Flame of a candle, why does it terminate in a point, 250 Flame of a candle, why does it lengthen when anything is held over it, 251 Flame or spark, why does pressing it put it out, 253 Flame of a candle, why does holding a candle upside down put it out, 257 Flame of a candle, why is it more difficult to blow out the flame of a candle with a cotton wick than one with a rush wick, 258 Flame of a candle, why does blowing sharply on it put it out, 259 Flame of a candle, why will a gentle puff of air sometimes relight it, 260 LESSON XXXI. Flame of a candle, why will not a similar puff rekindle a rushlight, 261 Flame of a candle, why will a piece of paper twisted to form an extinguisher put it out, 263 Flame of a candle, why does it become dim when the wick is loaded with carbon, 267 Flames of a fire, why do some appear much whiter than others, 280 Flames of a fire, why do some of them appear blue, 282 Flesh, why does it heal when we cut it, 902 Flesh-eaters, why do they satisfy themselves with a rapid meal, 1092 Flesh, why do the marks of deep cuts remain, 905 Flesh, why does that under the nails look red, 907 Flies, how can they walk on the ceiling, 663 Flies, why have they fine hairs growing on the extremities of their legs, 1102 Flowers, what is the chief cause of the differences of their temperatures, 227 Flowers, why may wet weather be expected when their perfume is strong, 1103 LESSON XXXII. Flowers, why, if certain close, may rain be expected, 1116 Flying-top, why does it rise on the air, 843 Flying-top, why does it return to the earth, when its rotations are expended, 844 Focus, what is a, 81 Fogs, what are they, 365 Fogs, why are certain coasts very liable to them, 366 Fogs, what are dry, 367 Fogs, why do they frequently rise in the morning and fall in the evening, 371 Fogs, why do they sometimes rest upon a locality for days together, and then disappear, 372 Food, why do we eat it, 869 Food, why do we eat animal and vegetable, 172 Food, why do we masticate it, 871 Food, how does it descend into the stomach, 875 Food, why do we not feel it being transmitted through the throat, 876 Food, why do we feel uneasy after eating to excess, 877 Food, why do we feel drowsy after eating heartily, 878 Food, why do some portions nourish us, while other portions are useless, 883 LESSON XXXIII. Fossil, vegetable, what is it, 272 Friction, why does it produce heat, 321 Friction, why does rubbing two surfaces together attract latent heat, 322 Frost, why is the air warmer during, 163 Frost, what is white, 412 Frost, what is black, 413 Frost, why are black frosts said to last, 414 Fruit, why do gooseberries, plums, &c., taste acid, 1184 Fruit, why do ripe taste sweet, and unripe sour, 1185 Fruits, why are succulent most abundant in tropical climates, 1207