Although not intended primarily as a child’s book, the interest-compelling pictures and clear, illuminating answers to the constant avalanche of questions suggested by the growing mind, unite in making far happier children in the home and brighter children at school. Parents and teachers will also recognize the opportunity to watch for subjects by which the child’s interest appears to be more than ordinarily attracted, and, in so doing, will be enabled to guide the newly-formed tendencies into the proper channels. With the greatest thinkers of the age advocating vocational training, and leading educators everywhere pointing out that the foundation of a practical education for life must be laid in the home, thoughtful parents will not overlook the fact that a book which both entertains and instructs is of supreme importance in the equipment of their children. In the preparation of this book its function has been considered as that of gathering up some of the multitudinous bits of information of interest, both to the inquiring child and the older reader, and putting them in shape to be digested by the ordinary searcher after knowledge. The book is intended, not for a few technical specialists, but for the larger number of men, women and children who are not interested in exhaustive treatises, but who are seeking to gain some fair idea about the numberless every-day subjects that arise in ordinary conversation, or that they meet with in reading and about which they desire some definite and satisfactory information. Most of us realize that we live in a world of wonders and we recognize progress in industries with which we come in personal contact, but the daily routine of our lives is ordinarily so restricted by circumstances that many of us fail to follow works which do not come within our own experience or see beyond the horizon of our own specific paths. The workman who tends the vulcanizer in the rubber factory has come to take his work as a matter of course; the man who assembles a watch, or a camera, is not apt to appreciate the fact that there have been marvelous developments in his line of manufacturing; the operator of a shoe machine, or of an elevator, does not see anything startling or absorbing in the work--and so we find it almost throughout the entire list of industries. The tendency of the seemingly almost imperceptible movement marking onward development in the work that is familiar is to dull the mind toward opportunities for improvement in the accustomed task. With the exception of the man who is at times impressed with the remarkable advances made in some strikingly spectacular industry, because such knowledge comes to him suddenly, the average workman is often too much inclined to regard himself as a machine, and performs his duties more or less automatically, without attempting to exercise imagination or those powers of adaptation upon which all progress has been builded.