explained, 74.

Achromatic eye-piece, 76.

Aerial telescope, 85.

Altitude and azimuth instrument,
description of, 163; adjustments of,
166; use of, 167.

Angles, methods of setting off, 17,41;
measuring, 17.

Area, of a drawing, reduced or en-
larged, 54; of a board or plank
found, 61; of a survey computed,

141.

Artificial horizon, 128.
Astronomical triangle, 168; table of
formulæ connecting the parts of,
169.

Bench marks, 117.

Bisection of a straight line, 39.
Bow compasses, 4.

Box sextant, described, 123; its pa-
rallax explained, 125; and elimi-
nated, 127.

Camera obscura, 94; lucida, 95.
Casini, his aerial telescope, 85.
Cassegrainian telescope, 88.
Chains, Gunter's and land, 97.
Chords, line of, constructed, 15; uses
of, 17.

Chromatic dispersion of light ex-
plained, 75.

Clamping screw, 49.
Collimation, line of, 105.

Collimator, description of, 172; use
of, 173.

Compasses, 1; beam, 50; bow, 4;
hair, 2; with moveable points, 3;
proportional, 4; triangular, 7.
Compass, prismatic, 121.

larged, 6; solid, measured, 31.
Copying drawings, 54.

Course, method of setting off a, 17.
Crystals measured, 178.
Cube root, extraction of, 7.
Cylindrical vessel, its content in gal-
lons measured, 64.

Development of a portion of a sphere,
23.

Diagonal scale, 11.

Dial, horizontal, 25; erect south, 26;
east and west, 26.
Dip sector, 153.

Division, arithmetical, 30, 58; of a
line into equal parts, 39.

Drawing, a, its linear dimensions re-
duced or enlarged, 5, 41, 53, 55;
its area reduced or enlarged, 5; its
solid content reduced or enlarged, 6.
Drawing-paper, management of, 66;
dimensions of, 67.
Drawing pen, 7.

Edge, straight, 9.

Equal parts, scales of, 10.

Eye-piece, celestial negative, 85;
positive, 86; terrestrial, or erect,
87.

Flamstead's projection, 24.

Geometrical construction, general
rules, 68.
Gnomon, 26.

Gnomonic projection, 20.

Goniometer, common, 175; Wollas-
ton's, 176.

Gravatt, his adjustment of the level,
108; his level, 111.

Gregorian telescope, 88.
Gunter's chain, 97; Gunter's lines,
their construction, 27; their use,
29.

Hadley's sextant, described, 144; its
adjustments, 147; its index error
determined, 148.
Herschel, his telescope, 89.
Horizon, artificial, 128.
Huygens, his aerial telescope, 85;
his eye-piece, 85.

Land chain, 97.

Lenses, various forms of, and effects
produced by them, 73; their focal
lengths defined, 75; focal length
of a convex lens practically de-
termined, 75; images formed by
lenses, 76.

Level, spirit, 101; the Y level, 103;
its adjustments, 107; Troughton's
level, 110; Gravatt's level, 111;
water level, 119; reflecting level,
120.

Levelling staff, 109.

Levelling, remarks on, 112; for sec-

tions, 114; field-book, 115.
Light, pencils of, defined, 70; chro-

matic dispersion of, 75.
Linear measures, table of, 100.

Marquois's scales, 45.
Mean proportional found, 60.
Micrometer, 49.

Microscopes, refracting, described, 79;
their magnifying powers deter-
mined, 83; reflecting, described,
83; the reading microscope de-
scribed, 170; its adjustments, 171;
the solar microscope, 93.
Mirrors, glass, secondary images
formed in them, 78.
Mounting, varnishing, &c., paper and
drawings, 67.
Multiplication, 30, 58.

Newtonian telescope, 88.
Numbers, line of, 27.

Offsetting staff, 101.

Opera-glass, or Galilean telescope, 87.
Orthographic projection, 19.

Pantagraph, 52.

