26 POPULAR LECTURES AND ADDRESSES. 



known, the problem of describing the three 

 spherical surfaces is clearly determinate. It is 

 an interesting enough geometrical problem. 



If we now for a moment leave our gravitation- 

 less laboratory, and, returning to the Theatre of 

 the Royal 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, see page 27) ; 

 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, 

 arid we shall find that a very slight vertical dis- 

 turbance serves to submerge the mass of bisulphide 

 of carbon. There now it has sunk, and we shall 

 find when its vibrations have ceased that the bi- 

 sulphide of carbon has taken the form of a large 



