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LEFT FLUXION 161 FLYING BUTTRESS six. By means of these they are able to execute any music, howevez* chromatic, if within theii- compass, which extends from C below the treble to C in altissimo. In December, 1832, a flute of an entirely new construction was invented by Mr. Boehm, of Munich. It, however, remained in obscurity until 1837, when it was adopted and inti'oduced to the French professors by Mr. Cadmus; but they con- sidered its adoption would be attended with too much trouble, in consequence of its having an open G-sharp key. This, hov.'ever, was soon afterward remedied by Mr. Dorus, who put a shut G-sharp key in its place. It now became univer- sally adopted. In architecture, an upright channel on the shaft of a column, usually ending hemispherically at the top and bottom. Their plane or horizontal section is some- times semicircular, or segmental, or ellip- tical, as in some examples of Grecian architecture. The Doric column has 20 flutes round its circumference; the Ionic, Corinthian, and Composite have respec- tively 24. FLUXION, in medicine, an unnatural flow or determination of blood or other humor toward any organ; a catarrh. In mathematics, a method of calcula- tion resulting from the operation of fluents, or flowing numbers. FLY, in zoology, a name applied al- most indiscriminately to all insects possessing wings; being often extended to all insects of the sub-order Diptera, and often also restricted to the family MuscicUe. The fly is characterized as pos- sessing a pair of veined and membranous wings, with two movable bodies called balancers (halteres), placed a little be- hind them. The mouth is formed of be- tween two and six setaceous pieces of scaly texture, and these pieces are either inclosed in a proboscis-like sheath, or covered by one or two laminae, which form it. The head is globular or hemi- spherical. The mouth is only formed for transmitting fluids, and is conse- quently very delicate in structure. The sucker performs the part of a lancet, and pierces the envelope of vegetable or ani- mal fluids, in order to allow of the fluid itself being transmitted up into the mouth of the insect. The antennae are united in front, and are approximated at the base. Above the true wings of the insect and a little behind them, ai'e the balancers or halteres; these are almost rnembranous, and are furnished with two little knobs at their extremities, which are capable of dilatation. The legs of this class of insects are long and slender; and the feet, it is well known, are fui-- nished with skinny palms, to enable them to stick on glass and other smooth bodies by means of the pressure of the atmos- phere. In machinery, that part of a machine which, being put in motion, regulates the rest. In nautical language that part of a compass on which the 32 points are drawn, and to which the needle is at- tached underneath; the compass-card. In printing, that part of the machinery of a printing press which withdraws the sheet, and lays it aside after the impres- sion is made. FLY CATCHERS, the Musicapidxa, an extensive family of birds, order Inses- sores, represented in North America by about 80 species. As their name implies, the fly catchers prey on insects, which they seize in mid-air. They have the beak horizontally depressed, and armed with bristles at its base, with the point more or less decurved and emarginated. The value of the insectivorous family of birds to man is incalculable. One of the best types of fly catchers is that pre- sented by the tyrant fly catcher, king bird or bee martin, Muscicapa Tyrannus, or Tyrannus Carolinensis. This bird is peculiar to America E. of the Rocky Mountains. It is 8 inches in length, and 14 in extent of wing. The general color of the upper parts is a dark bluish-gray, inclining to dull slate-black, on the head of which the central feathers along the crown form a gorgeous orange patch. The European species, Muscicapa grisola, the beam bird or bee bird, is distin- guished from any other by having much more slender bills, with shorter bristles at the gape. FLYING SQUIRREL FLYING BUTTRESS, in architecture, a structure in the form of an arch, span- ning the roof of an aisle between an outer buttress and the wall of the nave. It assists in resisting the thrust of the roof.