1158

THEORY AND PRACTICE OF ENGINEERING.

Book II.

and its limits are the minimum and maximum pressures which correspond to the twoheights to which the water can elevate itself in the tube K L, at the beginning and end ofthe movement.

When the vessel C’’ is empty the cock Z is closed ; the vessel C is then emptied by thepipe V X, which is closed by a plug, X, removable at pleasure; the vessels C, C /f are filledas before stated, and the machine is ready to play again.

The tube B D', by which the water falls from C to C" might terminate at P ; the pres-sure of the air of the vessel C 7 would then only depend on the height of the level N Iabove the point P ; as long as the tube B D is prolonged to D, this pressure depends on thedistance between the two variable levels, X I and 11 S.

Supposing that instead of filling the vessels C and C" with water, some other liquid weresubstituted, as mercury, and the air which the vessel C 7 and the tube F II contain replacedby another incompressible fluid, such as water, the pressure of the water would replace thatof the air, and the mercury in the vessel C produce in falling a force capable of elevatingthat in the vessel C" in the tube K L. The incompressibility of water transmits the movingpower, by increasing the effect for the power employed to compress the air which wouldremain in the vessel C, and which is gained the instant that the tube K L no longer containswater, as the air compressed in the vessel C 7 mixes with the atmospheric air by the tubeK L, and produces no useful effect.

The invention of this machine is attributed to Iliero, who lived 100 years b.c., and itha* been constructed on a large scale for emptying water from the mines at Schemnitz inHungary ; its principle, modified by Gerard, has been applied to elevate the oil inhydrostatic lamps. In the machine of Detranville, water is raised by the rarefaction of theair; in the fountain of Iliero the same effect is produced by condensing it.

Gerard’s have this advantage over the ordinary Argand lamps, that the reservoir of oilbeing below the focus of the lamp, it does not throw a shadow on the surrounding objects.

Fig. 1757. represents the new fountain of Iliero as applied to hydrostatic lamps : pq Eis a vessel filled with oil, which falls through a tube 13 D Y in the vessel It 1) S, which is thenfull of aii ; these two vessels correspond with those marked C and C' in fig. 1756. : they aredesignated by the same letters in fig. 1757. : the vessel C only communicates with the externalair by the tube U T, which traverses the cover pq ; the oil cannot escape from the vessel bythe tube 13 D Y, except when the air enters by the tube T U, so that the elastic force of theair, pq N I, and the pressure of the liquid, N I U, always equalise the pressure of the atmo-spheric air which fills the tube U T.

Drinking glasses for birds and inkstands are constructed on this principle of equilibrium.The tube 131) Y is plunged below Y into a cylindrical vessel 5« filled with oil and openabove, while it is closed below by' the plug Y ; the height from which the oil of the vesselC falls into C" is constant and equal, 13 Y, whatever may be the heights of the level N I andR S in C and C'.

The vessel C 7 communicates with another, C", full of a liquid similar to that in C 7 ; thiscommunication is established by means of a tube of any form FEell, which passes throughthe cover P Q of the vessel C 77 , terminating at the bottom II of this vessel. The vessel C 7communicates with the external air by a tube L K, which is prolonged to the bottom of thevessel; the orifices H and K of these two tubes arc in the same line with the level II K.

If we suppose the vessel P pq Q or C 7/ of a height P p less than 13 Y, the pressure of thefluid PII Q on the orifice II cannot equalise the air contained in the vessel C 7 and in thetube Fell ; this air being compressed by the weight of the atmosphere and a column ofliquid of the height By, it will leave the tube F E II by the orifice II, and occupy a spaceP Q/it in the upper part of the vessel Vpq Qor C 77 ; the liquid which the air has replaced willelevate itself in the tube K L.

"When the air contained in the vessels C', C 77 is in equilibrio, the height KL, to whichthe liquid will elevate itself, will be equal to the constant keight 13y .• the pressure on theextremities K and H of the tubes UL and II c E F are equal; that at II results from thepressure of the liquid n i H, and the elastic force of the air contained in the vessel C and thetube Fell; but this elastic force has for its measure the height BY of the liquid; thepressure at the extremity of the tube L K is due to the same height B Y, and by giving toKLa height less than B Y, the liquid of the vessel C' would rise in the tube K L by aconstant force of pressure.

In the hypothesis of the ascensional movement of the air contained in the vessel C 7 andthe tube FII, the air of this tube is less compressed at II than at F, otherwise theascensional movement would be impossible; but to fulfil the object proposed it sufficesthat the compression of the air at II be constant: by giving to the tube FII convenientform and dimensions, the vessel C 77 may be placed in any position with regard to the ves-sel C.

AY hen the vessels C and C 7/ are empty, there are several methods of refilling them :fig. 1757. indicates the following; the tube K L is composed of two parts, K /, JL, whichare screwed together at til; when they are separated the oil is poured through the opening 4