Sir Diarmuid Downs, CBE, FEng, FRS Engineering is about designing and making marketable artefacts. The element of design is what principally distinguishes engineering from science. The engineer is a creator. He brings together knowledge and experience from a variety of sources to serve his ends, producing goods of value to the individual and to the community. An important source of information on which the engineer draws is the work of the scientist or the scientifically minded engineer. The pure scientist is concerned with knowledge for its own sake and receives his greatest satisfaction if his experimental observations fit into an aesthetically satisfying theory. The applied scientist or engineer is also concerned with theory, but as a means to an end. He tries to devise a theory which will encompass the known experimental facts, both because an all embracing theory somehow serves as an extra validation of the facts and because the theory provides us with new leads to further fruitful experimental investigation. I have laboured these perhaps rather obvious points because they are well exemplified in this present book. The first internal combustion engines, produced just over one hundred years ago, were very simple, the design being based on very limited experimental information. The current engines are extremely complex and, while the basic design of cylinder, piston, connecting rod and crankshaft has changed but little, the overall performance in respect of specific power, fuel economy, pollution, noise and cost has been absolutely transformed.