238 THE FIGURES OF EQUILIBRimi OF A LIQUID MASS 



18. The principle of the puperficial layer, applied to the preceding experi- 

 ment, allows of the latter being modified in such a manner as to obtain a very 

 remarkable result. When the figure of equilibrium is once attained, the per- 

 forated i)late acts upon the superficial layer by its external border only. The 

 whole of the remainder of this plate then exerts no influence upon the figure in 

 question. Hence it follows that this figure would still be the same if the aper- 

 ture were enlarged, only the greater the diameter of the latter the less time is 

 required for the establishment of the equality between the two cur^■atures. 

 Lastly, we ought to be able to enlarge the ajjcrture nearly to the margin of the 

 plate without changing the figure of equilibrium ; or, in other words, to reduce 

 the solid system to a simple ring of thin iron wire. Now, this if? confirmed by 

 experiment; but, to put it in execution, we cannot confine ourselves, as before, 

 to making the solid system penetrate a sphere of oil of less diameter than that 

 of this same system, and subsequently to allow the molecular forces to act, be- 

 cause the metallic wire, on account of its small extent of surface, Avould not 

 exert a sufficient action upon the supc^rficial 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 Avhich 

 traverses it whilst the other part remains free. The second figure is perfectly 

 symmetrical as regards the ring, and completely embraces its margin; its surface 

 is composed of two equal spherical curves, the margins of wdiich rest upon the 

 ring; in other words, it constitutes a true doubly convex lens of equal curva- 

 tures. 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 com- 

 pletely enveloped; lastly, by means of the small glass syringe, (§ 9,) some of 

 the liquid is gradually i-emoved from the mass.* As this diminishes in A-olume, 

 its surface is soon applied to every part of the margin of the ring, and the 

 volume continuing to diminish, the lenticular form beeomes manifest. After- 

 wards, by withdrawing more of the liquid, the curvatures of the two surfaces 

 may be reduced to that degree which is considered suitable. In this Avay a 

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

 circumference. Moreover, in consequence of the index of refraction of the 

 olive oil being much greater than that of the alcoholic mixture, the lens in 

 question posfiesscs all the properties of converging lenses ; thus, it magnil^es 

 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 I formed was 7 centimetres, and the thickness of the 

 metallic wire was about ^ a millimetre. A much finer ware might have been 

 used with the same success ; but the apparatus Avould then become inconve- 

 nient on account of the facility with which it would be put out of shape. By 

 operating with care, the curvatures of the lens may be diminished so as almost 

 to make them vanish ; thus I have been enabled to reduce the lens which I 

 formed, and the diameter of which, as I have stated, Avas 7 centimetres, to 

 such an extent that it was only 2 or 3 millimetres in thickness. Hence Ave 

 might presume that it would be possible to obtain, by a proper mode of pro- 



* The poiut of the inslrumcut is iutroduccd into the vessel throutrli the second aperture in 

 tbo lid. <= i 



