*The following is the preface to an old textbook being used as a decoration along with a bunch of other textbooks on a shelf in one of the study rooms of the science building (where I am now even though I don't have any classes in this building, as I am a total loser). What I would like to do is get the preface to a newer book on the same subject for comparisons, but I can already see some things I know would never appear in newer books. I want to note that the author's names are not actually rendered in all caps. They're actually in one of those old fonts where the lower-case letters are sized down versions of capital letters. They used to do that. I don't think very many people do that anymore...*

If one casually glances around, most things seem to be solids, but when one thinks of the oceans, the atmosphere, and on into outer space it becomes rather obvious that a good portion of the earth's surface and of the entire universe is in the fluid state.

Aside from the scientist's interest in the nature of the universe which is mostly gas, the engineer's interest in devices useful to mankind can seldom drift far from fluids. It is indeed difficult to think of any machine, device, or tool which doesn't have some fluid hidden in it somewhere and some fluid mechanics behind its design. Pumps, fans, blowers, jet engines, rockets, gas turbines are primarily fluid machines. Aircraft and ships move through fluids. The atmosphere and the weather are governed by the dynamics of fluids. All machines must be lubricated and the lubricant is a fluid. Even the vacuum tube in a radio relies on an electron gas for its operation. And, no matter how complex or esoteric the device, the basic concepts of fluid dynamics still apply. After one masters the few basic ideas of fluid mechanics, a whole world of applications is opened.

It would seem unnecessary then to justify the obviously important place of fluid dynamics in modern science and engineering. It forms one of the foundations of aeronautics and astronautics, mechanical engineering, meteorology, marine engineering, civil engineering, bio-engineering and, in fact, just about every scientific or engineering field.

This book may be used either as a text or supplementary text for a first undergraduate course in fluid mechanics. However, one of the unique features is the treatment of a a broad spectrum of fluid mechanics topics such as hypersonic flow, magnetohydronamics and non-Newtonian fluids not heretofore found in a single book of this type. The coverage of this material and other advanced topics also make this book ideal for use as a reference and supplementary text for either an intermediate or first year graduate course.

The first few chapters are written primarily for the beginning student, with considerable emphasis on basic ideas of fluid motion. The first three chapters contain rather complete derivations of the conservation equations both in integral and differential form. Many examples are presented in order to convey the very important ideas of a control volume, Bernoulli's equation and the motion of fluids in general. A convenient summary of important equations and a general discussion of problem solving technique, which will be helpful to the beginning student, is provided in Chapter 3.

The level of the book changes from chapter to chapter. Chapters 1 through 5 and Chapter 7 serve as a first introduction to fluid mechanics at the undergraduate level. Chapters 6 and 8 extend to the aerodynamics of subsonic and supersonic flow and are pitched at the advanced undergraduate level.

As the student proceeds through the remaining chapters, he will find that the material becomes more advanced. The second half of the book deals with topics which are of current research interest. For example, the fluid mechanics literature and research efforts of today are largely in areas of incompressible turbulence, hypersonic flow, magnetohydrodynamics, and non-Newtonian fluids. These chapters are written in such a way that one who is not familiar with these particular subfields may obtain an introduction to the form of the mathematical models, the simplifications and techniques, the nature and peculiarities, and the present state of the art. If one is interested in an in-depth study of one or more of the subfields, the references at the end of the chapters may be pursued. These, along with this book, could serve as the based for an individual study program.

The authors wish to thank Dr. E. W. Gaylord for his valuable help with Chapter 12, and Mrs. Dorothy C. Wakefield and Mrs. Mary Bathurst for typing the original manuscript.

J.A. BRIGHTON

W.F. HUGHES

University Park, Pennsylvania

Pittsburgh, Pennsylvania

July, 1967