This. Book deals with principles. There are many books which give a descriptive account of existing types of engines, but my object in writing this volume has been to assist the reader to obtain thoroughly sound notions of the principles of design and construction which underlie all current prac tice. If a man understands, for example, the construction of the elements of a carburettor and how they ought to perform their several functions, he should have no difficulty in understanding any special type of carburettor placed upon the market. In dealing with the subject of ignition I have purposely avoided any detailed explanation of the manner in which the spark discharge is produced, because I felt that it introduces new ideas and probably causes the reader to lose sight of the fact that the magneto is only, after all, an accessory, although of course a most important one. I hope that the accounts of my experiments with the two stroke will be of some service to inventors and others the many extraordinary breakdowns, defects and adventures encountered during this period of my career have not been inserted because they would undoubtedly cause the reader to forget, for the time being, his fundamental principles.