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2. By Meridional Altitudes of the Sun, or a Star whose declination is
known, involving the Reduction to the Meridian.
6. By Transit Observations on the Prime Vertical
IV.-TO FIND THE LOCAL TIME.
TABLES OF USE IN THE FOREGOING PROBLEMS.
No. 4. CONTENT PLOT AND DIAGRAM-ditto.
-to face page 60. No. 6. ANAGLYPTOGRAPH ENGRAVING FOR TOPOGRAPHICAL DRAW
ING—to face page 117. No. 7. SPECIMENS OF THE VERTICAL AND HORIZONTAL STYLE OF
SKETCHING GROUND—to face page 59.
No. 8. METHOD OF TRACING CONTOURS
to face page 95, &c.
No. 9. SPECIMEN OF CONTOURING
AND 113 WOOD-CUTS.
The basis of an accurate survey, undertaken for any extensive geodesical operation, such as the measurement of an arc of the meridian, or of a parallel, or the formation of a geographical or territorial map, showing the positions of towns, villages, &c., and the boundaries of provinces and counties, or a topographical plan for military or statistical purposes, must necessarily be an extended system of Triangulation, the preliminary step in which is the careful measurement of a base line on some level plain :-at each extremity of this base, the angles are observed between several surrounding objects previously fixed upon as trigonometrical stations; and also, when practicable, those subtended at each of these points by the base itself. The distances of these stations from the ends of the base line and from each other are then calculated, and laid down upon paper, forming so many fresh bases from whence other trigonometrical points are determined, until the entire tract of country to be surveyed is covered over with a net-work of triangles of as large a size as is proportioned to the contemplated extent of the survey, and the quality and power of the instruments employed. Within this principal triangulation secondary triangles are formed, and laid down in like manner by calculation; and the interior detail is filled up between