VELOCITY OF WATER IN PIPES. 205 VELOCITY IN INCHES PER SECOND OF WATER FLOWING THROUGH PIPES WITH VARIOUS SLOPES AND DIAMETERS.—(Continued.) 10 301. 320. 338 20 199. 211. 30 155 165. 223. 372. 403⚫ 432. 459. 484⚫ 597⚫ 692⚫ 245. 256. 285. 303. 320⚫ 394. 456. 192. 208⚫ 223. 238. 250⚫ 309. 358⚫ 40 130. 138 161. 174. 187. 199. 210. 259. 300⚫ 336. 50 113 121 127 140 152 163 173 183 226 261 293 775. 511. 400. 99.5 115. 129. 60 102. 109. 115. 127. 137. 147. 156. 165. 204⚫ 236. 264. 70 93-2 99.0 104. 115. 124. 134. 142. 150. 185. 214. 240⚫ 80 86.3 91.6 97. 106. 115. 123. 131. 139. 171. 198. 222. 90 80.5 85.5 90.4 99.4 107. 115. 122. 129. 159. 185. 207. 100 755 802 85'0 93.5 102 108 115 121 150 173 194 200 50-2 53.3 56-4 62.0 67-2 72.1 76.7 80.8 300 39-9 42.5 45.0 49.5 53.6 57.5 61.1 64.4 79.5 92.0 105. 400 33.8 35.9 38.0 41.8 45.2 48.5 51.5 54.4 67.0 77.7 87.0 500 29'8 31'6 33'4 36'8 39'8 42'8 45'5 479 59'0 68'4 767 600 26.8 28.6. 30-2 33.2 36.0 38.6 41.0 43.2 53.3 61.7 69.2 700 24.6 26.2 27.7 30.4 33.0 35.3 37.6 39.6 48.8 56.5 63.4 800 22-9 24.3 25.7 28.3 30.6 32.9 84.9 36.S 45.4 52.5 58.9 900 21.4 22.7 24.0 26.4 28.7 30.7 32.7 34.4 42.5 49.1 55.1 1000 20.2 21.5 227 25.0 27.1 291 309 32.5 40.1 46'4 520 2000 18.7 14.5 15.4 16.9 18.3 19.7 20.9 22.0 27.2 31.3 35.3 18.5 21.4 24.0 3000 10.9 11.6 12.3 13.5 14.6 15.7 16.7 17.6 21.7 25.2 28.2 4000 9.32 9.90 10.4 11.5 12.4 13.4 14.2 15.0 5000 8.23 8.73 9'25 103 110 11'8 125 13.2 16.3 18.9 21.2 10.0 10.7 11.4 12.0 14.8 9.10 9.76 10.3 10.9 13.5 8.43 9.05 9.62 10.1 12.5 14.5 16.2 7.92 8.50 9-02 9.52 11.7 13.05 15.2 17.1 19.2 15.6 17.5 6000 7.47 7.93 8:40 9.23 7000 6.80 7.22 7.65 8:40 8000 6.30 6.69 7.07 7.78 9000 5.91 6.28 6.64 7:30 10000 5 55 5'91 6'25 6'87 7:45 7.98 8:50 8'93 110 127 14:3 16 feet we must add the fall which would generate the velocity of 29.8 inches per second, namely, 1·15 inches, which will make the total fall 16 feet 1.15 inches that will be requisite to give such a velocity; but in such cases as this it is evident that the addition of this small fraction might have been disregarded. In some cases Messrs. Boulton and Watt have employed the constant 1.82 instead of 2.25. Mr. Mylne's constant is 1.94; but some careful experiments made by him at the West Middlesex Waterworks, gave a constant as high as 2.62. OTHER TOPICS OF THE THEORY OF STEAM-ENGINES. It will not be necessary to extend these remarks by an investigation of the theory of the crank as an instrument for converting rectilinear into rotatory motion, since the idea, once widely prevalent, that there was a loss of power consequent upon its use, is now universally exploded. Neither will it be necessary to enter into any explanation of the structure of the numerous rotatory engines which have at different times been projected, since none of those engines are in common or beneficial operation. The proper dimensions of the cold water and feed pumps, the action of the fly-wheel in redressing irregularities of the motion of the engine, and other material points which might properly fall to be discussed under the head of the Theory of the Steam-Engine, and which have not already been treated of, will, for the sake of greater conciseness, be disposed of in the chapter on the Proportions of Steam-Engines, when these various topics must necessarily be considered. Nor is it deemed advisable here to recapitulate the rules for proportioning the various kinds of parallel motion, since parallel motions have now almost gone out of use, and since also any