1881.] On Pendent Drops. 363 



raised or lowered by a rack and pinion-screw, so as to serve as a 

 perfectly air-tight piston. 



Fig. 1. 



By means of an Argand lamp, F, whose light is condensed by the 

 lens Gf, a magnified image of the end of the tnbe is thrown by the 

 lens H, npon a piece of white paper, I, fixed on the wall of the room 

 near the syringe. 



K is a plate-glass cell filled with water to keep off the heat of the 

 lamp. 



A snpply of the liquid to be observed is drawn up into the bulb or 

 wide tube B, by means of the syringe, or more conveniently by means 

 of an india-rubber bulb, L, interposed for the purpose between B and 

 D. 



The tube A is then carefully wiped on the outside with a clean 

 linen cloth, and the observer standing by the paper gradually expels 

 the liquid by raising the mercury cup, and a drop is extruded which 

 wets the whole of the bottom of the tube, the outline of which he 

 traces on the white paper with a finely-pointed lead pencil, at any 

 stage of which he desires a record, up to the point of rapture. 



This tracing affords all the information necessary for calculating* 

 the value of the surface tension, the amount of magnification being 

 known from the ratio of the diameter of the tube to that of its image 

 on the screen. 



As the first few drops expelled are apt not to wet the whole of 

 the base of the tube thoroughly, and therefore to be rather smaller 

 than those which follow, it is well to let one or two fall off before 

 taking a tracing if a series of outlines at different stages is required. 



The tube A can be exchanged at pleasure for others of different 

 diameters, and when it is wished to observe the form of a drop of one 

 liquid pendent in another, the latter is placed in a plate-glass cell with 

 parallel sides, and the tube A dips into it. 



The figures of the Plate are tracings (reduced one-half) obtained in 

 this way with different liquids and tubes of various diameters, and 



vol. xxxit. 2 c 



