 

 soon applied to every part of the margin of the ring, and the 

 volume continuing to diminish, the lenticular form becomes 

 manifest. Afterwards, by withdrawing more of the liquid, the 

 curvatures of the two surfaces may be reduced to that degree 

 which is considered suitable. In this way a beautiful double 

 convex lens is obtained, which is entirely liquid except at its 

 circumference. Moreover, in consequence of the index of refrac- 

 tion of the olive oil being much greater than that of the alcoholic 

 mixture, the lens in question possesses all the properties of con- 

 verging lenses ; thus, it magnifies objects seen through it, and 

 this magnifying power may be varied at pleasure by removing 

 some of the liquid from, or adding more to, the mass. Our figure 

 therefore realizes that which could not be obtained with glass 

 lenses, i. e. it forms a lens the curvature and magnifying power 

 of which are variable. The diameter of that which 1 formed 

 was 7 centimetres, and the thickness of the metallic wire was 



* The point of tlie instrument is introduced into the vessel through the 

 second aperture in the lid. 



