422 



HYDRODYNAMICS. 



History, the ordinary theory of resistance, with the experiments 

 v *^"y"'^ by which it has been corrected anil rendered applica- 

 ble to practice. M. Prony then proceeds to give an ac- 

 count of the general and rigorous theory of the motion 

 of fluids, and he applies the equations to the motion of 

 fluids in narrow pipes. In the 5th section, which con- 

 tains much valuable practical information, the author 

 has treated at great length the subjects of friction and 

 of the strength of men, and has given a detailed ac- 

 count of the history and construction of the steam en- 

 gine, from the rude form in which it came from the 

 hands of the Marquis of Worcester to the almost per- 

 fect state to which it has been brought by our celebra- 

 ted countryman Mr Watt. 



F ri- In the year 1795, Mr Vince of Cambridge publish- 



ments of ed in the Philosophical Transactions his Observations 

 Mr Vince, on the Theory of Ike motion and resistance of Fluids, 

 A.D. 1795 M ji/ t a Description of the Construction of Experi- 

 .iiul 1798. me ,,t$ in order lo,oblain some fundamental principle ; and 

 in the year 1798, he published, in the Transactions of 

 that year, another paper, entitled, Experiments on the 

 Resistance of Bodies moving in Fluids. The experi- 

 ments contained in the first of these papers, were made 

 chiefly with the view of ascertaining how far the theory 

 of the motion of fluids could be applied to the discharge 

 of water from vessels. Mr Vince has concluded, from 

 the results of this inquiry, that the great difference 

 between the experimental and theoretical results, in 

 most of the cases which respect the times in which 

 vessels empty themselves through pipes, leads us to 

 euspect the truth of the theory of the action of fluids 

 under all other circumstances. In the second memoir, 

 he gives an account of a variety of experiments on the 

 resistance of fluids, when the resisted body is immersed 

 at some depth in the fluid made with a particular ap- 

 paratus which he contrived for this purpose. The re- 

 sults which he obtained differ widely from those ob- 

 tained by Bossut with bodies floating on the fluid, 

 which Mr Vince explains, by supposing, that at the 

 surface, the fluid from the end of the body may escape 

 more easily than when the body is immersed below the 

 surface. 



The late Dr Matthew Young, Bishop of Clonfert, 

 made a number of experiments on the efflux of fluids 

 from orifices of different kinds, of which he has pub- 

 lished an account in the 7th volume of the Transaction* 

 of the Royal Irish Academy. In order to explain the 

 increase in the discharge by inserting an additional 

 tube in an orifice in the bottom of a vessel, he filled a 

 cylindrical vessel with mercury to the height of 6 in- 

 ches, and inserted in its bottom a tube 7.8 inches long. 

 Having closed the orifice of the pipe, he placed the ap- 

 paratus under the receiver of an air pump, when the 

 barometer was at 30 inches, and the gauge at 28|, 

 the time of the efflux was in this case 26 seconds ; 

 but when the experiment was repeated in the open air, 

 without any variation, the time of the efflux was only 19 

 seconds. Unless the gauge stood higher than 22^ inches, 

 no difference was observed in the times of the efflux in 

 the open air and in the receiver. When the efflux was 

 made in vacua, the pipe was not filled during the efflux, 

 as it was when the discharge was made in the open air. 

 Hence Dr Young concludes, that the plate of fluid at 

 the orifice, where the additional tube is inserted, has 

 its perpendicular pressure increased by the weight of 

 the column of fluid in the additional pipe, without any 

 increase of its lateral pressure ; and, consequently, the 

 quantity of water discharged by a pipe of this kind 



EipsrU 

 Clients of 

 Or Mat. 

 thew 

 Young. 



must exceed that which is discharged by a simple ori- History. 



fice. The results of experiments, therefore, made with "* "V 1 "^ 



additional tubes, will be more consonant to theory 



than when they are made with a simple orifice, unless 



when the tube has such a length that a sensible effect 



is produced by the friction of the fluid against the sides 



of the tube, or when the additional tube is so short as 



not to be capable of giving a vertical direction to the 



particles of water. Dr M. Young found, that tin's 



view of the subject agreed remarkably well with the 



experiments of Mr Vince. 



In the year 1801, M. Eytelwein, of Berlin, who R CS farch 

 was known to the public as the translator of Du of M. Ky- 

 Buat's works into German, and who was honoured telwcin. 

 with several employments and titles relative to the 

 public architecture of the Prussian dominions, publish- 

 ed a work entitled, Handbitch der Mcchanik and der 

 Hydraulik, which contains not merely an exposition of the 

 labours of precedingwriters, but an account of many new 

 and valuable experiments made by the author himself. 

 The second part of this work, which treats of hydrau- 

 lics, is divided into 24 chapters. Chap. 1. Treats of 

 the efflux of water from reservoirs, and of the contrac- 

 tion of the fluid vein. Chap. 2. Of the discharge of wa- 

 ter from horizontal and lateral orifices in a vessel con- 

 stantly full. Chap. 3. Of the discharge of rectangular 

 orifices in the side of a reservoir extending to the sur- 

 face. Chap. 4. Of the discharge from reservoirs with 

 lateral orifices of considerable magnitude, the head of 

 water being constant. Chap. 5. Treats of the efflux 

 from reservoirs which receive no supply of water. 

 Chap. 6. Of the discharge from compound or divided 

 reservoirs. Chap. 7- Of the motion of water in rivers. 

 In this chapter, M. Eytelwein has shewn that the mean 

 velocity of water in a second in a canal, or river, flow- 

 ing in an equable channel, is 4?ths of a mean propor- 

 tional between the fall in two English miles, and the 

 hydraulic mean depth ; and that the superficial veloci- 

 ty of a river is nearly a mean proportional between 

 the hydraulic mean depth and the fall in two English 

 miles. Chap. 8. Treats of the discharge and the swell in 

 the case of falls, weres, and contractions in rivers and 

 canals. In Chap. 9. On the motion of water in pipes, 

 our author expresses the velocity in English feet by the 



following simple formula: wr=5 



- ., where / is 



- ., 



the length of the pipe, d the hydraulic mean depth, 

 and h the height of the reservoir. If the pipe is 

 bent into angles or sinuosities, the value of u must be 

 corrected by taking the product of its square mul- 

 tiplied by the sum of the sines of the several angles 

 of inflection, and then by 0038. This will give the 

 degree of pressure employed in overcoming the re- 

 sistance occasioned by the angles, and by subtract- 

 ing this height from that which is due to the velo- 

 city, we may thence find the corrected velocity. Chap. 

 10. Treats of jets of water. Chap. 1 1. Of the impulse 

 or hydraulic pressure of water. Chap. 12. Of overshot 

 water-wheels. Chap. 13. Of undershot water-wheels. 

 Chap. H. Of the properties of air, in so far as they are 

 connected with hydraulic machines. Chap. 15. Of sy- 

 phons. Chap. 16. Of sucking pumps. Chap. 17. Of 

 forcing pumps. Chap. 18. Of mixed pumps, or the 

 combination of sucking or forcing pumps. Chap. 19- 

 Of acting columns of water. Chap. 20 Of the spiral 

 pump. Chap. 21 . Of the screw of Archimedes. Chap. 

 22. Of bucket wheels or throwing wheels. Chap. 23. 

 Of cellular pumps and Paternoster works. Chap. 24-. 



