504 



HYDRODYNAMICS. 



Conclusions 

 from Ven- 

 turi's expe- 

 riments. 



The preceding Table contains a general abstract of 

 the numerous experiments of Venturi, which were made 

 publicly in the Theatre of Natural Philosophy at Mo- 

 dena. The following are the conclusions which he has 

 deduced from them. 



1. If the part of the additional tube nearest the re- 

 servoir has the form of the contracted vein, the ex- 

 penditure will be the same as if the tube were not con- 

 tracted at all. 



This proposition is deduced from experiments 1, 2, 

 3,4. 



2. The pressure of the atmosphere increases the 

 expence of water through a simple cylindrical tube 

 when compared with that which flows through a sim- 

 ple orifice, whatever be the direction of the tube. 



This proposition is deduced from experiments 5, 6, 

 7, 8, 9, 10. 



3. In descending cylindrical tubes, the upper ends 

 of which have the form of the contracted vein, the quan- 

 tity of water discharged is that which corresponds with 

 the height of the fluid above the inferior extremity of 

 the tube. 



This proposition, which has been established theo- 

 retically in the preceding Chapter, is likewise deducible 

 from experiments 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 

 21,22. 



4. In additional conical tubes, the pressure of the 

 atmosphere increases the expenditure in the proportion 

 of the area of the external section of the tube to the 

 area of the section of the contracted vein, whatever be 

 the position of the tube, provided that its internal fi- 

 gure is adapted throughout to the lateral communica- 

 tion of motion. 



This proposition is established by experiments 23 

 33. These experiments also shew, that, by varying 

 the divergence of the sides of the tube, the lateral com- 

 munication of motion has a maximum and a minimum 

 effect. The minimum is seen in experiment 32. The 

 lateral communication of motion appears to cease to 



produce its effect when the angle of the sides of the 

 tube exceeds 16'. Experiment 23d nearly determines 

 the maximum effect when the same angle is about 30. 



5. The quantity of water discharged is less through 

 cylindrical tubes than through conical tubes which di- 

 verge from the commencement of the contracted vein, 

 and have the same exterior diameter. 



This is established by experiments 35, 36, 37, 38. 



6. By applying proper adjutages to a given cylindric 

 tube, the expenditure of water through that tube may 

 be increased in the ratio of 25 to 10, the head of water 

 remaining the same. 



In order to produce this singular effect, the inner ex- 

 tremity of the tube AD must be filled with a conical 

 piece of the form of the contracted vein, which will in- 

 crease the expenditure from the ratio of 12.1 to 10. 

 At the other extremity of the pipe BC apply a trunca- 

 ted conical tube CD, of which the length must be near, 

 ly nine times the diameter at C, and its external dia- 

 meter D must be 1 .8 C. T x his additional tube will in- 

 crease the expenditure in the ratio of 24 to 12.1, by 

 experiment 27. Hence the expenditure will be in* 

 creased by the two pieces in the ratio of 24 to 20. 



Experiments on the Expenditure of Bent Tubes. 



In order to ascertain the effects of bent tubes, M. 

 Venturi employed two tubes ABC, DEF, 15 inches 

 long, and 14.5 lines in diameter. The portions A, D 

 have the form of the vena contracta, and were applied 

 to the orifice of a reservoir, which was 18 lines in dia- 

 meter, and in which the water was 32.5 inches high. 

 The elbows or flexures BC, EF were made in the plane 

 of the horizon. The tubes were made of copper sol- 

 dered witli silver, and the curvature BC was produced 

 by filling the tube with melted lead, in order that the 

 tube might preserve its diameter during the act of bend- 

 ing. The elbow DEF was rectangular. A rectilineal 

 tube of similar dimensions was also tried, and the fol- 

 lowing were the results. 



PLATE 

 CCCXVIII. 



Fig. 16. 



Venturi's 

 experiment 

 on bent 

 tubes. 

 Fig. IT. 



I 





