364 



Mr. A. M. Worthington. 



[June 16, 



show the manner in which the form of the surface alters with the 

 growth of the drop. 



The instability of the figure close to the point of rapture makes it 

 difficult to trace the outline correctly quite to that point. 



The short horizontal line below the drop shows the maximum depth 

 attained before rupture, and the area enclosed by the last outline that 

 could be drawn correctly, and the one which is nearest the limit of 

 stability is shaded for the sake of distinctness. The dotted outline, 

 generally the innermost, shows the amount of liquid which remained 

 adhering to the tube after the separation of the lower portion. 



It may be worth while to mention here that where the liquid wets 

 the whole of the base of the tube the form and dimensions of the out- 

 line were found to depend on the external and not at all on the 

 internal diameter of the tube. 



One of the first points that strikes anyone inspecting these figures 

 is, that the maximum depth attained varies surprisingly little with the 

 diameter of the tube. 



An early series of observations on this point made with insufficient 

 magnification showed so slight a variation that I was led to suppose 

 that the maximum depth might really be constant and independent of 

 the size of the tube, and to seek for an empirical formula involving 

 only the physical constants of the liquid to express this depth.* 



Greater magnification, however, shows that this is not the case ; that 

 the maximum depth diminishes on the whole with the size of the tube, 

 but is rather less in a drop pendent from a plane surface of indefinite 

 extent than in one hanging from a tube just narrow enough for the 

 drop to attach itself at the edge. 



Another point that attracts immediate attention is, that whereas 

 the form of drops of different liquids hanging from the same tubes 

 differs materially (compare, for example, water and turpentine), yet 

 drops of (say) turpentine hanging from narrow tubes are similar in 

 form to water drops hanging from wider tubes. 



That this would be the case has been already shown from theoretical 

 considerations by M. Dupre,f who has also pointed out the ratio be- 

 tween the diameters of the tubes that corresponds to complete simi- 

 larity of the drop form for two different liquids. 



* A very close approximation is given by the formula — 



Maximum depth =$7r a / ensiQn , 

 V density 



which was suggested by the equation to the generating curve, 

 f " Theorie Mecanique de la Chaleur," p. 329. 



The following method of finding the ratio of tube-diameters, necessary for the 

 symmetry of drops of different liquids, being rather simpler in form than that given 

 by M. Dupre, may be welcome to some readers. 



