his bit" towards the development of engineering science, be able to devote his remaining working years principally to serving the public in an advisory capacity on important engineering projects—provided that, before the time arrives for him to pass on, the profession shall have extricated itself from the disastrous slump into which it was plunged in 1914 by the advent of the World War.

The reader must not deduce from the preceding that the author desires to convey the impression that his labors in the field of engineering economics are over—far from it!—for he has good reason to expect that he shall be retained some day to investigate the great economic problem of "Molybdenum Steel for Bridges" in the same manner in which years ago he investigated that of "Nickel Steel for Bridges."

The economic studies of the last four years, upon which this treatise is mainly based, have been intensely interesting; but the work involved, which (somewhat unlike that of the writing of the author's magnum opus) has been chiefly personal, and, in spite of steady application and long working hours, exceedingly long-drawn-out, has become rather overpowering; so that, it must be confessed, the ultimate completion of the undertaking, which will not occur until the book is actually issued, will be decidedly in the nature of a relief.

In another particular the preparation of this treatise has differed from that of its predecessor, which (as a side issue, it is true,) necessitated a thorough search of engineering literature; because in this case no searching has been done, the reason being that the subject is almost entirely a new one, and, consequently, essentially independent of past records.

The author hopes that this book will prove of real service to several generations of engineers, notwithstanding the fact that, on account of changes in practice due to the rapid development of the profession, nearly all engineering books are short-lived. Such a hope is not entirely without foundation, because his little "De Pontibus," published nearly a quarter of a century ago, in spite of its contents having been absorbed by its successor, "Bridge Engineering," had a steady sale until about the end of 1920, when the publishers let it go out of print because of its low price combined with the exceedingly high cost of paper, press-work, and binding.

In conclusion, there is a suggestion which the author would like to make concerning a possible utility for this work in combination with its immediate predecessor; but he has long debated as to the advisability of offering it, fearing that some of his readers may either misconstrue his motive or charge him with undue conceit concerning the value of his technical productions. However, he has decided to run the risk; because he greatly desires that the results of the long and arduous labor which he has put upon their preparation shall be utilized to the utmost for the benefit of all future young engineers who have the ambition to specialize in bridgework. The suggestion is this: