564 



HYDRODYNAMICS. 



Hydraulic 



Quadrant, 



&c. 



Hydraulic 

 Quadrant. 

 PLATE 

 CCCXXIII. 



Fig. 4i 



of the bent tube of glass MNO, a simple tube of white 

 iron, sufficiently large to admit a float for pointing out 

 the height of the water in the tube. The lower end of 

 the white iron tube is bent back as at MN, and is ter- 

 minated by a plane surface, perforated at its centre 

 with a small orifice, which will greatly diminish the 

 oscillations of the elevated column. If we then take 

 two thirds of the height of the water in the tube above 

 the level of the stream, we shall have very exactly the 

 height due to the velocity of the current for the depth 

 to which the orifice is immersed. See Pitot, Mem. 

 Acad. Par. 1730, 1772, p. 363; Du Dual's Principes 

 tl'Hydrauliqite, torn. ii. p. 332, edit. 1786; Bossut's 

 Tra'ite d' Hydrodynamiq>ie, torn. ii. p. 267, 268, edit. 

 1796. 



5. Description of the Hydraulic Quadrant for measuring 

 the Velocity of Water. 



The hydraulic quadrant which has been recommend- 

 ed by several authors for measuring the velocity of wa- 

 ter, is shewn in Plate CCCXXIII. Fig. 4% It consists of 

 a quadrant ABC, with a divided arch AB, and having 

 two threads moving round its centre. One of these CP 

 is short, and carries a weight P, which always hangs 

 in air, while the other CH or CM is longer, and carries 

 a weight whose specific gravity is greater than that 

 of water, and which plunges more or less deep in the 

 current as the thread is lengthened. The instrument is 

 then held as in the figure, so that the plummet CP 

 passes through ; and the angle ACD, or the angular 

 distance of the other thread from a vertical line, will be 

 a measure of the force, and consequently of the velocity 

 of the current. Bossut has shewn that the force is as 

 the tangent of the angle ACD, and that if be the ve- 

 locity when the thread has the position CH, and V the 

 velocity when it has the position CM, we shall have 

 .XCR 



fore know , we also know V. We have therefore only 

 to determine u, when H is at the surface, for any 

 given angle ACD, and V will be had for any other 

 velocity, either at the surface or at any depth below it. 

 See Bossut's Traite d'Hi/drody?iamique, torn. ii. p. 265, 

 266. Eytelwein's experiments with the hydraulic qua- 

 drant will be found in the Samml. zur Bauk. 1799. 



6. Machinesfor discharging a uniform Quantity of Water. 



Floating In Plate CCCXXIII. Figs. 5, 6,7, we have represent- 



tube. ed three ingenious contrivances for discharging equal 



Fig. 5. quantities of water from a vessel which is constant- 

 ly emptying itself, or where there is a variable head of 

 water. The contrivance in Fig. 5. where MNOP is a 

 . vessel nearly full of water, consists of a tube BA mo- 

 ving round a joint at B, and having its upper end B 

 connected with a hollow floating ball C. The velocity 

 with which the water enters the extremity B is that 

 which is due to the height BC, or the depth of B be- 

 low the surface. As the surface MN descends the 

 float C also descends, so that whatever be the height 

 of the water in the vessel, it will always enter B with 

 the same velocity. The discharge at the other end A 

 will not be quite uniform, as the water will acquire 

 greater velocity in descending the tube BA when it is 

 much inclined than when it is nearly horizontal. 

 Floating A floating syphon, which produces the same effect 



syphon. in a more correct manner, is shewn in Fig. 6, where 

 ABD is a syphon with a hollow floating ball at its 

 shorter end. This syphon is suspended by the chains 

 iP, EP, which pass over two pulleys P, P upon a ho- 

 rizontal axle PP, and suspend at their other extmni- 





ties counterweights W, W. As the water in the vessel Floating 

 MNOP sinks by being discharged at D, the syphon Syphon. 

 descends and the counterweights, rise, and an uniform *"" ""V" * 

 stream is obtained till the end A reaches the bottom of 

 the vessel. 



Another very ingenious contrivance for the same pur- Floating 

 pose is shewn in Fig. 7- A cone AB attached to a cone - 

 lenticular float C, and fixed upon the axis ef, rises and PLATE 

 falls in the aperture m n, by which the water of the CCCXXIH. 

 vessel MNOP is to be discharged. It is kept in an up- *' 

 right position by the horizontal axes op, rs. Now, when 

 the vessel is full of water, and the head therefore great, 

 the velocity at in n will also be great ; but as the float C 

 rises with the surface MN, the aperture m n will be 

 partly filled by a thicker part of the cone AB ; where- 

 as, when the surface MN has descended, the float AB 

 will also descend, and the aperture at m n will be widen- 

 ed, in consequence of a smaller part of the cone being 

 included in it. In this way, the varying diameter of 

 the cone always adjusts the aperture mn to the varia- 

 ble head of water, so that the quantity discharged 

 through the tube m n o p is nearly always the same. 



7. Water-blowing Machine, or Shower-Bellows. 



The water-blowing machine, called trombe by the 

 French, seems to have been first introduced in Italy 



,. w ,, . * * niat'iiinc 



about the year 1672, for the purpose of procuring a j.-; g g. 

 blast of air by the descent of water. It is repre- 

 sented in Figs. 8 and 9, where MN is a reservoir 

 of water, in the bottom of which is inserted a long 

 tube AB, consisting of a conical part a b, seen upon 

 an enlarged scale in Fig. 9, communicating with a 

 cylindrical tube d B, which enters the vessel CDEF. 

 A number of openings c, d, &c. are made at the top of 

 the tube d B, so that when the water is discharged at 

 the conical aperture b, it drags along with it the adja- 

 cent air. This mixture of air and water falls upon a 

 stone pedestal G, so as to separate the air from the wa- 

 ter. The water descends to the bottom of the vessel, 

 while the air escapes through the pipe C1K to supply 

 the furnace. Another form of the machine is shewn in 

 Fig. 9. where , ft is the conical pipe, and the water Fig. 9. 

 is supplied with air from the pipes x. /3, 3 /3. 



In the water-blowing machines used in Dauphiny, 

 in the neighbourhood of the town of Alvar, the diame- 

 ter of a 6 is 12 inches at a and 5 at b ; the diameter of 

 dB is 10 inches. Only four holes are used at c, d, and 

 the end B enters 1^ feet into the vessel CDEF, which 

 is 4 feet high and 4 feet broad. The water is dischar- 

 ged at an aperture above F, a foot in diameter ; and 

 sometimes the admission of the water and its discharge 

 are regulated by sluices m and n. A strong, equal, and 

 continued blast is obtained by this machine ; but it ia 

 thought to be too moist and too cold. We have seen 

 in Switzerland one of these machines working with 

 great effect at the lead works of M. Lenay, in the val- 

 ley of Servoz near Chamouni. 



Kircher appears to have been the first who explained Venturi's 

 the production of wind by a fall of water. Barthes theory of 

 long afterwards gave another theory, and Dietrich and y^[ n 

 Fabri ascribed the wind to the decomposition of the 

 water. In 1791, the Academy of Thoulouse invited 

 philosophers to investigate this phenomenon, and it 

 was probably in consequence of this that Venturi di- 

 rected his attention to the subject. This ingenious phi- 

 losopher has proved, that the air is dragged down upon 

 the principle of the lateral communication of motion in 

 fluids; and he has pointed out the best mode of construct- 

 ing the machine, so as to produce the greatest quantity 

 of air. The diameter of the tube d B should be at least 



