Clouds, what do Cirro-cumulus foretell, 393 Clouds, what do Cirro-stratus foretell, 394 Clouds, what do Cumulo-stratus foretell, 395 LESSON XVIII. Clouds, why are cloudy days colder than sunny days, 396 Clouds, why are cloudy nights warmer than clear nights, 397 Cloudy days and nights, why are they not always wet, 432 Clouds, why are they white, 531 Clouds, why are they sometimes yellow, 533 Clouds, what develops the electricity in the, 581 Clouds, why do they sometimes move towards each other from opposite directions, 778 Clouds, why do they gather around mountain tops, 781 Cloves, where are they produced, 1231 Coal, what is it, 271 Coal, why do we know that it is of vegetable origin, 273 Coal, what are the chemical components of, 274 Coals, why do they produce yellow flame, 279 Cockles, why have they stiff muscular tongues, 1087 Cocoa, what is it, 1195 Cocoa, what tree produces it, 1221 Coffee-pot, why has it a wooden handle, 125 LESSON XIX. Coffee, what is it, 1193 Coffee, where is it cultivated, 1224 Cohesion, what is the attraction of, 776 Coke-fires, why do they not give flames, 107 Coke, what is it, 278 Cold, when is a body said to be, 78 Cold, what is the cause of the sensation, 133 Cold, does it radiate, 207 Colour, why is a substance white, 466 Colour, why is a substance black, 467 Colour, why is a rose red, 468 Colour, why is a lily white, 469 Colour, why is a primrose yellow, 470 Colour, why are there so many varieties of colour and tint in nature, 471 Colours, remarks upon, 501 Combustion, what takes place during, 48 Combustion, how many kinds are there, 93 Conductors of heat, what substances are good, 110 Conductors of heat, why do bad conductors readily ignite, 295 Combustion, what is spontaneous, 311 Combustibles used for lighting, which vitiates the air most, 62 Conduction of heat, what is the, 113 Convection, what is the chief effect of the law of, 243 LESSON XX. Cork, what is it, 1271 Cork-tree, why does it shed its own bark, 1272 Corns, why when they ache may rain be expected, 1115 Corn, why does the young ear come up enfolded in two leaves, 1167 Cotton, what is it, 1199 Cough, why do we, 1023 Crickets, why do they make a chirping noise, 1123 Cross-bills, why do their mandibles overlap each other, 1136 Cup in a pie, why does it become filled with juice, 631 Cup in a pie, does it prevent the juice from boiling over, 662 Dates, what are they produced by, 1221 Death-watch, why does it make a ticking noise, 1301 Dew, what is it, 345 Dew, what causes the decline of temperature which produces it, 347 Dew, why is there little or none, when the nights are cloudy, 348 Dew, why does it form most abundantly on cloudless nights, 349 Dew, why is there little under the branches of thick foliage, 351 LESSON XXI.