particular case of a parallel motion which has to be considered, can easily be resolved geometrically by drawing the parts on a convenient scale,the principle of all parallel motions being that the versed sine of an arc, pointing in one direction, shall be compensated by an equal versed sine of an arc pointing in the opposite direction; and the effect of these opposite motions is to produce a straight line. In the case of the parallel motions sometimes employed in sidelever engines, and in which the attachment is made not to the cross-head but to the side-rod, it is only necessary to provide that the end of the bar connected to the side-rod shall move, not in a straight line, but in an arc, the versed sine of which is equal to the versed sine of the arc described by the point of at MODE OF DRAWING THE PARALLEL MOTION. 207 tachment on the side-rod. As the bottom of the side-rod is attached to the beam and the top to the cross-head, and as the bottom moves in an arc and the top in a straight line, it is clear that every intermediate point of the side-rod must describe an arc which will more and more approach to a straight line, or have a smaller and smaller versed sine, the nearer such point is to the top of the rod. By drawing down the side-rod at the end of the stroke, and also, at half stroke, the amount of deviation from the vertical at those positions, can easily be determined for any point in the length of the rod; and the point of attachment of the parallel bar has only to be such, and the length and travel of the radius crank has also to be such, that the end of the parallel bar attached to the side-rod shall describe an arc whose versed sine is equal to the deviation from the perpendicular, or, in other words, to the side-travel of that point of the side-rod at which the attachment is made. Since, then, the side-rod is guided at the bottom by the arc of the beam, and near the top by that less arc described by the end of the parallel bar, which answers to the supposition of the cross-head moving in a vertical line, the result is that the cross-head will be constrained to move in this vertical line; since only on that supposition can the two arcs already fixed be described. The method of balancing the momentum of the moving parts of marine engines which I introduced in 1852 has now been very generally adopted; and the practice is found to be very useful in reducing the tremor and uneasy movements to which engines working at a high rate of speed are otherwise subject. Nearly all the engines now employed for driving the screw propeller are direct-acting engines, which necessarily work at a high rate of speed to give the requisite velocity of rotation to the screw shaft. The principle on which the balancing is effected is that of applying a weight to the crank or shaft, and when the piston and its connexions move in one direction the weight moves in the opposite with an equal momentum. CHAPTER IV. PROPORTIONS OF STEAM-ENGINES. WE now come to the question how we are to determine the proportions of steam-engines of every class. The nominal power of a low pressure engine is determined by the diameter of the cylinder and length of the stroke, as follows: TO DETERMINE THE NOMINAL POWER OF A LOW PRESSURE ENGINE OF WATT'S CONSTRUCTION. RULE.-Multiply the square of the diameter of the cylinder in inches by the cube root of the stroke in feet, and divide the product by 47. The quotient is the nominal horse-power of the engine. Example 1.