Outline of the Method of Conducting a Trigonometrical Survey, for the Formation of Topographical Plans

Of the extensive and scientific Geodesical Operations
described in these latter works, the present Treatise pro-
fesses to give nothing beyond a brief outline, as their
detailed account would be far too voluminous to be con-
densed in so small a compass.

The cadets at Woolwich and Addiscombe are taught the
use of the Chain and Theodolite; and to calculate the
contents of the different portions into which the ground is
divided by natural and artificial boundaries; they are also
rendered conversant with Plane Trigonometry and Mensu-
ration, and with sufficient Spherical Trigonometry for the
solution of the ordinary cases of Spherical Triangles.
Such preliminary knowledge is consequently assumed as
being already acquired. It is, however, in the

power
individual to make himself master of the necessary theore-
tical part of this knowledge, by the study of one or other of
the numerous excellent works on Trigonometry and Mensura-
tion ; and the practice of Land Surveying can be acquired in
a few weeks in the Field, under any competent Instructor,
or even without this assistance, by the careful study of some
elementary work on the subject.

of any

Royal Engineer Establishment, Chatham.

1839.

TABLE OF CONTENTS.

CHAPTER I.

Page

GENERAL OUTLINE OF THE SYSTEM OF CARRYING ON A TRIGONOME-

TRICAL SURVEY..

1

CHAPTER II.

MEASUREMENT OF A BASE LINE.-Description of the different Methods

that have been adopted to ensure its Correct Measurement.-Combined

Iron and Brass Rods used by Colonel Colby, on the Ordnance Survey

of Ireland, with the Method adopted to obtain a Visual instead of an

Actual Contact by means of Reading Microscopes—Reduction of a

Base Measured on any Elevated Plain to its value at the Level of

the Sea-Prolonging and verifying a Measured Base by Triangulation. 4

CHAPTER II.

TRIANGULATION.—Choice of Stations-Method of rendering Distant

Stations Visible by Reflection of the Sun's Rays, and by Argand

Burners-Drummond's Light-Method of Increasing the Length of the

Sides of the Triangles directly from the Measured Base-Secondary

Triangles—Assumed Base-Instruments used for Observing Angles on

the Continent and in England—Reduction to the Horizon—Spherical

Excess—Reduction to the Centre-Adjustments of a Theodolite-

Advantages of Repetition-Col. Colby's Method of Discovering Lost

Stations—Method of laying down the Triangulation-Position of Stations

also ascertained by Astronomical Observations

12

CHAPTER IV.

INTERIOR FILLING-IN OF SURVEY, EITHER ENTIRELY OR PARTIALLY,

BY MEASUREMENT. SECTION 1st.-Method of Filling-in the Detail

entirely by Measurement, as Practised on the Survey of Ireland-

Levelling Marks and Form of Levelling Field-Book, and Register

for Horizontal and Vertical Distances-Measurement of Roads with

the Chain and Theodolite-Method of Computing the Contents of the

various Enclosures directly from the Field-Book, and Form of Content

Register-Hints on Filling-in the Detail of a Survey. SECTION 2nd.-

Filling in the Interior, partly by Measurement, and partly by Sketching,

as was practised on the Ordnance Survey of England-Road Surveying

-Variation of the Compass-Method of Sketching between Tri-

gonometrical Points, and Measured Lines - Instruments used in

Sketching-Practical Methods of avoiding Obstacles and Determining

In-accessible Distances in the Field

Military RECONNAISSANCE AND Hints ON SKETCHING GROUND-

Particular Objects of a Reconnaissance under Different Circumstances,

Method of Commencing Military Sketch-Portable Instruments best

adapted for Sketching-Methods in Use for Delineating Ground with

a Pen

or Pencil-Vertical System-Horizontal-Description of the

Method of Major Lehman of giving a Mathematical Representation of

the Slopes of the Ground by a Scale of Shade-Colonel Van Gorkum's

Improvement upon this System by Substituting Contour lines at

Equal Vertical Intervals, and “normals” between these Contour Lines

in the Direction of the Slopes of Greatest Inclination ; from the length

of which, Measured on a Scale, the Angle of Inclination of the Slope

can be obtained. French System of Horizontal Contours only— Paste-

board Clinometer for Measuring Slopes—Hints to Assist in Sketching

Ground-Description of the “ Telegoniomètre” for Measuring Angles

and Distances—Military Reconnaissance of an Enemy's Works-Con-

ventional Signs

CHAPTER VI.

SHADING ENGRAVING TOPOGRAPHICAL PLANS.- Vertical Dis-

position of Light-Oblique Light, and the Objections to this Method-

Conventional System....

69

CHAPTER VII.

LEVELLING.–Levelling for Sections-Correction for Curvature-

for Refraction-Average Amount of these Corrections—Reciprocal

Angles of Depression and Elevation for Determining the Amount

of Refraction at any particular period—Method of Taking Sections

of Ground with a Theodolite-Cross Sections—Trial Sections-Check

Levels-Spirit Level, its Adjustments-French Water Level-Boning

Rods—Reflecting Level-Method of Levelling with the Spirit Level,

or any Instrument adapted for Tracing Horizontal Lines—Tracing

Contour Lines for Plans of Comparison ---Plotting Sections-Sectio

Planography-Prismoidal Formula...

72

CHAPTER VIII.

Mountain BAROMETER.—Method of ascertaining Altitudes with the

Mountain Barometer Substitute for the Barometer - Determining

Altitudes by temperature of boiling water

AND

97

CHAPTER 1X.

GEODESICAL OPERATIONS CONNECTED WITH A TRIGONOMETRICAL SUR-

VEY-Figure of the Earth-Measurement of an Arc of the Meridian-
Standards of Weight and Measure obtained from the Measurement of
an Arc of the Meridian between Dunkirk and Barcelona, detailed in
the “ Base du Système Métrique Décimal”—Popular Account of the

Page

Method of Conducting these Measurements—Distances between Two

Points whose Latitude and Longitude are known — Convergence of

109

Meridians-Variation of Compass-Projections of the Sphere

CHAPTER X.

PRACTICAL AstroNOMY.-Sextant and Repeating Circle-Definitions.

PROBLEMS.

1. To convert Sidereal Time into Mean Solar Time, and the reverse 137

Il. To determine the several corrections for Refraction, Parallax, &c. 139