Introduction

Abstract

As the scope of man’s activities has increased, so has his need for energy. The simple needs of a primitive society, whether of long ago or today, can be met by the use of human or animal energy for mechanical tasks and by the use of wood or dried plant residues or animal excreta as a source of heat energy. And the needs of quite advanced civilisations can be also met with these simple energy sources: our own great cathedrals and castles, the cities of the ancient East and the South and Central Americas were built with human or animal energy alone. But life with these energy sources was slow; a cathedral or a pyramid took years to build and generations passed as some great cities took shape.