As a follow-up to his previous SAE book, The Antiquity of the Internal Combustion Engine 1509-1886, author Horst O. Hardenberg covers the "middle ages" (1794-1886) and that era's developments in "medieval" (that is, compressionless) engines. This book covers reciprocating I-C engines, namely, machinery in which the working process is cyclically repeated; to which the fuel is supplied during each individual cycle; in which the combustion takes place before or in the engine cylinder; and in which the resulting combustion gases represent the working medium. It was not until near the end of the Middle Ages of the I-C engine that gaseous and liquid hydrocarbons proved to be particularly suitable as engine fuels. Thus, this period is characterized by numerous efforts to use a large variety of combustible materials (solid, gaseous, and liquid), and well as explosive substances. All kinds of contraptions were indiscriminately considered, from gunpowder engines to coal-dust-fueled machinery.