Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/37

Rh Malay Islands by cognate forms. They are all frugivorous, and, being easily tamed and learning to pronounce words very distinctly, are favourite cage-birds. 1 In the New World the name Grackle has been applied to several species of the genera Scolccopkagus and Quiscalus, though these are more commonly called in the United States and Canada &quot; Blackbirds,&quot; and some of them &quot; Boat-tails.&quot; They all belong to the family Icteridce. The best known of these are the Rusty Grackle, S. ferruginous, which pervades almost the whole of North America, and Q. purpureus, the Purple Grackle or Crow-Blackbird, of more limited range, for though abundant enough in most parts to the east of the Rocky Mountains, it seems not to appear on the Pacific side. There is also Brewer s or the Blue-headed Grackle, S. cyanocephaltis, which has a more western range, not oc curring to the eastward of Kansas and Minnesota. A fourth species, Q. major, is also found to inhabit the Atlantic States as far as Nor tli Carolina. All these birds are of exceedingly omnivorous habit, and though undoubtedly destroying large numbers of pernicious insects are in many places held in bad repute from the mischief they do to the corn crops.  GRACIAN, (1584-1653), one of the princi pal &quot; cultistas &quot; or Spanish prose writers of the school of Gongora, was born at Calatayud, Aragon, in 1584. Little is known of his personal history except that on attaining to manhood he entered the Society of Jesus, and that ulti mately he became rector of the Jesuit College at Tarragona, where he died in 1658. His principal works are El lleroe (1630), written in short compact sentences, which has been described as a sort of recipe for miking a hero ; La Agudeza, y A tie de Ingenio (16 48), a sort of art of poetry or system of rhetoric in which the principles of &quot;Gongorism&quot; are inculcate! ; Or it icon (1650-53), an allegory in which, under the imigery of the seasons of the year, the course of human life is described; El Discreto, a delineation of the typical character of a courtier j Oraculo Manual, a system of rules for the conduct of life. His works, which have been often reprinted in Spanish under the name of his brother Lorenzo, have also for the most part been translated into French and Italian. The Oraculo Manual has been translated into German by A. Schopenhauer (1862), and into English anonymously (Courtier s Manual Oracle, 1684). The Hero also occurs in English (from the French, 1726). Gracian s merits as a writer have been very differently estimated by his critics, and it is probable that from none of them has he received strict justice. If his style is hardly so bombastic, involved, and obscure as his enemies represent it, neither can he in fairness receive all that credit for depth and originality of thought which is claimed for him by his friends. As examples of the widely differing appreciations which have been passed upon him, see Ticknor s Spanish Literature, vol. iii., and Mr Grant Duff s Miscellanies (1878).  GRADISCA, a town of Austria, in the principality of Gorz and Gradisca, situated about 10 miles S.W. of Gorz, on the right bank of the Isonzo. It was formerly a strongly fortified place, but its citadel is now occupied as a prison. The inhabitants of the commune, who numbered in 1869 rather more than 3000, are engaged in silk spinning. Be tween 1471 and 1481 Gradisca was fortified by the Venetians, but in 1511 they surrendered it to the imperial forces. ^ In 1647 Gradisca and its territory, including Aquileia and forty-three smaller places, was erected into a prince-countship in favour of the prince of Eggenberg. It lapsed in 1717 to the imperial crown, and in 1754 was completely incorporated with Gorz. The name was revived by the constitution of 1861, which established the crown- land of the countship of Gorz and Gradisca. See GORZ. 1 For a valuable monograph on the various species of Gracula and its allies see Prof. Schlegel s Bijdrage tot de Kennis van het Gcsch- lacht Beo (Nederlandsch Tydschri/t voor de Dierkunde, i. pp. 1 -9).  GRADUATION is the name given to the art of dividing straight scales, circular arcs, or whole circumferences into any required number of equal parts. It is the most im portant and difficult part of the work of the mathematical instrument maker, and is required in the construction of most physical, astronomical, nautical, and surveying instru ments, such as thermometer scales, linear measuring instru ments, quadrants, sextants, mural circles, theodolites, &c. The art was, undoubtedly, first practised by clockmakers for cutting the teeth of their wheels at regular intervals ; but so long as it was confined to them, no particular delicacy or accurate nicety in its performance was required. This only arose when astronomy began to be seriously studied, and the exact position of the heavenly bodies to be deter mined, which created the necessity for strictly accurate means of measuring linear and angular magnitude. Then graduation began to be looked upon as an art which required special talents and training, and hence we find that all the best artists have spent their best efforts on the perfecting of astronomical instruments. Of these may be named Abraham Sharp, Bird, Smeaton, Ramsden, the Due de C haulnes, John and Edward Troughton, Simms, and Ross. It is obvious that the first graduated instrument must have been done by the hand and eye alone, whether it was in the form of a straight-edge with equal divisions, or a screw, or a divided plate ; but, once in the possession of one such divided instrument, it was a comparatively easy matter to employ it as a standard, and copy its divisions on any other article that might be desired. Hence graduation naturally divides itself into two distinct branches, original graduation and copying, which latter may be done either by the hand or by a machine called a dividing engine. We may thus speak of graduation under the three heads of original graduation, copying, and machine graduation

Original Graduation.&mdash;This is by far the most difficult part of the art so difficult, indeed, and requiring such accuracy of hand and eye, that but few in any generation have been completely competent for the task. The earlier astronomers graduated their own instruments, and, from the examples that have come down to us, it must have been very roughly done as compared with modern work. in regard to the graduation of straight scales, we have, by elementary geometry, the means, theoretically, of divid ing a straight line into any number of equal parts ; but the practical carrying out of the geometrical construction is so beset with difficulties as to render the method untrustworthy. This method, which employs the common diagonal scale, was used in dividing a quadrant of 3 feet radius, which belonged to Napier of Merchiston, and which only read to minutes a result, say Thomson and Tait (Nat. 7Yu7.), &quot; giving no greater accuracy than is now attainable by the pocket sextants of Troughton and Simms, the radius of whose arc is little more than an inch.&quot; The original graduation of a straight line is, in practice, clone either by the method of continual bisection or by stepping. In continual bisection the entire length of the line is first laid down. Then, as nearly as possible, half that distance is taken in the beam-cotnpass and marked off by faint arcs from each end of the line. Should these marks coincide the exact middle point of the line is obtained. If not, as will almost always be the case, the distance between the marks is carefully bisected by hand with the aid of a magnifying gbss. The same process is again applied to the halves thus obtained, and so on in succession, dividing the line into parts represented by 2, 4, 8, 16, I.Y.C., till the desired divisions are reached. In the method of stepping the smallest division required is first taken, as accurately as possible, by spring dividers, and that distance is then laid off, by successive steps, from one end of the line. It is evident that, in this method, any error at starting will be

