The Reason Why. Robert Kemp Philp

why have those with large trunks a great number of leafy branches, 1274

       Trees, why have poplars comparatively few leaves, 1275

       Trees, why had the mammoth comparatively few leaves, 1276

       Trees, why have oaks an abundance of leaves, 1277

       Trees, why are their trunks generally round, 1278

       Twilight, what is the cause of, 482

       Vacuum, what is a, 649

       Vacuum, is it possible to obtain a perfect, 650

       Vegetables, have they any heat, 90

       Vegetable structures, of what do they consist, 1151

       Vegetables, why do farmers sow different crops in rotation, 1164

       Vegetables, why are the hearts of cabbages, &c., pale yellow, 1182

       Vegetable productions, why are they so widely diffused, 1189

       Vegetable eaters, why do they feed so continually, 1091

       Vegetation, geographical distribution of, 1208

       Vegetation, what are the characteristics of tropical, 1218

       Vegetation, what are the changes in on quitting the tropics, 1232

       LESSON LXXIV.

       Vegetation, what are the characteristics of, upon approaching the polar zones, 1234

       Vegetation, what are the characteristics of mountain, 1238

       Vines, where are their favourable climates, 1233

       Walking, why does it make us warmer, 26

       Water, what becomes of that formed by combustion, 58

       Water, is it a good or bad conductor of heat, 151

       Water, why does it extinguish fire, 306

       Water, why, when a blacksmith thrusts a hot iron into a tank, do we perceive a peculiar smell, 309

       Water, why does it freeze, 324

       Water, why does it become steam, 326

       Water, how many degrees of latent heat are hidden in its several states, 327

       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

       LESSON LXXV.

       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, what is it, 748

       Water, why does it become solid when it freezes, 751

       Water, why does it boil, 753

       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 sometimes hard, 760

       Water, why is rain-water soft, 761

       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

       LESSON LXXVI.

       Water, what is the pressure of, 775

       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 does oil float upon it, 797

       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 it, 1199

       LESSON LXXVII.

       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

       Whirlwinds, what are they, 678

       Why do we see, 963

       Why do we wink, 975

       Why do we weep, 977

       Why do we hear, 983

       Why do we taste, 986

       Why do we smell, 992

       Why do we feel, 1004

       Why do we sleep, 1019

       Why do we dream, 1020

       Why do suppers produce dreaming, 1021

       Why do we yawn, 1022

       Why do we cough, 1023

       Why do we sneeze, 1024

       Why do we sigh, 1025

       Why do we laugh, 1026

       Why do we hiccough, 1027

       Why do we snore, 1028

       Why do we feel hungry, 1337

       Why do we feel thirsty, 1338

       Wick of a candle, why does it turn black as it burns, 225

       Wick