96;
experiments with, 301-304*;
one of chief elements in fuel, 315-316;
part taken by, in burning, 312-319.

Ice, slight friction of, 52*;
action of molecules in, on freezing and melting, 96-97;
reason for floating of, 98-99.

Incandescence, defined, 125.

Incandescent lamps, 125-126;
number of electrons in, 197;
working of, 229-232.

Inertia, 66-71;
definition of, 70.

Insulators, of heat, 118;
of electricity, 213;
substances used as, 215.

Iodine, an element, 299;
testing with, for starch, 373-374.

Iron, a good conductor of heat, 118;
an element, 299.

Irons, electric, 229*, 230, 232.

Iron salt, formed by lemon juice on steel, 353.

Iron ships, reason for floating, 24*-26.

Kerosene, boiling of, 112;
distilled from petroleum, 114;
carbon and hydrogen in, 315.

Laughing gas, 309.

Lava in volcanoes, 110.

Lead, an element, 299.

Lead pencils, arc light from, 233*-234*.

Leaning Tower of Pisa, 29*-30.

Lemon juice, action of, on silver and on steel, 353;
litmus test of, 359.

Lens, of eye, 142, 151*-153;
of camera, 143, 149*, 328;
convex, 148-149;
concave, 149*;
in telescope, 157.

Levers, 57-65*.

Light, radiation of, 122, 123*-128;
reflection of, 129-135*;
refraction of, 136*-141;
focus of, 142-149*;
brought to focus by convex lens, 149;
diffusion of, 158-161*;
color a kind of, 162;
speed of, 182;
chemical change caused by, 326-335;
and manufacture of food in plants, 332-333.

Lightning, cause of, 200-201.

Limewater test for carbon dioxid, 375*-376.

Liquid air, 97, 112.

Liquids, absorption of, 36-40;
diffusion in, 272.

Litmus paper, experiments with, 358-359.

Litmus test, the, 358-359.

Lye, a common base, 356;
experiment with, 356;
soap made from, 357;
used for clearing out drainpipe, 358;
neutralization of, by acids, 363.

Machinery, oiling of, to decrease friction, 53-54.

Magdeburg hemispheres, 15, 16*-17.

Magnetism, 190 ff.

Magneto, of automobile, 210, 211*;
of old-fashioned telephone, 210-211.

Magnets, 190-195*.

Magnification, 150-157;
by concave mirror, 157.

Magnifying glass, convex lens in, 149;
operation of, 150-156*.

Manganese dioxid, an essential in explosives, 347.

Megaphone, working of, 184.

Melti