Water, why does it expand when freezing, while bodies generally contract with cold and expand with heat, 341
Water, why does it never freeze to a great depth, 342
Water, how much deeper is it than it appears to be, 480
Water, why has the exceptional law, by which it expands when freezing, been ordained, 343
Water, why can we seldom succeed in the first attempt to touch anything lying at the bottom of, 481
Water, what causes it to flow from a pump, 651
Water, why does it run through a syphon, 655
Water, why does it become solid when it freezes, 751
Water, what proportion of the earth's surface is covered by it, 554
Water, why does it dissolve substances, 758
Water, why does hot dissolve more readily than cold, 759
Water, why is it difficult to wash in hard, 763
Waters, why are some impregnated with mineral matters, 767
Water, why does stagnant become putrid, 769
Water, is there danger attending drinking it on account of animalculæ, 770
Water, what are the means by which it may be purified, 771
Water, why will a drop upon the blade of a knife leave a dark spot, 777
Water, why does it roll in agitated globules when dropped upon hot iron, 796
Water, why is spring fresh and invigorating, 803
Water, why is boiled flat and insipid, 804
Weather, why does a yellow sunset foretell wet, 534
Weather, why does a red sunset foretell fine, 535
Weather, why does a red sunrise foretell wet, 536
Weather, why does a grey sunrise foretell dry, 537
Weather, barometrical indications of, 708
Whales, why have they a large development of oily matter about their heads, 1068
Whale, why has it feathery bones extending from its jaws, 1095
Whales, why are, their eyes provided with very thick coats, 1131
Wheat, why do the ears stand up by day and turn down by night, 1175
Wheat, what is the northern limit of, 1235
Wheat, why is silica diffused over its stem, 1261
Wheat-crops, why do they greatly exhaust the soil, 1263
Wick of a candle, why does it turn black as it burns, 225
Wick of a candle, why is there a spark generally at the end of it, 256
Winds, why are north usually cold and dry, 386
Winds, why do trade winds blow from east to west, 670
Winds, what determines the character of, 674
Wind-mills, why do their wings turn round, 690