It has been the steam hammer and the ensuing modifications of it that have made possible the making of large forgings of iron and steel. It has been the large forgings of iron and steel that have made possible the use of large solid masses of those metals in the construction of engines, guns, shells, houses, bridges and ships. It is the ability to use large and solid masses of iron and steel, free from holes and seams, that has enabled constructors and engineers to produce the tremendous engineering structures that characterize today. _The main element in the progress of the race has been its triumph over the forces of material Nature._ This triumph has been gained by inventors, who conceived of certain methods and devices (clothing, for instance) by means of which materials provided by Nature could be utilized by man to protect himself against her attacks upon him--attacks by cold, for instance. Inventions of the useful kind have had a history of their own, as definite as the history of any other thing or things, in which it is shown that every useful instrument or method has been succeeded by another and better; so that the history of useful inventions may be compared to a picture of men mounting a flight of stairs toward civilization, the steps of the stairs being the successive useful inventions of different kinds. The paragraph just written is not intended to mean that inventions which please have no value, but merely to point out the difference between what are aptly called the fine arts and the useful arts. There would be little happiness given to man by toilsomely climbing the stairway to civilization, unless he were occasionally cheered on the way by a strain of music, or a beautiful painting, or a poem, or a brisk walk in northwest weather, or a gladdening glass of wine. It may be argued that these are the things that really give happiness; it may be claimed that these things go direct to the seat of happiness in the brain, but that steam hammers merely provide a material civilization, which continuously promises to make men happier some day, but never makes them happier. Verily, verily, the way to happiness is not so clearly marked, that anyone can walk in it all the time, or even for five minutes, except on rare occasions. The consensus of opinion seems to be, however, that the civilized man is, on the whole, happier than the savage; that civilization is preferable to savagery. It is the purpose of this book, moreover, merely to point out that that structure of civilization has become so complicated and is moving so fast that it is now a veritable machine and to indicate the part that invention has taken in building it.