ERRATA. Page 19, line 25. for Q =m SV 2gH=0.62 SV 2gH=4.96SVH read Q=mSV2gH= 0.62 SV 2gH=4.96 SV H; 23, 4 from bottom, for Q=0.82 SV2gH=6.56 S√H=5.152d2√ H. 29,,, 27, for (Fig. 13) read (Fig. 15). 30, 99 52, " 63, 6, for Fig. 13 read Fig. 15. 9, for 29.128 cubic feet read 35.84 cubic feet. 67, lines 1-4 should be placed after formula at top of page 65. 89, line 25, for great read small; and line 26, for small read great. 97, " H; line II, for n ̧n read nm. 2, for mr = H1 read nr= which binds them together. These bodies are divided into two classes, the incompressible, or fluids properly so called, and the elastic. Water is the more common type of the former, and 3. Although all fluids, as indeed every substance in nature, is in strictness both compressible and elastic, yet the difference in degree is so marked, and the distinction in the expression of their laws so essential under this point of view, that this di- vision must be retained, and hence we have Hydraulics, pro- perly so called, treating of the incompressible fluids, especially water, and Aerometry, treating of the atmosphere and gases. 4. Before entering on the former we must state the values of two quantities which occur in all calculations in Hydraulics, namely, the weight of water, and the measure of the force of B* INTRODUCTION. I. THE science of Hydraulics has for its object the knowledge of the phenomena of fluids in motion, and of the laws which regulate the production of these phenomena. Applied as an art, its object is to render this knowledge available in the designs of the civil engineer, as in the determination of the dimensions of pipes for conveying water, gas, or air, and also in works for the collecting, conveying, and distributing the necessary supply of water, for mill-power, or for the summit levels of canals; or for the supply of cities; and, more generally, of all such works as depend for their suitable construction and proportions upon the result of calculations requiring a knowledge of the pressure and motion of fluids. 2. Fluids are defined to be bodies whose particles, by reason of their extreme mobility, yield to every the least force; they have, however, a certain degree of adherence or viscidity which binds them together. These bodies are divided into two classes, the incompressible, or fluids properly so called, and the elastic. Water is the more common type of the former, and the atmosphere of the latter. 3. Although all fluids, as indeed every substance in nature, is in strictness both compressible and elastic, yet the difference in degree is so marked, and the distinction in the expression of their laws so essential under this point of view, that this division must be retained, and hence we have Hydraulics, properly so called, treating of the incompressible fluids, especially water, and Aerometry, treating of the atmosphere and gases. 4. Before entering on the former we must state the values of two quantities which occur in all calculations in Hydraulics, namely, the weight of water, and the measure of the force of gravity. B* In statements of this nature we should carefully distinguish between those that are mere arbitrary definitions and those which are but inferences from the definition, and also those which are natural quantities, determined by experiments. A cubic foot of water weighs 62.32106 lbs. avoirdupois, the foot being the third part of a brass bar, constructed by Mr. Bird about the year 1760 from the mean of several old and inconsistent standards then existing, and which bar was in 1824 declared by Act of Parliament to be the unit of measures of length, and named the "Imperial Standard Yard." The pound avoirdupois was by the same Act defined to be 7000 grs., the grain being thus determined:-A weight of two pounds Troy having been constructed by the same artist that made the standard yard above mentioned, the half of it (one pound Troy) was divided into 5760 grs. (12 oz. x 20 dwts. x 24 grs.), and 7000 of these grains are equal to one pound avoirdupois. Measures of capacity have for their unit the gallon, which was defined to contain 10 lbs. av. weight of water,—the thermometer at 62° Fahr., and the barometer standing at 30 inches. A cubic inch of water, at the same temperature and pressure, was found by experiment to weigh in air 252.458 grs.; and hence, if we divide 70000 by 252.458, we shall have the number of cubic inches in the imperial gallon, which, therefore, is equal to 277.274 cubic inches; and if we multiply 252.458 by 1728, the number of cubic inches in one cubic foot, we have, as above, 62.32106 lbs.: hence, also, 6.23 imperial gallons to one cubic foot. The cubic foot of water is, in practice, supposed to be equal to 62.5 lbs. av., or 1000 ozs. at 16 ozs. to the lb.; and we also have 36 cubic feet to a ton, or 6 tons to a cubic fathom. The measure of the force of gravity is the velocity acquired in one second by a body falling freely from a state of rest, and is equal to 32.1948 feet per second, and always denoted by the letter g. 5. The Mètre adopted in France in 1798 as the unit of lineal measures is equal to 39.37079 inches. It is therefore 3.28089 feet, and is subdivided decimally into the decimetre, the centimetre, and the millimètre; and in order to assist the forming a clear idea of the comparative value of the French and English lineal measures, they have been drawn on Plate I. from a common zero. The cubic decimetre of water at 39.38°F., and barometer at 29.922 inches, is the standard of weight named the Kilogramme, 2.20485 lbs. av. - Vide Galbraith and Haughton's Arithmetic, 2nd edition, Tables of Foreign Weights and Measures. = |