-What is the nominal power of a low pressure engine with a cylinder 64 inches diameter and 8-feet stroke? Here 64 × 64 = 4,096, which multiplied by 2, the cube root of 88,192 and ÷ 47 = 174.3. The nominal powers of engines of different sizes, both high pressure and low pressure, are given in the following tables: Diameter of Cylinder in inches. TABLES OF NOMINAL POWERS OF ENGINE. 209 NOMINAL HORSE POWER OF HIGH PRESSURE ENGINES. LENGTH OF STROKE IN FEET. 3.30 3.48 3.66 3.93 4.17 4:41 4.59 4.77 8.90 4.08 4-23 4-62 4.89 5.16 5:46 5.61 6.51 8 4.08 4.62 $8 101 7.05 8.04 8.88 11 2-28 2.61 2.88 3.12 2-69 3.09 3.39 3.66 3.12 3.57 3.93 4.23 4.50 4.74 4.95 5.34 5.67 5.97 6.27 3.60 4.11 4.53 4.86 5-19 5.46 4.68 5.16 5.55 5.88 6.21 5-28 5.82 6.27 6-63 6.99 7.32 7-89 6.51 7.02 7.47 7.86 8.22 7.80 8.37 8.76 9-15 9-84 10-47 11-01 11:52 11.98 8.67 9.21 9-69 10-14 10-92 11.61 12.21 12.78 13.29 9.54 10-14 10.68 11-16 12:03 12-78 13:47 14:07 14.64 7.74 8.85 9.72 10:47 11:31 11-73 12:45 13-20 14:04 14-76 15:45 16:05 114 8.43 9-66 10.62 11:46 12-15 12.78 13.80 14.61 15:33 16:14 16.88 17.56) 12 9.18 10:53 11:58 12:48 13-26 13.95 14.58 15-72 16-71 17.58 18:39 19:11 124 9-96 11:40 12:57 13:53 14:37 15:15 15.84 17-04 18-12 19:08 19.92 20.78i 13 10.80 12:36 13:59 14-64 15:57 16:38 16-92 18:45 19:59 20.64 21.57 22:44 134 11.64 13:32 14.64 15.78 16.77 17.67 18-48 19.89 21.15 22-26 23 25 24 19 14 12.51 14:31 15.75 16.98 18-03 18.99 19-86 21-39 22.74 23-94 25-02 26-01 13:41 15.56 16.92 18-21 19:35 20:37 21:30 22.95 24-39 25.62 26.83 27.90 14-31 16:44 18:09 19.50 20-70 21.81 22-80 24.57 26-10 27-48 28-71 29.88 16 16-35 18-69 20-58 22:17 23.58 24.81 25.95 27.93 29.70 31.26 32.67 83.99 17 18.45 21-12 23.25 25.05 26-58 28.02 29.28 31.56 33.57 35-28 36.90 38:37 18 20-67 23.67 26-04 28-08 29-82 31.41 32.82 35-37 37-59 39-57 41.37 43:02 19 23.04 26-37 29-04 31-26 33.51 34.98 36-57 39-39 41.88 44.07 46.08 47.94 20 25-53 29-22 32.16 34-65 36.81 38-76 40-53 43-65 46.38 48.84 51.06 53.10 22 30-90 35-37 38-91 41-94 44.55 46-89 49-86 52.95 56-13 59 10 61-80 64-26 24 36.78 42.09 46-32 49.89 53.01 55.83 58.35 62.85 66.81 70-32 73-53 76.47 26 43.17 49.38 54.36 58.56 62.25 65.52 67 68 73.80 78 42 82.53 86.34 89.76 28 50-04 57-27 63.06 67.92 72-18 75-99 79-44 85.56 90-93 95.70 100-1 104-0 30 57-45 65-76 72-39 77-97 82-86 87-21 91.20 98-22 104-4 109.9 114.9 119 5 82 65.37 74-88 82-53 88.71 94-26 99-24 103-7 111-8 118.7 1250 130-7 136.0 84 73-80 84-48 92-97 100-2 106-3 112-0 117-1 126-2 134-0 141-1 147.6 153.5 86 82-71 94.68 104.2 112.2 119-3 125-6 131-3 1414 1503 158.2 165-4 172-1 38 92-16 105.5 116-1 1250 134.0 136-9 146-3 157.6 1675 176-3 1843 191.7 40 102-1 116-9 129-6 138.6 147.3 1551 162-1 174-6 185-6 195-3 204-2 212 4 42 112-6 128.9 141-8 152-8 162-4 170-9 178-7 192-5 2046 215-3 225-2 234.2 44 123-5 141.4 155.7 1677 178-1 187-6 199-4 2113 224-5 236-3 2471 257.0 46 135.0 154-6 170-1 183.3 194-6 204-6 214-3 2300 245 4 258 3 270-1 280-9 147.0 168.3 185-3 199.6 212-1 223 2 233-4 251.5 267.2 281-3 294.1 306.0 159-6 182.6 201-0 216-5 230-1 242-3 253-3 272.9 289-9 3051 319-2 831-8 52 172-6 197-6 217-4 234-2 249-0 262-0 270-7 295-2 313.5 3300 345 3 358.8 54 1861 213-0 234.5 252.6 268.4 282-6 295-4 318-3 338.1 356.1 372.3 387-0 56 200-1 229-1 252-2 271-6 288-7 303-9 317-7 342-3 363-6 382.8 400-2 416-4 58 214-7 245-8 270-5 291-4 309-6 325-8 340-8 367.2 389-7 410-1 429-3 446-1 60 229-8 263-0 289-5 311-7 331-2 348.9 364.8 393-0 417-6 439-5 459-6 477.9 70 312-8 357-9 393-9 424-5 451-2 474-9 496-5 584 6 568 2 598.2 625.5 650-4 48 50 |