Aberration of thickness of lenses, 42;
spherical, in lenses and mirrors, 55;
wholly effaced, 58; chromatic, 59.
Absolute refractive power, 17; remains
constant, 17.

Accidental colours, 127.

Actinic influence of the solar spectrum,

90; of chemical rays, 218.

Action of light on plates of copper
covered with certain deposits of silver,
89.

Adaptation of the eye to different dis-
tances, 125.

Adiathermic bodies, 89.

Advantage of projecting rays through
lenses, 35.

to commerce from Fresnel's
lighthouse system, 228.
Agate, curious property of, 112.
Albumen in the eye, 117.

Alhazen's description of the eye, 4;

treats of vision, 4; the crystalline
humour, its principal use, 4; he did
not consider it a lens, 4.
American solar camera, 162.
Analysis of light, 67.

of sugar by polarised light, 112.
Anastatic process, 213.
Angle of polarisation, 108.
Anorthoscope, 210.

Anterior chamber of the eye, 116.
Aperture of diaphragm, how it affects
the intensity of photographic pictures,

145.
Aplanatic lens, 60; Dallmeyer's, 161;
most perfect copying-lens extant, 161;
double the intensity of the orthoscopic,
162.

Aqueons humour, 117.

Archimedes burnt the Roman fleet by
mirrors, 4.

Architect, the knowledge of optics useful
to the, 221.

Architecture enriched by photography,
89.

Argand lamps and paraboloidal reflectors
first introduced into lighthouses, 222.

Baptista Porta invents the camera ob-
scura, 5; he is mistaken concerning
the cause of single vision with two
eyes, 6.

Beautiful forms produced by the kaleido-
scope, 200.

phenomena exhibited by trans-
mitting polarised light through crys-
tals, 112.

Beauty of Fresnel's apparatus as im-
proved by Stevenson, 224.

Becquerel's experiments, 90.
Berard's discoveries, 88.
Bernard's views, 74.

Binocular telescope, 196.

Bi-unial dissolving-view apparatus, 141.
Blair's, Dr., discoveries, 84.

Borda first introduces Argand lamps and
paraboloidal reflectors into lighthouses,

222.

Canada, primeval forests of, 220.
Cassegrainian telescope, 53.
Catoptric light of Isle of May converted
into a dioptric light, 223.
Catoptrics explained, 42.

Caustic curves formed by reflection, 61;
discovered by Tschirnhausen, 62; in-
vestigated by M. de la Hire, James
and John Bernoulli, and others, 62;
cusps, 63.

figures, formed by a wash-hand

basin, 65.
Caustics formed by a china bowl, 64.
formed by refraction, 65.
Centre of visible direction, 121.
Change of refractive power in gases, 17.
Chemical influence of the spectrum, 89.
Choroid coat, 114.

Chromatic aberration, 59; how remedied,
145.

Ciliary processes, 117.
Coddington lens, 173.
Colour-blindness, 125.

Colours produced by intermixtures of
light and shade, 76; colours in art,
harmony of, 131.

Combination of colours, 129.

Combined effects of inflection and inter-
ference, 100; examples of, 100.
Common cress, experiments on its ger-
mination, 218.

Complementary colours, 127; how to
find, 129.

Compound microscope, 174; conditions
of efficiency, 176.

Concave speculum for lighting Druidic
fires, 4; of reflection from, 44.

and convex lenses remedy de-
fective vision, 5.
Concavo-convex lens, 19.
Condenser, 162.

Conditions of single vision with both
eyes, 123.

Conical reflectors, 54.

Conjugate foci, 31; correspond to the
positions of image and object, 37.
Contraction of the pupil of the eye, 6.
Converging rays, 31, 34; reflection of, by
concave and convex mirrors, 49.
Convex speculum, reflection from, 44.
Cornea, 114; projects outwards, 115; of
nearly uniform thickness, 115; form of
a common watch-glass, or concavo-
convex lens, 115.
Crystalline lens, 116.
Curvature of the field, 42.
Cylindrical reflectors, 54.

Daguerre's discovery, 89; daguerreo-
types, 89.

Dallmeyer's wide-angle rectilinear lens,
156; diffusion of definition obtained
by, 160; never obtained before, 160;
possesses great equality of illumina-
tion, 161; free from distortion without
diaphragms, 161; adapted for portraits,
views, and other pictures, 161.

Examples of the effects of inflection and
interference of light, 100.

Expansion of the pupil of the eye, 6.
Experiments on complementary colours
with wafers, 127.
by Mr. Robert Hunt on the
germination of seeds, 218.

by Drs. Daubeny and Gard-

ner, 219.
Extraordinary law of refraction, 105.
ray refracted from the axis
in some crystals, while in others it is
refracted towards the axis, 105.
Extreme red ray of the spectrum, 70.
Eye, 113; front view of, 113; vertical
section of, 113; sclerotic coat, 114;
choroid, 114; cornea, 114; retina, 114;
eyelids, 117; eyebrows, 117; achroma-
tic, 122; aplanatic, 122; wonderful
power of the eye, 127.

