Undulation. A wave. Undulatory theory. The mechanical principles of the motion of waves. Vapour. Steam. Variation. A periodic inequality in the motion of the moon. Variation of the compass. The deviation of the compass needle from the true north. Vertical. The direction of the plumb-line. Vertical plane. A plane passing through the plumbline, consequently at right angles to the horizon. Vesicles. Small hollow spheres of water. Vibration. A motion to and fro. Visual ray. A ray of light coming from any object to the eye. Volta-electric induction. The disposition of elec tric currents to produce similar currents in bodies near them capable of receiving them. INDEX. ABERRATION of light, 31 Acceleration of the moon, Action, compound and dis- Algol, the star, 388 Alps, the, 273 Amazons, river of the, 117 Andes, the, 134 Arabian science, 108 Arago, M., 135, 219, 266, 341 Astronomical tables, 68 and repulsion, elec- trical, 291, 354 capillary, 123, 125 Eras and chronology, 100, Ether, all-pervading, 359 Ethereal medium, the, 192, Existence, grades of, 234 Faraday, Mr., 325, 336, 340, Figure of the earth, 48, 54, Fire, production of, 241 Forests, influence of, 264 Frost, hoar, 240 Galvanism, 300 et seq. 345 Glass, musical vibrations of, Sir John, 147, 195, 386, 391, 398 Isothermal lines, the, 267, Italy, the north of, 56 Jupiter, the revolution of, Kater, Captain, 106 La Grange on Periodical Language, its vocal articula- La Place, 22, 37, 73, 101, Laroche's experiments in its velocity calcu- lated, 412 Lightning, 297, 304 Magnet, the, 309-339 Magnetic pole, the, 310 Magnetism, theory of, 309, Malus, M., optical disco- Man, frame of, 251; species Marine plants, 279 its molecular action on light, 215 of Meridian, terrestrial, 54 Metals, dilation of, 243, 300 Moon, the, 34; distance of, 62 -, new, 45 luminous spots of and earth, reciprocal Muscular strength, 134 Nature, the laws of, 408, Nautical Almanac, 47 Navigation, new astrono- Nebulæ; clusters of stars, Needle, the magnetic, 310 Occultation of stars, 46 |