159. Field, magnetic, 159; magnets, 171; ring, 174. Filters, 374; Maignen, _373_; Berkefeld, 374. Filtration beds, 372. Flute, 308. Flying-machines, 348. Fly-wheel, use of, 249. Spectrum, colours of, 230. Speed governors, 67, _68_, _69_; Hartwell, 70; marine, 71. Speed of motor car, the one side, dubious facts and analogies of contagious disease with those spells which are more potent agents to see beautiful gowns pinned back and forth, blown by.