Parallax, of a telescope, 106; of a
sextant, 125.

Parallel lines drawn, 46.
Pen, drawing, 7; road, 8.
Perpendicular lines drawn, 46.
Plain scale, 35.

Plotting scales, 51, 140; sections,
118; a survey, 136.

Polygon, inscribed in a circle, 5, 42,
43; formed upon a given line, 42.
Pricking point, 8.

Prism, defined, 70; its effects upon
light explained, 71; its uses in
optical instruments, 72.
Prismatic compass, 121.
Proportion, 31, 38, 58.
Protracting scales, 15.
Protractors, upon plain scales, 35;

circular, 136; semicircular, 138.

Radius found, from the length of the
sine, tangent, or secant, of an arc,
44.
Ramsden, his eye-piece, 86.
Reflectors, plane, their effects and
uses in optical instruments, 77;
curvilinear reflectors, 78; methods
of forming and polishing parabolic
reflectors, 79, foot note.
Reflecting circle, described, 149;
directions for observing with it, 150.
Rhumbs, line of, 16, 17; sine rhumbs,
29; tangent rhumbs, 29.

Scales, of equal parts simply divided,
10; diagonal, 11; vernier, 12;
formed by sector, 40; of chords,
sines, versed sines, tangents, se-
cants, and semitangents, 15; of
rhumbs, chords, and longitudes,
16; of hour-lines and latitudes,
16; logarithmic, see Gunter's lines;
Marquois's, 45.

Screw, clamping, 49; tangent, 49.
Secant, to any desired radius, found,
43.
Sector, 36.

Sextant, box, 123; Hadley's, 144.
Sines, scales of, 15; to any desired
radius, found, 43; logarithmic, see
Gunter's lines, 28; sine rhumbs,

29.

Sliding rule, 57.

Solid contents found, 31; of squared
timber, 61; of tapering timber, 64.
Sphere, its orthographic projection,
19; gnomonic projection, 20; ste-
reographic projection, 21; deve-
lopment of a portion, 23; Flam-
stead's projection, 24.
Spherical confusion of lenses ex-
plained, 75.
Spirit level, 101.

Square, of a number, found, 59;
root, 6; measures, table of, 100.
Station pointer, 143.
Superficies, or area, measured, 31.
Surveying, remarks upon, 133.

T square, 138.

Tables, giving the correction to be
subtracted from the approximate
content of timber, as determined
by the sliding rule, 63; of dimen-
sions of drawing paper, 67; of
linear and square measures, 98;
showing the reduction in links and
decimals of a link upon 100 links
for every half degree of inclination
from 3° to 20° 30', 100; showing
the reduction in feet and decimals
of a foot upon 100 feet for each
foot difference of level, 116; of
formulæ for determining the time,
the latitude of place of observation,
and the declination of a heavenly
body, from observations made with
the altitude and azimuth instru-
ment, 169.
Tangents, scale of, 15; to any de-

sired radius, found, 43; logarithmic,
29; tangent rhumbs, 29; tangent
screw, 49.
Telescopes, refracting, astronomical,
84; with achromatic object glasses,
85; Galilean, or opera glasses, 87;
refracting, adjusted, and tested,
89; reflecting, why required, 87;
Newtonian, 88; Gregorian, 88;
Cassegrainian, 88; Herschelian,
89; reflecting, adjusted, and tested,
92.
Theodolite, described, 129; adjust-
ments of horizontal limb, 131;
adjustments of vertical limb, 132;
surveying with, 134.

Transit instrument, described, 154;
its adjustments, 157; method of
making and recording observations,
161; use of the portable transit,
162.

Triangle, isosceles, having each of
the angles at the base double of
the third angle, constructed, 43;
right-angled, solved, 32.
Troughton, his level, 110; his reflect-
ing circle, 149.

Vernier, described, 47; scale, 12.
Versed sines, scales of, 15.
Vision by means of lenses, 73.

Wholes and halves, 4.

Y level, 103.