In proof of the previous statement that the treatment throughout "Bridge Engineering" is based on the conception of economics, there is offered the following extract from a review of that work written by Albert Reichmann, Mem. Am. Soc. C.E., and published in the October, 1916, issue of the Journal of the Western Society of Engineers.

"In a larger sense, this work is a treatise on the subject of 'Economics of Bridge Engineering.' This train of thought can be traced throughout the entire work, all subjects being treated fully and in a broad way, and with the idea of value constantly brought out."

There is a salient feature of the present book to which attention should be called, and that is the scarcity of treatment of economic problems by pure mathematics, nearly all the formulae given being semi-rational, semi-empirical. The reason for this is that the conditions affecting most of the economic questions in bridge designing are far too complicated to lend themselves to solution by mathematical manipulations. This fact has not always been recognized by engineering writers; for, during the last three or four decades, numerous attempts have been made to settle important economic bridge-problems mathematically, with the result that the conclusions thus drawn have proved to be erroneous and generally totally useless.

It is prognosticated that, in the future, there will be no such fundamental changes in methods of bridge design and construction as to render really incorrect the numerous economic conclusions reached herein; because bridge building has now become fairly well systematized. About the only important change in sight is the adoption of high-alloy steel for long-span superstructures; and the effects of this have been duly anticipated. The reasons for this belief are that the investigations upon which the book is based were in general predicated upon fundamental engineering principles that do not vary; and that the effects of possible changes in unit prices of materials in place and in other general conditions affecting design have been indicated. While it is true that an abnormal variation of a temporary nature in the unit price of some important material of bridge construction, some peculiar feature of structure-location affecting erection, or possibly some other cause, may change somewhat the findings stated herein, it must be remembered that, as pointed out in several places, up to a certain limit a considerable divergence from the exact economic condition will usually cause no serious augmentation of total cost. This is the saving clause which renders the author's economic conclusions sufficiently dependable for the future as well as for the present.

The story of the writing of this treatise is as follows:

In the summer of 1916, when "Bridge Engineering" was issued, the author recognized that there was one very important bridge subject that he had not completely covered, viz., economics; and he thereupon listed ten major economic problems at that time unsolved, and came to the determination that they should no longer be left in that condition, if he could prevent it. After repeatedly failing to interest any other investigator in