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Striking differences between natural and artificial objects, 47.—

Numerous properties of ice, 48.-Its formation, 48.-Distri-

bution of heat, by radiation, conduction, and convection, 48.

- Expansion and contraction, 49. Maximum density of

water by cold, 49.-The freezing point, 50.-Expansion by

cold, 50.-Experimental illustrations, 50.-The process of

convection illustrated by the freezing of a lake, 52.-Lowering

of the freezing-point in still water, 52.—Heat of liquefaction,

53.-Why deep lakes freeze slowly or not at all, 53. —Freezing

of rivers-ground-ice, 53.-Freezing-point of salt water, 53.—

Expansion of water by cold-experimental illustrations, 54.

-Freezing, at the surface and at the bottom, 55.-Ultimate

effect of freezing at the surface, 56.-Maximum density of sea

water, 56.-Mechanical force of water in freezing, 58.-Dis-

integration of soils, rocks, and building stones, 59.-Brard's

method of detecting porous stones, 60.-Further illustrations

of the mechanical action of frost, 60.-Freezing of fish ponds,

61.-Making holes in the ice, 62.-Avidity for air varies in

different fishes, 62.-Supply of air to an aquarium, 63, note.—

Ventilation of frozen fish ponds, 1, by feeders, 2, by springs,

64.-3, by absorption of the soil and infiltration, 65.—Forma-

tion of cats' ice, 65.-Temperature of the water beneath the

ice, 66.-Frost smoke, 66.-Penetration of the soil by frost,

66.-Purity of ice, 68.—Water in freezing excludes foreign

matter, 68.-Burning lens of ice, 69.-Expansion and contrac-

tion of ice by variations in temperature, 70.-Colour of ice,

70.-Conduction of sound by ice, 70.-Specific gravity of ice,

71.-Latest determination of, 72.-Welding of pieces of ice

above 32° Fahr., 72.-Regelation, 74.-Experimental illustra-

tions, 75.-Ice of different fusibilities, 79.-Dr. Faraday's ex-

planation of, 79.-Dr. Tyndall's experiments on regelation, 81.

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