All About Engines

vi Preface application of steam to the propulsion of railway trains and ships. Finally, power and its measure- ments are explained in an elementary way, and the book closes with a chapter on the problems of fuel, upon which the future of mechanical power largely depends. The author has written throughout as for his own boys, and two of them, aged seventeen and thirteen, have read the whole of the proofs without apparently being bored. It is not pretended that they under- stood everything in it; a book of over 300 pages on engines which is wholly intelligible to a boy of thirteen should be burnt rather than printed. At the same time an effort has been made to exclude any discussion of matters which are of greater difficulty than importance. In the selection of material there must always be room for difference of opinion, and in this respect the author craves the indulgence of his readers. In a book of this kind there is ample oppor- tunity for the exercise of judgment, but the essentials are a properly balanced view, numerous illustrations and the avoidance of statements which have to be unlearned by those who at a later stage will acquire their knowledge professionally. Of the 182 illustrations about 150 have been specially drawn for the book, while the rest are re- produced by permission of leading engineers and manufacturers. For help in this and other ways