2 Mr. J. J, Waterstort on Capillarity 



finely dhided into hundredths of an inch, and the reading made 

 with a watchmaker's lens. 



Tube A= rpy^ The numerators express the internal dia- 

 0-Ts7 I ii'ictcrs, the denominators the external 

 Tube B = rrr^r^ diameters in decimals of an inch. 



The tube being firmly fixed in a vertical position, with its 

 lower edge before the centre of the double lens of a photographic 

 camera, an jVi-gand lamp was placed in front, and the focal 

 distance adjusted so that a distinct image of the tube magnified 

 about 40 diameters was thrown back about 30 feet on paper 

 stretched on a vertical board. A small capillary pipette was em- 

 ployed to pass distilled water upon the outer rim of the tube. 

 By inclining the pipette at a greater or less angle, the column 

 of water in the tube and its suspended drop could be increased or 

 diminished at pleasure with the greatest precision. 



Perfectly distinct, highly magnified profiles of the tube and 

 pendent drop were thus obtained at different phases and carefully 

 traced with pencil. The bottom of the cup formed by the upper 

 surface of the liquid was also distinctly marked ; the upper edge 

 less distinctly, but the versed sine of the cup seemed constant 

 under all circumstances, and was assumed to be so. 



While the suspended volume was increased from the smallest 

 beginning, the upper surface within the tube ascended to a cer- 

 tain maximum height, while the lower surface swelled out to the 

 extent of about one-third the external diameter of the tube below 

 the lower rim. The top surface then descended, and also the 

 lower surface, in an increasing ratio until a certain maximum 

 depression was attained, when the lower drop broke ofi".' 



The cycle of this action included first a rise, and then a fall of 

 the centre of gravity of the liquid, and a contemporaneous closing 

 and expanding of the liquid surface. The interior of the tube, 

 being wet, is taken as liquid surface augmented when denuded by 

 the descent of the column, and as liquid surface diminished when 

 covci'cd by the ascent of the column. 



The question proposed for solution was, — Is the ratio between 

 the amount of work performed (as measured by the descent of 

 the centre of gra\ ity) and the amount of hquid surface developed 

 or denuded, a constant ratio ; and if so, to ascertain its numerical 

 value, taking the inch as the standard unit of magnitude ? 



The liquid volume suspended by the capillary attraction being 

 assumed to be enclosed within the surface of revolution defined 

 by the magnified profile, it was easy by an obvious process of 

 graphical integration to compute for each of the several contours 

 delineated, — 1st, the position of the centre of gravity in the ver- 

 tical aitis; 2ndly, the volume of liquid suspended J andSrdly, the 



