PREFACE ΤΟ THE SECOND EDITION. THE first edition of this work originated in the wants of the Gentlemen Cadets in 1813 and 1814: more was added as it became requisite, the advantage of which was very apparent, as from each reading the manuscript their instruction was rendered more uniform, and much time was saved by this means. An officer who had not studied at the Senior Department complaining to the author of the incovenience he experienced when having occasion to find the latitude, variation of the needle, &c., abroad, with such instruments as he could get, and without any previous knowledge of the subject, a little was added on practical astronomy, not by any means with an intention of substituting it for the more correct observations and rules of other works. The first publication came out, after numerous solicitations, in 1839. In the present edition much has been added that may be useful. In the former, levelling was not very fully explained: but it has now become so necessary to many persons, and the methods and instruments are so much improved, as to require further illustration: this has accordingly been done. ROYAL MILITARY COLLEGE. PREFACE ΤΟ THE FIRST EDITION. THE following pages are intended to facilitate the acquisition of an art now becoming daily more important; and it is hoped that the student who is well grounded in the elementary parts of mathematics will find himself provided with a complete set of instructions in the following work. The nature of the work being entirely practical, and not entering into those niceties which characterise geodesical measurements, we have not begun with them, but beg leave to recommend the student to a perusal of the elaborate and highly interesting works, both English and foreign, upon that subject. Our object being to take up the business where geodesia* ends, requires only a good application of more simple instruments; yet as a survey or sketch may sometimes be required of sufficient extent to • Some formulæ upon this subject will be found at the end, by Mr. G. W. Hearn, B. A., of Cambridge, which he has kindly supplic d. render triangulation necessary, we have given some practical hints upon it. It was originally intended only to form a set of instructions for military sketching; but upon consideration it was thought better to begin by surveying, as the principles of the former are derived from the latter, and the work would thereby become more generally useful. From a conviction that the mere writings of the closet only tend to deceive the pupil, we have inserted original examples; thinking it better to state the thing fairly, than to use such as are constructed on purpose to agree with mathematical solutions. We desire to show what may be expected, and to guard the pupil against a very common supposition, namely, that when he is provided with instruments and books his work is half finished. The various tables to be used in the geographical approximations are contained in the Nautical Almanack and other works, indispensably necessary to a traveller who intends to collect them. It is a matter of much regret that we cannot produce drawings of a complete set of specimens of the great geological features of the earth; but they are chiefly contained in plans carefully lodged in the different government depôts, where, being connected with fortification, or other national works, it would be highly improper to submit them to in |