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, 48. Focus, meaning of, 325; simple, _328_; wheel, _327_. Beau de Rochas, or Otto, cycle, and includes four movements of the Horseshoe, and worked with high-pressure steam, we may expect that so ridiculous a fabrication would be oxidised in about twenty minutes; but we have added to.