HYDRODYNAMICS. 



485 



cml ir-tru- 

 I *5"*Jf a 



,-j 



is half immersed, and since it has half the specific gra- 

 vity of the fluid, the semicylinder is in the same cir- 

 cumstance as if it were floating, and therefore exerts no 

 pressure on the horizontal axis C. As the vessel is 

 emptied either by evaporation, or by discharge from an 

 orifice, the quantity of the semicylinder immersed will 

 be diminished, and the equilibrium of consequence 

 destroyed ; and it will therefore move round the axis 

 C till half of it is again immersed, and the equilibrium 

 restored. In this way the semicylinder will always de- 

 scend as the water runs out, and consequently the fluid 

 rily stand at the same height AB in the 



10. Experiment! illustrative of the Pretntre of the Supe- 

 rior Strata of Fluid* upon the Inferior Strata. 



F.r.-:- 



Exp. I. If we pour coloured water into a glass TCS- 



*' **"* P ut * tube ^ ?'***' w ' th * bore exce *d' n K *V 

 J> prtKurt of an '"eh, the coloured water will stand in the tube at 

 of the nipe- the same height as it does in the vessel. Let oil of 

 ri*r*nt*of turpentine be now poured above the water, and its 

 9 preure upon the surface of the water will cause the 

 coloured fluid to ascend in the tube, but always to a 

 height less than that of the surface of the oil of turpen- 

 tine; the column of the colon red fluid raised, being to the 

 thickness of the mass of oil in the inverse ratio of their 

 specific gravities. The same experiment may be made 

 by substituting quicksilver in place of the coloured 

 water, and water in place of the oil of turpentine. 



Exp. 9. If a vessel contains any fluid, a heavier fluid 

 may be introduced below the lighter one, without any 

 admixture taking place, and their separating surface will 

 be horizontal. If a vessel for example contains water, 

 let a quantity of milk be drawn up into a glass tube by 

 suction, and if the open end of the tube is placed at the 

 bottom of the vessel, and the milk allowed to discharge 

 itself gradually, it will occupy the lower part of the 

 vessel. 



11. Dttcription of the Hydreole* invented by M. Man- 

 Htmry Drctot. 



''''* In Prop. I. of Chap. I. Sect. II. it has 



trated, that when two fluids are placed in the opposite 

 ' branches of a bent glass tube or syphon, the altitudes 

 4. M*D- above the point of junction will be in the inverse ratio 

 KT De- of their specific gravities; that is, a fluid lighter than 

 water will rise to a greater height in one of the branches 

 than the water in the other. 



M. Mannoury Dectot ha* employed this principle 

 very ingeniously in raising water above its natural 

 level, by mixing air with the water, so as to diminish 

 its specific gravity, and thus cause it to rise to a con- 

 siderable height in one of the branches of the syphon. 

 In order to make an intimate mixture of water and air, 

 he introduces the air in the form of minute babbles, 

 which lodge among the molecules of the water, and 

 being kept separate from each other, they are retained by 

 dhriion hi such a manner that they are only disen- 

 gaged slowly, and do not unite with each other and 

 escape until the water which contains them has been 

 raited to the proper height. 



M. Mannoury Dectot has given two forms to this 

 machine, one of which he calls the hydreole by suction, 



Hydrottati- 

 cat Instru- 

 ments and 



Kxpcri- 



nicnts. 



Hydreole 

 by pressure. 

 PLATE 

 CCCXIIL 

 Fig. 11. 



and therefore it will rise to a greater height than the 

 reservoir from which it flows. 



In the hydreole by pressure, the air is driven by force 

 through a number of small holes, so as to mix itself 

 with the water in a number of minute bubbles. In or- 

 der to form a proper idea of this machine, let us sup- 

 pose that ABCD, Plate CCCXIIL Fig. 1 1. isa reservoir 

 filled with water, and that the bent tube abed is join- 

 ed to it at D. The water will obviously rise to the same 

 level ab, AB in both vessels. Let us suppose, that a 

 pair of bellows M is applied to an opening N in the 

 tube, closed with a plate of iron, perforated with a great 

 number of small holes, the air discharged from the bel- 

 lows will enter the water in the form of very minute 

 bubbles, which will be kept separate from each other by 

 the mutual adhesion of the particles of water. The wa- 

 ter above X will thus be rendered specifically lighter, and 

 will therefore rise in the tube abed. Instead of using 

 a pair of bellows, M. Mannoury Dectot obtains a current 

 of air in the following manner. Between the opening N 

 and the reservoir ABCD, he places a close vessel, com- 

 municating by one pipe with the reservoir, and by ano- 

 ther with the opening at N. A column of water from 

 the reservoir runs into the close chamber, compresses 

 the included air, and thiscompressed air rushing through 

 the other tube, enters through the holes in the aperture 

 at N, and mixes itself with the water to be raised. 



We have not keen able to obtain any account of the 

 preceding machine, but the very general one contained 

 in the report of MM. Prony, Perier, and Carnot, which 

 was approved of by the Institute of France, on the 28th 

 December 1812. An account of M. Mannoury Dectot's 

 new hydraulic machines, will be found in Part HI. of 

 this article on HYDRAULIC MACHINERY. 



IS. Dttcription of the Common Syphon. 



The syphon is a tube of glass or metal, bent in such Description 

 a manner that one of its legs or branches is longer than <* lb J- 

 the other. It is represented in Fig. 10. by ABCD. P^j. 

 The shorter leg AB is immersed in the fluid in the ves- cccxvii. 

 sel MNOP, and by applying the mouth to the orifice Fig. 10. 

 D, and sucking out the air in the syphon, the water as- 

 cends, and will continue to be discharged at D till the 

 vessel is completely emptied. 



Let us suppose that the syphon had legs of equal 

 length, such aa AB, BC, and that the water was drawn 

 up by suction till it reached the extremity C ; then it 

 is obvious, that aa the pressure of the air on the surface 

 of water is equal to the pressure of the air at the extre- 

 mityC, and as the columns A B,BC of the fluid arc equal, 

 there is no force which could enable the water to dis- 

 charge it.-* If at C. When the leg BC, however, is length, 

 ened, so M to be equal to BD, then the water is dis- 

 charged at D by the pressure of the additional column 

 CD, anil the velocity with which it is discharged will 

 be in proportion to the difference between the legs of 

 the syphon. 



13. Description of an Improved Syphon. 



The improved syphon is shewn in Fig. 11. where D Demiptioa 

 p-cock fixed at the ex 



and the other the hydreole by pressure. In the hydrr- 

 ole by suction, the water paste* through a n 

 absorbs part of it, and becomes in MOM mCMV 



is a stop-cock fixed at the extremity of its longer branch of *"! m " 

 AB. A small bent tube ED lying along the outside *?** 

 of the same branch, communicates with the cavity (., n_ 

 of air, of the branch AB, above the stop-cock. When the 

 iseou*, aperture C is placed in the fluid to be drawn off, the 



