

CONSTRUCTION OF APPARATUS. 167 



s the pressure upon the base, diminished by the upward 

 )ressure of the liquid against the sides, which tends to 

 ift the sides from the bottom of the vessel. If therefore 

 he pressure of the liquid upon the base, diminished by 

 lie upward pressure, is still equal to the weight of the 

 iquid, it follows that, in a vessel which becomes yra- 

 lually wider towards the base, the pressure upon the bottom 

 's greater than the weight of the contained liquid* 



For experiments on the pressure of liquids vessels with a moveable 

 >ottom are required. They may be prepared from lamp cylinders 

 he glass of which is not too thin. In such a cylinder, fig. 117 A, 

 hree rather deep notches a, &, c, running all round, are made with the 

 hree-cornered file ; a burning pastille is held at a point of the notch 



7? 



FIG. H7(| real size). 



crack is produced, which is then carried all round. In a 

 econd cylinder, fig. 117 B, the notch is only made all round at a, 

 yhile at & only a short notch is made at the edge, and the crack 

 arried along the line indicated, and from c to c all round the 

 ylinder. This is necessary because it is scarcely possible to carry a 

 rack in a direct line all round c c, so near to the place where the 

 ylinder becomes narrower. The cylinders marked 1, 2, 3, are to 

 e well ground at one end 1 at a, 2 at c, 3 at c c, so as to fit closely 

 fhen placed upon the plates used for the experiments on adhesion 

 he one marked 4 must be carefully ground well at both ends. Select 

 piece of window or plate glass, as even as possible, place it horizontal 

 nd grind with emery and a little water, moving the cylinder round 

 i a small circle and turning them at the same time. Begin with rough 

 mery and use about three sorts, ending with the finest. This will 

 e quite sufficient to prevent the escape of water, if the cleaned 

 dge of the cylinder is placed upon the adhesion plate, and the 



