= 309 feet, and hence the height of jet is 445 – 309 = 136 feet. The error of 27 feet is considerable, but perhaps not more than might be expected in such an extreme case.

(41.) "Discharge of Jets.”—The quantity of water discharged will vary considerably with the form of the nozzle. The form is also a matter of importance, as affecting the solidity of the issuing stream, and thereby the height of the jet. Fig. 15 shows the best form of nozzle, and Table 9 gives the general proportions TABLE 9.-Of the PROPORTIONS of NOZZLES for JETS.

for different sizes.

The lip at E projecting beyond the mouth

is intended to protect the bore from indentation by accident. The discharge by well-made nozzles of this form will be about 943, the theoretical discharge being 1.0, and may be found direct by the following rule :

In which H = the head of water on the jet in feet. d = the diameter in ths of an inch.

G = gallons discharged per minute.

Table 10 has been calclated by this rule.

(42.) "Jets at the End of Long Mains."-When a jet is placed at the end of a pipe, or series of pipes, as is usually the case,

TABLE 10.-Of the DISCHARGE of JETS with DIFFERENT HEADS.

70

2.01 4.52

8.03 12.5

18.1

24.5 32.1 50.1

72.3

98.4 129

201

289

393 514

650 803

80

2.14 4.83

8.58 13.4

19.3

26.3 34.3 53.6

77.2 105 137

215

309

421 549

695

858

62.9
16.4 23.6 32.6 42.0 65.7
17.1 24.6 33.5 43.7
17.7 25.5 34.8 45.4 71.0 102 139
18.4 26.4 36.0 47.0

300

175 3.17 7.14 12.7 19.8 28.5 39.0
200 3.39 7.63 13.5 21.2 30.5
250 3.79 8.53 15.1 23.7 34.1
4 15 9.35 16.6 25.9

calculation must be made of the loss of head by friction in such pipes, so as to obtain the actual head on the jet, for which alone the rules and Table apply. Say, for illustration, we take the case, shown by Fig. 16, of a jet 1 inch diameter, 70 feet high, at the end of a long main 6 inches, 5 inches, and 4 inches diameter, of the respective lengths given by the Figure, and that we have to calculate the head necessary. Table 8 shows that a et 1 inch diameter, 70 feet high, requires 80 feet head; and Table 10 gives the discharge of the same jet, with 80 feet head, at 137 gallons. Then, by Table 3, we calculate the friction of the mains, and we have the following results :

(43.) In other cases we may have the head and diameter of pipes and nozzle given, and have to determine the discharge. This case is illustrated by Fig. 17, and in dealing with it, we must follow the course indicated in (13). Say we assume the discharge at 300 gallons; Table 10 shows that a jet 11⁄2 inch diameter requires about 75 feet head for that quantity. Then, by Table 3, we find the friction of the mains as follows:—

So that for our assumed discharge of 300 gallons we require only 121 12 feet, instead of 150, the head at disposal. Then by the rule in (13) the true discharge with 150 feet head will be 300 × √150

121.12

=

334 gallons. In such cases as this, where the

height of a jet is involved, the discharge assumed should be pretty near the true one.

(44.) In another case we might require to find the diameter of one of the main pipes, having all the rest given. Thus, say that we have to find the diameter of the pipe P, in Fig. 18. Table 8 gives 90 feet as the head for 11 jet 80 feet high; and Table 10 gives 227 gallons as the discharge of the same jet with 90 feet head.

Then, 11 jet 80 feet high, by Table 8 90.0 feet head
Friction of 6-inch main = .028 × 400 .. 11.2

101.2 "9

We have therefore 115 101.2 = 13.8 feet of head left for

the friction of the pipe P, or

by Table 3 is equal to a 5-inch pipe with say 230 gallons, and this is the required diameter of the pipe P.

(45.) "Path of Fountain Jets."-When the discharge takes place obliquely, or out of the perpendicular, the path of the jet is a parabola, and may be conveniently described by the method shown in Fig. 23, in which we have a jet discharging upward at an angle of 45°, and with a head of 14 feet, which by Table 11 will give a velocity of 30 feet per second, or 3 feet per tenth of a second. If we mark on the line S, E a series of points A, B, C, &c., 3 feet apart, they would show the position of a particle of water at each tenth of a second if gravity did not act: but of course gravity does act simultaneously, and Table 12 gives the space fallen through each tenth of a second, which, being plotted on the perpendiculars drawn through each of the points A, B, C, &c., will give the true position of the particle of water at each tenth of a second. Thus, in ths of a second it would have arrived at C, if uninfluenced by gravity, but the Table shows that in that time a body falls 1 foot 51 inches; therefore F is the true position at that moment, and so of the rest, as in the Figure, which gives the path for two seconds. The lower curve S, T in Fig. 23, shows the path of a jet with the same head and velocity projected downwards at the same angle of 45°. Fig. 19 gives the path for a horizontal projection, and also

TABLE 11.-FALLING BODIES, giving the SPACE fallen through to acquire certain VELOCITIES.

Velocity in Feet

per Second.