Chap. 6.]

Variety of their forms and materiah.

515

it than over the other. Nor does the effect depend upon any differencein the actual lengths of the legs, for they are often in this respect thesame ; and sometimes the receiving one is much longer (in an obliquedirection) than the other—not yet does their comparative diameters con-tribute to the results ; for the short one may be much more capaciousthan the long one. It is the difference in the perpendicular length of theliquid columns within the legs that causes a siphon to act: the column in thedischarging leg must exceed in this respect that containedin the receiving one, or no action can take place. Byexamining the figure in the naargin, it will be perceivedthat the column in the receiving leg extends only from thesurface of the liquid in the vessel to the bend, whereas inthe other it extends from the bend to the orifice. As thepressure of fluids is as their depth without regard to theirvolume, the hydrostatic equilibrium of the two columns isdestroyed, when the longer one necessarily preponderates,upon which the vacuity left in the upper part of the tu’beis filled, by the a-tmosphere driving fresh portions up theother leg.

But siphons could not act at all were it not for thatproperty of fluids by which their particles ding to each other. The tena-city of liquids may be considered like that of solids, only less intense;and thus it is when water flows through a siphon, the descending particlesactually drag down those, above them, somewhat like a chain or ropeunequally suspended over a pulley, when the longer end pulls the shorterone after it. A siphon is in fact a contrivance by which liquid chains orropes are thus made to act. But for the cohesion of liquids the Contentsof the discharging leg would drop out like sand, and no further effectwould follow—the rope would be broken, and the separated parts fallasunder. The influence of cohesion in the action of siphons is proved bythe fact that very short ones continue to operate when removed into avacuum. &

The tenacity, or what might almost be called the malleability of liquids,is beautifully exemplified in soap bubbles. These yield to impressionswithoUt breaking. They fall on and rebound from the floor like bladdersor balls of india rubber. They shake in the wind, and their figures be-come altered like that of balloons tossed to and fro in the air : all this theyoften endure before their shells are broken by evaporation.

Siphons are exceedingly diversified in their forms, materials and uses.They are made of cylindrieal and other shaped tubes, and both of uniformand irregulär bore. The legs of some are parallel, while in others theymeet at every angle—sometimes straight and often crooked—one may belarger than the other, or both may be alike ; they also may be separate,one loosely slipping into or over the other. Instead of tubes siphons aresometimes formed by an arrangement of plates, and also by a combinationof vases. This plastic property has occasioned their concealment in morevarious forms than Proteus ever assumed. Siphons are made of tin, cop-per, iron, silver, glass, lead, earthenware, leather, wood, canes; and(capillary ones) of paper, Strips of cloth, threads of cotton, &c. Examplesof their various form* and applications Will be found noticed in the follow-ing historical sketch.

The origin of siphons like that of pumps is lost in antiquity. Some

a For Information on the aetion of siphons in vacuo, see Boyle’s Works, by Shaw,vol. ii, 446. History and Memoirs of the French Academy, translated by Martin andChambers, vol. iv. 374 ; and Desaguliers f>xp er. Philos. vol. ii. 168. •

No. 234.