Hadley's sextant, described, 137; its
adjustments, 139; its index error
determined, 140.
Herschel, his telescope, 84.
Horizon, artificial, 121.
Huyghens, his aerial telescope, 81;
his eye-piece, 82.
Land chain, 92.
Lenses, various forms of, and effects
produced by them, 70; their focal
lengths defined, 72; focal length
of a convex lens practically deter-
mined, 72; images formed by len-
ses, 73.
Level, spirit, 96; the Y level, 97;
its adjustments, 101; Troughton's
level, 104; Gravatt's level, 105;
water level, 112; reflecting level,
113.
Levelling staff, 104.
Levelling, remarks on, 106; for sec-
tions, 108; field-book, 109.
Light, pencils of, defined, 67; chro-
matic dispersion of, 72.
Linear measures, table of, 92.
Marquois's scales, 42.
Mean proportional found, 58.
Micrometer, 47.
Microscopes, refracting, described, 76;
their magnifying powers deter-
mined, 79; reflecting, described,
80; the reading microscope de-
scribed, 160; its adjustments, 161;
the solar microscope, 88.
Mirrors, glass, secondary images
formed in them, 75.
Mounting, varnishing, &c., paper and
drawings, 65.
Multiplication, 28, 56.
Parallax, of a telescope, 100; of a
sextant, 119.
Parallel lines drawn, 43.
Pen, drawing, 7; road, 8.
Perpendicular lines drawn, 44.
Plain scale, 33.
Plotting scales, 50, 133; sections,
111; a survey, 129.
Polygon, inscribed in a circle, 5, 40;
formed upon a given line, 40.
Pricking point, 8.
Prism, defined, 67; its effects upon
light explained, 68; its uses in
optical instruments, 69.
Prismatic compass, 115.
Proportion, 29, 36, 56.
Protracting scales, 14.
Protractors, upon plain scales, 33:
circular, 129; semicircular, 131.
Radius found, from the length of the
sine, tangent, or secant, of an arc,
42.
Ramsden, his eye-piece, 83.
Reflectors, plane, their effects and
uses in optical instruments, 74;
curvilinear reflectors, 75; methods
of forming and polishing parabolic
reflectors, 76, foot note.
Reflecting circle, described, 141;
directions for observing with it, 142.
Rhumbs, line of, 16, 17; sine rhumbs,
28; tangent rhumbs, 28.
Scales, of equal parts simply divided,
9; diagonal, 10; vernier, 11;
formed by sector, 38; of chords,
sines, versed sines, tangents, se-
cants, and semitangents, 14; of
rhumbs, chords, and longitudes,
15; of hour-lines and latitudes,
15; logarithmic, see Gunter's lines;
Marquois's, 42.
Screw, clamping, 47; tangent, 47.
Secant, to any desired radius, found,
Sextant, box, 117; Hadley's, 137.
Opera-glass, or Galilean telescope, 84. Sines, scales of, 14;
radius, found, 41; logarithmic, see
Gunter's lines, 25; sine rhumbs, | Tangents, scale of, 14; to any de-
Solid contents found, 30; of squared
timber, 60; of tapering timber, 59.
Sphere, its orthographic projection,
18; gnomonic projection, 19; ste-
reographic projection, 20; develop-
ment of a portion, 22; Flamstead's
projection, 23.
Spherical confusion of lenses ex-
plained, 72.
Spirit level, 96.
Square, of a number, found, 57;
root, 6; measures, table of, 93.
Station pointer, 135.
Superficies, or area, measured, 29.
Surveying, remarks upon, 126.
Tables, giving the correction to be
subtracted from the approximate
content of timber, as determined
by the sliding rule, 61; of dimen-
sions of drawing paper, 65; of
linear measure, 92; of square
measures, 93; showing the reduc-
tion in links and decimals of a link
upon 100 links for every half
degree of inclination from 3° to
20° 30', 95; showing the reduction
in feet and decimals of a foot upon
100 feet for each foot difference of
level, 110; of formulæ for deter-
mining the time, the latitude of
sired radius, found, 42; logarithmic,
27; tangent rhumbs, 28; tangent.
screw, 47.
Telescopes, refracting, astronomical,
81; with achromatic object glasses,
82; Galilean, or opera glasses, 84;
refracting, adjusted, and tested,
86; reflecting, why required, 84;
Newtonian, 84; Gregorian, 84;
Cassegrainian, 85; Herschelian,
85; reflecting, adjusted, and tested,
88.
Theodolite, described, 122; adjust
ments of horizontal limb, 125;
adjustments of vertical limb, 125;
surveying with, 127.
Transit instrument, described, 144;
its adjustments, 147; method of
making and recording observations,
151; use of the portable transit,
153.
Triangle, isosceles, having each of
the angles at the base double of
the third angle, constructed, 40;
right-angled, solved, 31.
Troughton, his level, 104; his reflect-
ing circle, 141.
place of observation, and the decli- Wholes and halves, 4.
nation of a heavenly body, from
observations made with the altitude
and azimuth instrument, 159.
ELLIOTT, BROTHERS,
30, STRAND, LONDON,
LATE 56, STRAND, AND 5, CHARING CROSS,
PHILOSOPHICAL INSTRUMENTS,
THE ADMIRALTY, ORDNANCE, EAST INDIA COMPANY,
AND MILITARY COLLEGES.
Prize Medal at the Great Exhibition of 1851.
Three Prize Medals at the American Exhibition of All Nations.
Ditto, 24-inch, with Circular Brass Portable Stand
Ditto, 30-inch, with Iron Stand
Large Transit Instrument, for Permanent Stations
Twelve-inch Azimuth, and Altitude Instrument
Fifteen-inch ditto, with Microscopes
Six-inch Circular Protractor, with Tangent Screw adjustment
Metal and Brass Circular and Semi-circular Protractors, 10s. 6d. to 5
Opisometer or Map Meter, for measuring curved lines
Pencil Cutter
Card Protractors
Amsler's Patent Planimeter, for calculating Areas with the
Sang's Platometer, for calculating areas on plans
St. John's Patent Ship Compass, for detecting local error of needle
Patent Portable Station Staves...
ELLIOTT, BROTHERS, in addition to the large Circular dividing Engine (which they purchased from Mr. JONES of Charing Cross) have received by order of Government, the straight line dividing Engine from the Admiralty.
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