1886.] 



Capillary Attraction. 



499 



do not represent real capillary surfaces — but these mathematical 

 extensions of the problem, while most interesting and instructive, are 

 such as cannot be adequately treated in the time now at my disposal. 

 In these other diagrams, however (Figs. 13 to 28), we have 

 certain portions of the curves taken to represent real capillary 

 surfaces shown in section. In Fig. 13 a solid sphere is shown in 

 four different positions in contact with a mercury surface ; and again, 

 in Fig. 14 we have a section of the form assumed by mercury resting 



Fig. 13. 



Mercury in contact with solid spheres (say of glass). 



Fig. 14. 



Sectional view of circular V-groove containin 



g mercury. 



in a circular V-groove. Figs. 15 to 28 (pp. 500-502) show water- 

 surfaces under different conditions as to capillarity ; the scale of the 

 drawings for each set of figures is shown by a line the length of 

 which represents 1 centimetre ; the dotted horizontal lines indicate 

 the positions of the free water-level. The drawings are sufficiently 

 explicit to require no further reference here save the remark that 

 water is represented by the lighter shading, and solid by the darker. 



We have been thinking of our pieces of rigidified water as be- 

 coming suddenly liquefied, and conceiving them inclosed within ideal 

 contractile films ; I have here an arrangement by which I can exhibit 

 on an enlarged scale a pendant drop, inclosed not in an ideal film, 

 but in a real film of thin sheet indiarubber. The apparatus which 

 you see here suspended from the roof is a stout metal ring of 60 

 centimetres diameter, with its a2)erture closed by a sheet of india- 



