Jew's-harps, why will they not produce loud sounds unless they are applied to the mouth, 852 Jew's-harps, why does the alteration of the form of the mouth alter the sounds, 853 Kangaroos and opossums, why have they pouches in which they carry their young, 1139 LESSON XLIII. Kettle-holders, of what use are they, 128 Kettles and saucepans, why should the lids and fronts of be kept bright, 206 Kettles, why do they become encrusted with stony deposits, 762 Kite, why does it rise in the air, 840 Kite-string, why does it feel hot when running through the hand, 841 Kite, why does running with it cause it to ascend, 812 Knowledge, why should we seek it, 1 Knowledge, why does the possession of it give us power, 2 Knowledge, what are the benefits of, 3 Latent heat, will the abstraction of it reduce the bulk of bodies, 337 Latent heat, how do we know that it exists in air, 339 Laugh, why do we, 1026 Ligaments, what are they, 937 Ligaments, why are they wrapped around the joints, 938 Light, what is it, 451 Leaves, why are they green, 1181 Leaves, why do some turn yellow, 1186 Leaves, why do they fall off in the autumn, 1187 Leaves, how to make skeleton, 1159 LESSON XLIV. Leaves, why do they turn brown in autumn, 1183 Legs crossed, why do we see the elevated leg move at regular intervals, 918 Light, at what velocity does it travel, 453 Light, how long does it take to travel from the sun to the earth, 454 Light what are the minor sources of, 457 Light, what is a ray of, 458 Light, what is a medium of, 459 Light, what is a beam of, 460 Light, what is a pencil of, 461 Light, what is the radiant point, 462 Light, what is the focus of, 463 Light, what is the constitution of a ray of, 464 Light, why are its rays white, 465 Light, what are the estimated vibrations of, 465 Light, what is the refraction of, 472 Light, is it refracted when it falls upon a surface in a straight line, 473 Light, is the direction in which its rays are best dependent on the densities of the media, 474 Light, why does a spoon look bent when placed in a basin of water, 477 Light, why do we see the rays of the sun burst through the clouds in different directions, 478 LESSON XLV. Light, why is the apparent depth of water always deceptive, 479 Light, why are some substances opaque to it, 511 Light, how do we know that bodies reflect it in every direction, 517 Light, meditation on, 517 Light and heat, what are the differences between, 540 Light and heat, are they combined in the sun's rays, 541 Light and heat, how do we know that they are separate elements, 542 Light and heat, in what respects are they similar, 543 Light and heat, in what respects are they dissimilar, 544 Light, what is polarized, 549 Light, what is the velocity of artificial, 546