Introduction

Physics is a tree with many branches, and fluid dynamics is one of the older and sturdier ones. It began to form in the eighteenth century, when Euler and Daniel Bernoulli set out to apply the principles which Newton had enunciated for systems composed of discrete particles to liquids which are virtually continuous, and it has been in active growth ever since. Nowadays it is partially obscured from view by branches of more recent origin, such as relativity, atomic physics and quantum mechanics, and students of physics pay rather little attention to it. This is a pity, for several reasons. Firstly, because of the engineering applications of the subject, which are many and various: the design of aeroplanes and boats and automobiles, and indeed of any structure intended to move through fluid or propel fluid or simply to withstand the forces exerted by fluid, depends in a critical way upon the principles of the subject. Secondly, because fluid dynamics has important applications in other branches of physics and indeed in other realms of science, including astronomy, meteorology, oceanography, zoology and physiology: dripping taps, solitary waves on canals, vortices in liquid helium, seismic oscillations of the Sun, the Great Red Spot on Jupiter, small organisms that swim, the circulation of the blood – these are just a few of the very varied topics involving fluid dynamics which have been occupying research scientists and mathematicians of international reputation over the past few decades.