THIS work is intended to furnish engineers, draughtsmen, and students with practical data, based as far as possible on the results obtained after years of experience, by the leading makers of the gas engines which work on the common and well-known four-stroke cycle of Beau de Rochas and Otto.

Whether as an additional help in the study of the subject, from the mechanical standpoint, or as an aid to design in the drawing office, where it may find a welcome place as a companion, it is hoped the book will be found of use, and supply a much-felt want.

With this end in view, the author has spared no pains in seeking the most reliable and up-to-date information. Only actual modern gas engines are considered. The various parts of the mechanism of gas engines, self-starters, and other accessories are illustrated and described in detail. The general arrangement, working, and testing of gas engines are dealt with; and the observations, calculations, and results of some careful and elaborate tests are recorded.

I beg to acknowledge my indebtedness to the various