642 PLATEAU ON THE PH.ENOMENA OF A FREE LIQUID MASS 



to be observed. As the amalgamation of the copper wires 

 always extends slightly upon their convex surface, the latter 

 is coated with varnish, so that the amalgamation only occurs 

 upon the small plane section. It would be almost impossible 

 to judge by simple inspection of the exact point at which the 

 separation of the copper wires from each other, to allow of the 

 liqviid attaining a cylindrical form, should be discontinued. To 

 avoid this difficulty, the length of the cylinder is given before- 

 hand, and this length is marked by two faint scratches upon 

 the lateral surface of one of the strips of glass ; the weight of 

 the globule of mercury, which is to form a cylinder of this 

 diameter and of the length required, is then determined by cal- 

 culation from the known diameter of the wire ; lastly, by means 

 of a delicate balance, the globule to be used in the experiment 

 is made exactly of this weight. All that then remains to be 

 done, is to extend the little mass until the extremities of the 

 copper wires between which it is included have reached the marks 

 traced upon the glass. Lastly, in making a series of experi- 

 ments, the same mercury may be used several times if the iso- 

 lated spheres are united into a single mass at the end of each 

 observation. However, after a certain number of experiments, 

 the mercury appears to lose its fluidity, and the mass always 

 becomes disunited at some point, in spite of all possible precau- 

 tions, before it has become extended to the desired length, 

 which phaenomena arise from the solid wires imparting a small 

 quantity of copper to the mercuiy. The latter must then be 

 removed, the plates of glass and the strips cleaned, and a new 

 globule taken. The amalgamation of the wires also sometimes 

 requires to be renewed. 



52. By means of the above apparatus and methods, I have 

 made a series of experiments upon the transformation of the 

 cylinders ; but before relating the results, it is requisite for their 

 interpretation that we should examine the phaenomenon a little 

 more closely. 



Let us imagine a liquid cylinder of considerable length in pro- 

 portion to its diameter, and attached by its extremities to two 

 solid bases ; let us suppose that it is effecting its transformation, 

 and let us consider the figure at a period of the phaenomenon 

 anterior to the separation of the masses, i. e. when this figure is 

 still composed of dilatations alternating with constrictions. As 

 the surfaces of the dilatations pi-oject externally from the primitive 



