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By J. BUTLER WILLIAMS C.E. F.G.S.

AUTHOR OF A MANUAL OF MODEL DRAWING AND PERSPECTIVE'

THE THIRD EDITION

LONDON

JOHN W. PARKER AND SON WEST STRAND

LONDON:

PRINTED BY WERTHEIMER AND CO.,

FINSBURY CIRCUS.

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PREFACE TO THE FIRST EDITION.

I

HAVE employed the term 'Geodesy' as one well suited by its comprehensive meaning to embrace the various subjects treated of in the present work; and, by adding the word 'Practical,' I have designed to indicate, that actual practice in the field is the especial object I have had in view. This has not been lost sight of throughout the work, and the subject has been so arranged as to enable the student, at the outset, to commence a simple survey, minute practical directions being given to guide him in each new process, or to prepare him to surmount, by his own judgment, difficulties which may arise under an unforeseen aspect.

Proceeding through the elementary processes, the student is brought, by regular gradations, to understand the principles, and to appreciate the bearings of the more perfect methods which the demands of an advanced state of civilisation render it necessary to employ, in order to ensure that degree of accuracy which is now deemed essential.

In the Chapter on Trigonometrical Surveying, I have taken the opportunity of making the student acquainted, by a description of some of the interesting trigonometrical operations of this and other countries, with the highly scientific processes

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