510 



HYDRODYNAMICS. 



Motion of town, the engineer has next to consider what diameter 

 Water in of pipe is necessary to convey the quantity of water re- 

 ""* quired. The quantity of water discharged will ob- 

 , viously depend upon the diameter of the conduit pipe, 

 and on the velocity with which the water issues from 

 it. Hence, if we can find the velocity of the water, 

 the diameter will be easily ascertained. 



The experiments of which we have already given a 

 full account, enable us to determine, with very great 

 accuracy, the velocity with which water will issue from 

 an orifice of any form, or from short cylindrical or co- 

 nical tubes, either simple or compound ; and hence we 

 can easily ascertain the velocity with which the water 

 will enter the pipe, or its initial velocity ; but these ex- 

 periments afford us no assistance in ascertaining the va- 

 rious obstructions which the water suffers in its pas- 

 sage so as to determine the velocity with which it issues 

 from a pipe of a gi'e?i length and diameter. 



In order to obtain practical rules relative to this in- 

 teresting subject, many v.-luable and laborious experi- 

 ments have been made. The most celebrated indivi- 

 duals who have devoted their attention to this branch 

 of hydrodynamics, are Bossut, DuBuat, M. Prony, and 

 M. Girard, by whose labours the art of conducting wa- 

 ter has been brought to a very high degree of perfec- 

 tion. It shall therefore be our principal object in the 

 present Chapter to give an account of the experiments 

 of these eminent individuals. 



SECT. I. Account of the Experiments of Bossut and Cott- Motion of 

 plet on the Motion of Water in Conduit Pipes and 

 Open Canals. 



Pipes and 



Canals. 



THE experiments of Bossut were made upon an emi- 

 nence near the springs by which the town of Mezieres 

 is supplied with water. Two reservoirs were excava- 

 ted, one of which furnishes water to the second, in 

 which it stood at a constant height. The first of these 

 reservoirs contained from 25 to 30 cubic toises of wa- 

 ter, and the second was considerably less in magnitude, 

 so as to contain only about six cubic toises of water when 

 it stood at its greatest height, which was about 4 \ feet. 

 A horizontal tube of white iron, about eight or nine 

 inches in diameter, communicated with the bottom of 

 the small reservoir, and terminated in a cubical box of 

 white iron, about one foot broad, and shut up on all 

 sides. To one of the vertical faces of this box, were fit- 

 ted perpendicularly two straight pipes of white iron, 

 one of which had sixteen lines of interior diameter, and 

 the other twenty-four lines. Various lengths of these 

 pipes were employed, between 30 and 180 feet. At 

 different distances, small holes were perforated, in or- 

 der to facilitate the exit of the included air. These 

 apertures were afterwards stopped up by a little wax. 

 In this way, M. Bossut obtained the results contained 

 in the following Table. 



TABLE I. Containing the Quantities of Water discharged by Conduit Pipes of different lengths and diameters, com* 

 partd with the Quantities discharged from additional tubes inserted in the same Reservoir. 



Explanation This Table contains two sets of experiments, one set 

 of tbcTable. on the relative quantities of water discharged by an ad- 

 ditional tube 16 lines in diameter, and a pipe of various 

 lengths of the same diameter ; and another set on the 

 relative Quantities discharged by an additional tube 24 

 lines in diameter, and a pipe of various length and of 

 the same diameter. The fifth and eighth columns con- 

 tain the ratios of these discharges, which are also the 

 ratios of the velocities with which the water issues from 

 the additional tube and the extremities of the pipes. 



Even at the short length of 30 feet, the velocity with 

 which the water issues from the pipe is nearly one half 

 of that with which it issues from the tube, and when 

 the pipe is 180 feet long, and i's diameter 16 lines, the 

 ratio of the velocities is only 100 to 166, so that the 

 water has lost 5-6ths of its initial velocity by its fric- 

 tion on the sides of the pipe. 



It is obvious from a comparison of columns 5 and 8, 

 that the diminution of the velocity is greatest in small 

 pipes ; a result which arises from the frictiou having a 



ments of 

 Butsui. 



