508 



HYDRODYNAMICS. 



Hydraulic thick, and containing about 83 cubic feet. Another 

 pipe EKHB, 4 inches in diameter, rises from E, with- 

 m -I inches of the bottom of the vessel KE, is soldered 

 into its top at K, and rises into the reservoir B. The cy- 

 linder KE communicates by a tube with a cock at 11, 

 with the water C to be raised, and has a cock Q at its 

 top. Let us now suppose that the cock M is shut, and 

 all the other cocks open. The cylinder TD will contain 

 air, and KE will contain water standing as high as the 

 level of the water in the cistern C. Shut the cocks'N, P, 

 Q, and R, and open the cock M. The water from A 

 will descend into the vessel TD, and after it rises above 

 the mouth 13 of the pipe, it will compress the air in 

 the vessel TD, in the pipe TOG, and in the upper 

 part of the vessel KE. The action of this air upon 

 the water in KE will force it up the pipe KH, till it is 

 discharged into the reservoir B. This discharge into 

 B goes on till the upper vessel TD is filled with water. 

 As soon as this happens, the water is prevented from 

 running into the pipe TO by a cork ball, or double 

 cone, which hangs in the pipe TO by a brass wire, 

 which is guided by holes into two cross pieces in the 

 pipe. The ascent of the water into the mouth of the 

 pipe at T pushes in this plug, and closes the pipe. 

 The influx of water now stops ; but the water still 

 flows into B till the elasticity of the air in the lower 

 vessel KE is no longer able to balance a column which 

 reaches to H in the pipe KH. This cessation of the 

 efflux into B generally ceases when KE is half full of 

 water. When this takes place, the workman shuts 

 the cock M, and opens the cock P, from which the 

 water rushes with great velocity. Whenever fths of 

 the water in the vessel TD is discharged at P, which 

 is measured in the vessel which receives it, the work- 

 man opens the cock II with a long rod, so as to fill the 

 vessel KE with water. This drives the air out of KE 

 through the pipe GO into the vessel TD, and conse- 

 quently drives out all the remaining water. Every 

 thing is now in the state in which it was at first, which 

 is known to be the case when no more water flows out 

 at P. The workman, therefore, shuts the cocks P and 

 Q, and opens M, and the same operation is repeated. 

 If the cock N be opened when the efflux has ceased at 

 B, the water and air rush out together with prodigious 

 violence, accompanied with hail and pieces of ice pro- 

 duced by the cold which attends the sudden expansion 

 of air. It is usual to shew this sight to strangers, 

 whose hats, when held opposite N, are sometimes pier- 

 ced with the pieces of ice which are projected from it. 

 A considerable improvement upon this engine has 

 been made by Mr John Whitley Boswell, who has 

 added to it an apparatus which enables it to operate with- 

 out any attending workmen. An account of this im. 

 provement will be found in Nicholson's Journal, 4to. 

 vol. i. and 8vo. No. 5. 



17. Description of the Danaide invented by M. Mannowy 

 Dectot. 



Mannoury This machine consists of a cylindrical trough of tin- 



plate> nearly as hi S h as h is broad > and ha ving a hole in 

 the centre of its bottom. It is fixed to a vertical axis 

 of iron, which passes through the middle of the hole in 

 the bottom, a vacant space being left all round to per. 

 mil the water to escape. The axis turns with the trough 

 upon a pivot, and is fixed above to a collar. 



A drum of tin-plate, close above and below, is fixed 

 upon the axis of the trough, and placed within the 

 trough, so as to be concentric with it, and to leave only 

 between the outer circumference of the drum and the 

 inner circumference of the trough, an annular space 



Dan aide. 



not exceeding 1 }, inches. This annular space communi- Mannowjr 

 cates witli a space less than 1 * inches, left between the 

 bottom of the drum and the bottom of the trough, and 

 divided into compartments by diaphragms fixed upon the 

 bottom of the trough, and proceeding from the circum 

 ference to the central hole in the bottom of the trough. 

 The water comes from a reservoir above by one or 

 two pipes, and makes its way into this annular space 

 between the trough and drum. The bottom of these 

 pipes corresponds with the level of the water in the 

 trough, and they are directed horizontally, and as tan- 

 gents to the mean circumference between that of the 

 trough and of the drum. The velocity which the wa- 

 ter has acquired by its fall along these pipes, makes the 

 machine move round its axis, and this motion accele- 

 rates by degrees, till the velocity of the water in the 

 space between the trough and drum equals that of the 

 water from the reservoir ; so that no sensible shock is 

 perceived of the affluent water upon that which is con 

 tained in the machine. 



This circular motion communicates to the water be 

 tween the trough and drum a centrifugal force, in con- 

 sequence of which it presses against the sides of the 

 trough. This centrifugal force acts equally upon the 

 water contained in the compartments at the bottom of 

 the trough, but it acts less and less as this water ap- 

 proaches the centre. 



The whole water then is animated by two opposite 

 forces, viz. gravity, and the centrifugal force. The first 

 tends to make the water run out at the hole at the bot- 

 tom of the trough; the second, to drive the water from 

 that hole. 



To these two forces are joined a third, viz. friction, 

 which acts here an important and singular part, as it 

 promotes the efficacy of the machine, while in other 

 machines it always diminishes that efficacy. Here, on 

 the contrary, the effect would be nothing were it not 

 for the friction, which acts as a tangent to the sides of 

 the trough and drum. 



By the combination of these three forces, there ought 

 to result a more or less rapid flow from the hole at the 

 bottom of the trough : and the less force the water has 

 as it issues out, the more it will have employed in mo- 

 ving the machine, and of course in producing the use- 

 ful effect for which it is destined. 



The moving power is the weight of the water run 

 ning in, multiplied by the height of thereservoir from 

 which it flows above the bottom of the trough ; and 

 the useful effect is the same product diminished by half 

 the force which the water retains when it issues out of 

 the orifice below. 



In order to ascertain, by direct experiment, the 

 magnitude of this effect, MM. Prony and Carnot fixed 

 a cord to the axis of the machine, which, passing over 

 a pulley, raised a weight by the motion of the machine. 

 By this means, the effect was found to be VET of the 

 power, and often approached ^f^ without reckoning 

 the friction of the pullies, which has nothing to do with 

 the machine. This effect exceeds that of the best 

 overshot wheels. See the Report of the Institute, 23d 

 August 1813; or Thomson's Annals of Philosophy, 

 vol. ii. p. 412. 



For farther information on Hydrodynamics, see AD 

 HESION, BARLEY Mill, CAPILLARY ATTRACTION, PNEU- 

 MATICS, PUMPS, RIVERS, and WATERWORKS. 



HYDROMETER. See HYDRODYNAMICS, p. 437. 



HYDROPHOBIA. See MEDICINE. 



HYDROPHTHALMIA. See SURGERY. 



HYDROSTATICS. See HYDRODYNAMICS, p. 425. 



HYDRUS. See OPHIOLOOY. 



