The devotion of an entire chapter specifically to the conclusion of an engineering treatise is somewhat of an innovation in technical literature, and, therefore, demands an explanation for its intrusion. The essential reason is that this is to be the author's last technical book, excepting only that after the third thousand of his "Bridge Engineering," now on sale, is exhausted, he intends to write for the second edition thereof an "Appendix" to cover the results of all bridge investigations, other than economic, which he has made (or shall have made) since that work was first issued in the summer of 1916.

The reasons why, after thirty-seven years of rather desultory book-writing, he is about to desert the field of technical literature, or, strictly speaking, that portion of it which pertains to the preparation of formal treatises, are the following:

First. In many cases the writing of technical works is an extravagant indulgence that very few engineers can afford; for not only does it necessitate the expenditure of a large amount of cold cash to prepare the manuscript of any book worthy of being considered real engineering literature, but, even after it is finished, an author sometimes has to provide all the money required for publication; the publisher deeming the many years spent and the great outlay of money used in building up the means for placing such works on the market a fair equivalent for that spent in preparing the manuscript. This is specially true in scientific books which require special means and careful study to put them properly before those they are written for.

Second. The amount of personal time that one must devote to the preparation of the MS. of any engineering work which aims to offer mainly original material, and is not, like many engineering books, a mere compilation of data gathered from standard treatises and the technical press, is simply appalling; and the diversion of such time from his professional practice is often a serious menace to the success of an engineer's business.

Third. The author feels that in presenting this treatise on bridge economics to the profession, in addition to his seven preceding books and numerous technical memoirs, he shall have almost exhausted all that he has to say in print on the subject of his chosen specialty. In other words, his message to the younger generation of engineers shall have been delivered; and  he  should  then,  with  a  clear  conscience  about  having  "done

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