Electric lamps, vacuums in, 12*, 317; incandescent, 125; gas-filled, 317. Electric motors, 256*-257*. Electrolysis apparatus, 294-295*. Electromagnets, 247-257*. Electrons, 193; description of, 197; number of, in negative and in positive charges, 198-200. Elements, defined, 293; chemists' abbreviations of, 297-299; list of common, 299-300; hiding of, in compounds, 300-301. Emulsion, defined, 261; difference between solution and, 263. Energy released by chemical change, 340-341. Engine, working of cylinder and piston of, 344*. Ether, carrying of heat and light by, 124-125; light as waves of, 163-164. Ether waves, 124-125, 163-164. Evaporating dish, 101*. Evaporation, 100-106*; part taken by, in formation of clouds, rain, and dew, 277. Expansion, caused by heat, 88-93; cooling from, 94-96*. Expansion ball and ring experiment, 91*-92. Explosions, use of, 342* ff.; automobiles made to go by succession of, 344-345; cause of, 345; shooting of guns caused by, 345-346. Explosives, manufacture of, 347. Extension lights, 238. Eye, lens of, 142; section of, 151*; working of, 151*-153. Fading, process of, 326-327. Filament of incandescent lamp, 125. Fire engines, need of, to force water high, 9. Fire extinguishers, action of, 317. Fires, caused by electric arcs, 236; putting out of, by water, 317. _See_ Burning. Flames, formation of, 318. Floating, sinking and, 23-28. Focus of light, 142*-149*. Fogs, cause of, 288. Food, light necessary to production of, 332-333. Force, overcoming of extra motion by, in lever, 63-64*; reason for, of steam, 110. Forecasters, weather, 282-285. Form, elasticity of, 86-87. Freckles, cause of, 327. Freezing and melting, 96-99. Friction, 49-55*; electricity produced by, 197-198*. Frost, 97, 275; explanation of, 287. Fuel, chief elements in, 315-316. Fulcrum of lever, 59-60*. Fuse gap, the, 241*, 379*. Fuses, short circuits and, 240-245. Gas, cooling of, on expanding, 94-95; carbon and hydrogen in, 315; used for filling electric lamps, 317-318; will not burn until hot enough, 323-324; an explosion the sudden release of a confined, 348. Gases, diffusion of, 269-271; as elements, 293-294. Gas heaters, action of, 319, 321*, 322*. Gasoline, evaporation of, 103; boiling of, 112; distilled from petroleum, 114; elements of, 315; action of, in making automobiles go, 344-345. Geysers, cause of, 110. Glass, a poor conductor of heat, 118; used as insulator of electricity, 215. Glowworms, reason for glowing of, 341-342. Gold, an element, 293, 299; plating of, 339. Gravitation, defined, 3. Gravity, 1; pull of, opposed to pull of adhesion, 42-43. Grease, friction diminished by, 53-54; combined with lye to form soap, 357.