Faraday's system of ventilating light-
houses, 227.

Fata morgana explained, 25.
Feathers, iridescence of, 102.

Fifty photographs produced at the same
time, 161.

Flare in photographic pictures, 156.
Flint glass for telescopes, 84.

Fluorescent ray of spectrum, 70.

Focal length of the eye, 118.

Foci, conjugate, 31.

Focus of parallel rays, 28.
virtual, 47; principal, 47.
prevented being

Foliage of plants

scorched, 221.

Foramen centrale, 115, 123.

Formation of images by plane, concave,

and convex mirrors, 50.
Fracture in the negative prevented, 146.
Fraunhöfer's spectrum, 68.

French Government has adopted the
polarising saccharometer, 113.
Fresnel investigates diffraction, 97;
measures waves of light, 99; invents
the dioptric system of illuminating
lighthouses, 222; advantage to com-
merce of his lighthouse system, 228;
Stevenson's modification, 223.

Images, distortion of, 40.

formed by plane, convex, and
concave mirrors, 50-52.
Improvements in refracting microscopes,
176.

Inability of some persons to distinguish
colours, 123.

Incidence, angle of, 11.

Increasing density of the crystalline to-
wards its centre, 122.
Indices of refraction, 13.
Inflection of light, 96.

Influence of the spectrum on twenty-nine
different mineral and vegetable prepa-
rations, 90.

of the solar rays on the growth
of plants, 218; on the formation of
woody fibre, 220.

Innumerable axes of double refraction,
105.

Intensity of images depends on aperture
of diaphragm, 145.
Instruments, optical, 131.

Iridescence of mother-of-pearl, soap-
bubbles, feathers, &c., 102.
Iris, 115; grey, hazel, blue, or black, 115;
gives character to the eye, 115.
Irrationality of dispersion, 81.

Jansen invents the telescope, 6; first
made by him in 1590, and presented to
Prince Maurice of Nassau, 6; ineffec-
tual attempts to keep the invention a
secret, 6.

Juice of the ten-weeks stock, remarkable
actinic influence on, 90.

Kaleidoscope, 200; varieties of form,
202.

Kepler discovers the formation of the pic-

tures or images of external objects on
the retina, 5; he suggests improve-
ments in the telescope, 7; and scienti-
fically explained its principles, 7.
Kinnaird Head, Scotland, lighted with
paraboloidal reflectors and Argand
lamps, 222.

Kinnear camera, 169.

Kircher invents the magic lantern, 6.

Law of interference, 98.

of reflection, 43.

of visible direction, 119.

Lenses, forms of, 18; how they magnify
objects, 38; of least spherical aberra-
tion, 57; gem, 60; aplanatic, 60; or-
thoscope, 152.
Lieberkuhn, 183.

Light, its nature, 1; seientific men di-

vided in opinion respecting it, 1; useful
properties of, 2; Mosaic history of, 2;
homage rendered to its source, 2; Pla-
tonists acquainted with two of its
important properties, 3; reflection of,
42; waves of, how measured, 92; table
of undulations of, 95; inflection or dif-
fraction of, 96, 97; double refraction

and polarisation of, 102, 106; oxycal-
cium, 140; electric, 141; rays of, essen-
tial to the formation of woody fibre,
219; laws of, applied to the laying of
submarine electric cables, 221.

Light, heat, and actinism distinct solar
emanations, 89.

Lighthouse apparatus, trial of, at the
Paris Observatory, 224.

system of France, 225.
Lighthouses, illumination of, 222.
Limits of possible transmission, 24; table
of, 25.

Linear magnifying power, 172.
Long-sightedness, 5, 131.

Maximum actinic influence of the juice
of the ten-weeks stock, 90.

Meagher's binocular camera, 168; new
folding camera, 169.

Measure of dispersive power, 78.
Membrane of the aqueous humour, 117.
Method of lighting the sacred fires of the
ancient Romans and Druids, 4.
Microscopes, 171; refracting, 174; magni-
fying power of, 175; reflecting, 175;
Smith and Beck's popular, 176; direc-
tions for use, 178; binocular, 182; ap-
plication of polarised light to, 186; the
live box, 188; the glass trough, 188;
various forms of, 190.

Mirage explained, 26.

Mirrors, plane, concave, and convex, 43;
reflections from, 46; conical and cylin-
drical, 54.

Mosaic history of light, 2.
Mother-of-pearl, iridescence of, 102.
Muscles of the eye, 114.

Nasmyth's telescope, 196.

National manuscripts, how photo-zinco-
graphed, 215.

Near sight, or short sight, 132.

Negative axis of double refraction, 105.
or left-handed circular double
refraction, 106.

Newton's spectrum, 68; method of mea-
suring a wave of light, 92; telescope
preserved in the library of the Royal
Society, 193.

Number of waves of light in an inch, 94.

Objections to the use of large lenses for
photographic purposes, 37.