In this fifth edition of a book formerly known as “Hydraulics” the title has been changed to “Fluid Mechanics” in order to emphasize the fact that the treatment is not confined to water or even to liquids but is
applicable to all fluids, including vapors and gases. Also, it is intended to indicate that, so far as possible with our present knowledge, the equations are based upon rational principles and that less dependence is placed upon purely empirical equations. The rational approach results in equations which are more generally applicable and which can be extrapolated with safety beyond the limits of existing data. Empirical equations, which played a large part in the field of hydraulics in early years, might be accurate for special conditions and within limits but cannot be applied in general.