PREFACE 



WERE water a perfectly non-viscous, inelastic fluid, whose particles, 

 when in motion, always followed sensibly parallel paths, Hydraulics 

 would be one of the most exact of the sciences. 



But water satisfies none of these conditions, and the result is that in 

 the majority of cases brought before the engineer, motions and forces of 

 such complexity are introduced as baffle all attempts at a rigorous 

 solution. 



This being so, the best that can be done is to discuss each phenomenon 

 on the assumption that the fluid in motion is perfect, and to modify the 

 results so obtained until they fit the results of experiment, by the intro- 

 duction of some empirical constant which shall involve the effect of every 

 disregarded factor. 



It is worth while here impressing on the student of the science that, 

 apart from these experimentally-deduced constants, his theoretical results 

 are, at the best, only approximations to the truth, and may, if care be not 

 taken in their interpretation, be actually misleading. 



On the other hand, it may be well to answer the criticism of those who 

 would cavil at such theoretical treatment, by pointing out that the results 

 so obtained provide the only rational framework on which to erect the 

 more complete structure of hydraulics. 



In the following pages an attempt has been made to consider the 

 science, and its application to the design of Hydraulic Machinery, in a 

 manner suitable for a student who has some initial knowledge of 

 mechanics. 



While written primarily with the needs of a student in view, it is, 

 however, hoped that the book may prove of value to such as are actively 

 engaged in the practice and profession of Hydraulic Engineering. 

 Although it has not been attempted to elude the largely imaginary 

 difficulties of a mathematical treatment involving some knowledge of the 

 Differential and Integral Calculus, the knowledge of this subject which 

 is necessary for a thorough grasp of the greater part of the book is very 

 slight. 



Where, as in some few paragraphs, a somewhat more extended 



