The suitability Of oil engines for the purpose has awakened a widespread interest in them. The Editor therefore hopes that this little volume will be especially welcome to non-technical readers who like to keep ahead Of the times in matters Of such universal importance. One chapter deals exclusively with the theory of the gas engine, but the non-technical mind Should have no fear, for mathematics have been as far as possible avoided. It may also serve to dispel wrongful notions concerning the practical limits of the efficiency of gas engines which.