1886.] on Capillary Attraction. 491 



for a moment we leave the centre of the earth, and suppose ourselves 

 anywhere else in or on the earth, we find the liquid running up, 

 against gravity, in a thin film over the upper part of the containing 

 vessel, and leaving the interface at an angle of 180^ between the free 

 surface of the liquid, and the surface of the film adhering to the solid 

 above the bounding line of the free liquid surface. This is the case 

 of water contained in a glass vessel, or in contact with a piece of glass 

 of any shape, provided the surface of the glass be very perfectly 

 cleansed. 



When two liquids which do not mingle, that is to say, two liquids 

 of which the interfacial tension is positive, are placed in contact and 

 left to themselves undisturbed by gravity (in our favourite Laboratory 

 in the centre of the earth suppose), after performing vibrations sub- 

 siding in virtue of viscosity, the compound mass will come to rest, in 

 a configuration consisting of two intersecting segments of spherical 

 surfaces constituting the outer boundary of the two portions of liquid, 

 and a third segment of spherical surface through their intersection 

 constituting the interface between the two liquids. These three 

 spherical surfaces meet at the same angles as three balancing forces 

 in a plane whose magnitudes are respectively the surface tensions of 

 the outer surfaces of the two liquids and the tension of their interface. 

 Figs. 2 to 5 (pp. 492, 493) illustrate these configurations in the case of 

 bisulphide of carbon and water for several different proportions of 

 the volumes of the two liquids. (In the figures the dark shading 

 represents water in each case.) When the volume of each liquid is 

 given, and the angles of meeting of the three surfaces are known, 

 the problem of describing the three sj)herical surfaces is clearly 

 determinate. It is an interesting enough geometrical problem. 



If we now for a moment leave our gravitationless laboratory, and, 

 returning to the Theatre of the Eoyal Institution, bring our two 

 masses of liquid into contact, as I now do in this glass bottle, we have 

 the one liquid floating upon the other, and the form assumed by the 

 floating liquid may be learned, for several different cases, from the 

 phenomena exhibited in these bottles and glass beakers, and shown on 

 an enlarged scale in these two diagrams (Figs. 6 to 8, p. 494) ; which 

 represent bisulphide of carbon floating on the surface of sulphate of 

 zinc, and in this case (Fig. 8) the bisulphide of carbon drop is of 

 nearly the maximum size capable of floating. Here is the bottle 

 whose contents are represented in Fig. 8, and we shall find that a 

 very slight vertical disturbance serves to submerge the mass of bi- 

 sulphide of carbon. There now it has sunk, and wo shall find when 

 its vibrations have ceased that the bisulphide of carbon has taken the 

 form of a large sphere supported within the sulphate of zinc. Now, 

 remembering that we are again at the centre of the earth, and that 

 gravity does not hinder us, suppose the glass matter of the bottle 

 suddenly to become liquid sulphate of zinc, this mass would become 

 a compound sphere like the one shown on that diagram (Fig. 3), and 



