GYPSIES. 417 GYROSCOPE. (See Manures and Manuring.) It is also em- ployed at times to counteract the blacls alkali which forms in many of the soils of the arid region. Alabaster has been used for many years for decorative purposes, and in the making of statuary, while satin spar has been employed for necklaces, inlaid work, and other ornaments. The total quantity of gypsum produced in the United States in 1901 amounted to l,24ti,G49 short tons, valued at .'51„577.493, and of this quantity 521,292 short tons were calcined. In the United States Kansas is the largest producer, with ilichigan second. The imports in 1901 were valued at $326,670. Among the world'.s producers France leads, with the United States .second and Canada third. BiBLiooRAPiiT. Grimsley and Bailey, Gypsum. DeposilK of Kansas, issued by Kansas Geological Survey (Topeka, 1899) ; Wilkinson, "Technology of Cement Plaster," Transactions of the Ameri- can Institute of Mining Engineers (New York, 1897) ; La Croix, "Le gypse de Paris et les mine- rau.x qui I'accompagnent," Xouvclles arcltires des museum histoire naturellc (Paris, 1897). Tor statistics, consult volumes of the Mineral Re- sources, issued by the United Slates Geological Survey (^S"asllington, annual). See Plaster oi' Paris". GYPSY MOTH. This insect is abundant throughout the temperate zone in the Old World, and often does much damage to fruit, shade, and forest trees, particularly in France, Germany, and Southern Russia, It was first described by Linna'us in 1758, and named by him Bomhyx dispar, but later authorities place it in the genus Porthetria. The eggs of the moth are laid in August in a yellow, hairy mass on tree-trunks, rocks, and fences. They hatch the following spring, and the caterpillars feed on all kinds of trees, shrubs, and plants. Even conifers are not exempt from their ravages, and the latter trees usually die after one defoliation. B.y the middle of July the caterpillars become full grown, when they pupate in loose cocoons in sheltered places, and the moths emerge in about two weeks' time. The male moth is brown, and flies ac- tively, while the large white female does not fly. This insect was introduced into iledford. JIass., by Leopold Trouvelot, who in 1869 W'as experi- menting with various American and European silkworms in the efl'ort to find some hybrid which might be exempt from the attacks of the pebrine disease of silkworms. Trouvelot's specimens escaped accidentally, and although he notified the proper authorities, the matter was lo.st sight of until about 1889, when the ravages of the caterpillars at Medford were sufficient to cause general alarm. A j'car or two of desultory ef- forts on the part of property-owners in this vicinity were sufficient to convince them that they could not successfully cope with the insect, and the aid of the State was asked. In 1890 the Legislature of Jlassachusetts began the effort to exterminate the moth, first placing the work in the hands of a commission, and later trans- ferring it to the State Board of Agriculture. This work was carried on .systematically for about ten years, at an aggregate expense to the State of nearly .$1,000,000. when it was permitted to lapse, chiefly because public sentiment in Massachusetts would not support it further. The insect having become scarce, it was difficult to convince taxpayers of the necessity of further appropriations to secure the last remaining ones. Since the aliandoiuuent of the work by the Legis- lature in 1900, tlie moth has gradually increa'sed to a point where .several municipalities have been obliged to take up the work of destroying it, using the methods originated and perfected by the Board of Agriculture. Unless thorough work can be prosecuted over the entire district, it is quite probable that in a few years damage by the moth will become nuich more severe than ever before. Consult : Forbush and Fernald, "The Gypsy Moth," Massachusetts ^tale Hoard of Agriculture (Boston, 1890) ; Howard, "The Gypsy Jloth in America," Bulletin 11, United iSlntes Department of Agriculture (Washington, 1898). GYPSY MUSIC. See IUgtab Music. GYRATION, Centre of. See Centre of Gy- ration. GYRFALCON (OF. gerfaucon. girfaueun, ger- fault, Sp. gerifalte. gerifulco. from ML. hirrn- fnleo, gyrfalcon, from Gk. Jepis, hieros, sacred; popularly connected with Upa.^, hierax, falcon, although the words are only remotely akin, + Lat. faleo, falcon, confounded in popular ctyniol- ogj' with Lat. gyrus, circle, in fancied allusion to the bird's circling flight). A large falcon {Faleo rusticolus, or Faleo Islandicus), the fe- male of which is about two feet in entire lengtli. The plumage is almost brown when the bird is young, but gradually changes to white as it ad- vances in age, the white margin of each feather encroaching on its brown centre, until aged birds are almost pure white. It is rarely seen in the United States or other temperate regions, except in severe winters, but inhabits all the very cold northern parts of the world. It was formerly in high esteem for falconry, and was.^5rocured at gieat expense from Iceland and Norway. Two species and two subspecies are recognized in -America. Sec Plate of Falcons and Falconry. GY'ROMAN'CY. See Superstition. GYRON'NY. See Heraldry. GY'ROSCOPE ( from Gk. yOpos, gyros, circle + dKOTreiv, sl-opeiii. to view). The name given bv loucault to an instrument for the exhibition of various properties of rotation, and tlie composi- tion of rotations first described by Bohnenbcrger in 1817. It differs from a top in having both ends of its axis supported. The invention is probably French or German, and in some of its forms it dates from about the end of the eigh- teenth century, but no certain information can be obtained as to the original inventor. Its ac- tion is based on the principle that if a mass is set in rotation about its principal axis of inertia of greatest or least moment, it will continue to revolve about it, and unless extraneois f<u-ce is applied the direction of the axis will remain unchanged. If. then, a mass of metal — as, for instance, a circular disk, loaded at the rim and revolving in its owni plane — be made to rotate rapidly about its axis of greatest moment of in- ertia, and if it be freely supported (in gimbals, like the box of a compass), the direction of its axis will be the same so long as the rotation lasts. It will, therefore, constantly point to the same star, and may be employed to show that the apparent rotation of the stars aliout the earth is due to a real rotation of the earth itself in
