Geographer, United States Geological Survey; Member American Society of Civil Engineers;
Author of a "Manual of Irrigation Engineering," etc.

FIRST EDITION.

FIRST THOUSAND.

NEW YORK:

JOHN WILEY & SONS.

LONDON: CHAPMAN & HALL, LIMITED.

PREFACE.

THIS book has been prepared with a view of bringing together in one volume the data essential to a comprehensive knowledge of topographic surveying. It has been my aim to cover the varied phases of all classes of surveys which are made with a view to representing on maps information relative to the features of the earth's surface. The methods elaborated are chiefly those which have been developed in recent years by the great government surveying organizations and by such few private corporations as have kept in touch with the most modern practice; but I have endeavored to go beyond these, and, guided by personal experience, to adapt them to the most detailed topographic as well as to the crudest exploratory surveys. The hope is entertained, therefore, that the engineer who may be called upon to conduct an exploratory survey in an unknown region, or to make a detailed topographic map as a preliminary to construction, will find herein descriptions and examples of the methods he should employ, the essential tables for the computation of his results, and hints which will guide in the equipment of his party.

I have sought to avoid any detailed description of those instruments or methods which are elaborated in works on general surveying. The volume is devoted practically to higher surveying, and presupposes a knowledge of all the more elementary branches. At the same time, many of the

subjects treated are essentially elementary, and these are briefly described, in order that all the facts which the topographer must know and all the formulas and tables which he must have at hand in the field may be brought together. An effort has been made to present the subject in the most practical form. Accordingly, care has been taken to avoid an elaboration of the mathematical processes by which the various formulas have been derived, as they are to be found in detail in several well-known treatises to which textual reference is made. To give more immediate aid to the working surveyor, examples of the various computations are presented, as are illustrations of the instruments, methods, and resulting maps from surveys actually executed.

The mode of presentation is not that usually followed in such works. Instead of describing the instruments or their uses independently, each is described in that portion of the text in which its employment in field surveying is most prominently mentioned. The tables are not brought together at the end of the volume, but each is placed in that portion of the text which relates to its use. The object is to produce a handy reference-book for use in the field, as well as a text-book for guidance in college instruction. It is believed that, by this arrangement, if a topographer in the midst of his field-work desires information on a special point, it can be found, with accompanying examples and tables, gathered together in one chapter or clearly indicated by cross-references. Again, the method of treatment usually followed in works of this class consists in, first, a description of the astronomic methods on which general map surveys must be based, and then a description of primary triangulation as a basis for the detailed topographic surveys which are finally described. I have reversed this order and have adopted the more natural method. of commencing with the simplest operations and advancing gradually towards the most complex and refined. Each subject is treated in the same manner. It is believed that the