In preparing the manuscript for this book, the author's sole object has been to systematize and reduce to an exact basis, the principles that underlie the practice of plumbing. The necessity for accurate rules and formulas, instead of the empirical methods formerly em-ployed, was often and forcibly brought home to the author when designing plumbing installations for large buildings. The scarcity of scientific information on this important branch of sanitation was quite marked. No book had ever been published that indicated the best kind of material to use for a given purpose, that told how work should be designed and installed to be perfectly sanitary, and that showed how to proportion the various parts with relation to the whole, so that a plumbing system designed and installed according to the text would give perfect service.

Rules and formulas for proportioning hot and cold water supply pipes were entirely lacking and no literature was available that would be of assistance in determining this most important feature of a building. Neither could anything be had that would indicate the size of piping required to supply a given number of flushing valves for closets, nor that mentioned the numerous other conditions requiring consideration when designing a plumbing installation.

Realizing this, the author gathered much valuable data and worked out many rules and formulas from his private practice, and the gist of the rules, formulas and data have been incorporated in "Principles and Practice of Plumbing" where, for the first time, they were offered to the public.

In planning the scope of the book, it was assumed that the reader knew but little of the subject of plumbing, and had no source of information outside of the book. With this premise in mind an effort was made to prepare the subject matter so clearly and concisely that a person of average intelligence, by following the text, could design and proportion any plumbing installation. That this object has in a measure been realized is evidenced by the interest of architects, engineers and plumbers in the articles when they first appeared in serial form in Modern Sanitation, and by the large domestic and foreign advance subscription for the work in book form.

It is the intention of the author and publishers to keep "Principles and Practice of Plumbing" the standard work on plumbing and sanitation, and to this end the book will be subject to revision when found necessary. Criticism of the subject matter will be welcome, as by fair and intelligent comment its value will be enhanced.

J. J. Cosgrove

Scranton, Pennsylvania

December 15, 1906 vi