remains fixed. The crystal is placed on the holder and adjusted
so that the edge (zone-axis) between two faces is coincident with the
axis of the instrument. Light from an incandescent gas-burner
passes through the slit of the collimator C, and the image of the slit
(signal) reflected from the crystal face is viewed in the telescope.
The clamp α and slow-motion screw F enable the image to be
brought exactly on the cross-wires of the telescope, and the position
of the circle with respect to the vernier is read through the lens.
The crystal and the circle are then rotated together until the image
from a second face is brought on the cross-wires of the telescope, and
the angle through which they have been turned is the angle between
the normals to the two faces. While measuring the angles between
the faces of crystals the telescope remains fixed by the clamp β, but
when this is released the instrument may be used as a spectrometer
or refractometer for determining, by the method of minimum
deviation, the indices of refraction of an artificially cut prism or of a
transparent crystal when the faces are suitably inclined to one
another.
With a one-circle goniometer, such as is described above, it is necessary to mount and re-adjust the crystal afresh for the measurement of each zone of faces (i.e. each set of faces intersecting in parallel edges); with very small crystals this operation takes a considerable time, and the minute faces are not readily identified again. Further, in certain cases, it is not possible to measure the angles between zones, nor to determine the position of small faces which do not lie in prominent zones on the crystal. These difficulties have been overcome by the use of a two-circle goniometer or theodolite-goniometer, which as a combination of a vertical-circle goniometer and one with a horizontal-circle was first employed by W. H. Miller in 1874. Special forms have been designed by E. S. Fedorov (1889), V. Goldschmidt (1893), S. Czapski (1893) and F. Stoeber (1898), which differ mainly in the arrangement of the optical parts. In these instruments the crystal is set up and adjusted once for all, with the axis of a prominent zone parallel to the axis of either the horizontal or the vertical circle. As a rule, only in this zone can the angles between the faces be measured directly; the positions of all the other faces, which need be observed only once, are fixed by the simultaneous readings of the two circles. These readings, corresponding to the polar distance and azimuth, or latitude and longitude readings of astronomical telescopes, must be plotted on a projection before the symmetry of the crystal is apparent; and laborious calculations are necessary in order to determine the indices of the faces and the angles between them, and the other constants of the crystal, or to test whether any three faces are accurately in a zone.
These disadvantages are overcome by adding still another graduated circle to the instrument, with its axis perpendicular to the axis of the vertical circle, thus forming a three-circle goniometer. With such an instrument measurements may be made in any zone or between any two faces without re-adjusting the crystal; further the troublesome calculations are avoided, and, indeed, the instrument may be used for solving spherical triangles. Different forms of three-circle goniometers have been designed by G. F. H. Smith (1899 and 1904), E. S. Fedorov (1900) and J. F. C. Klein (1900). Besides being used as a one-, two-, or three-circle goniometer for the measurement of the interfacial angles of crystals, and as a refractometer for determining refractive indices by the prismatic method or by total reflection, Klein’s instrument, which is called a polymeter, is fitted with accessory optical apparatus which enables it to be used for examining a crystal in parallel or convergent polarized light and for measuring the optic axial angle.
Goniometers of special construction have been devised for certain purposes; for instance, the inverted horizontal-circle goniometer of H. A. Miers (1903) for measuring crystals during their growth in the mother-liquid. A. E. Tutton (1894) has combined a goniometer with lapidaries’ appliances for cutting section-plates and prisms from crystals accurately in any desired direction. The instrument commonly employed for measuring the optic axial angle of biaxial crystals is really a combination of a goniometer with a polariscope. For the optical investigation of minute crystals under the microscope, various forms of stage-goniometer with one, two or three graduated circles have been constructed. An ordinary microscope fitted with cross-wires and a rotating graduated stage serves the purpose of a goniometer for measuring the plane angles of a crystal face or section, being the same in principle as the contact goniometer.
For fuller descriptions of goniometers reference may be made to the text-books of Crystallography and Mineralogy, especially to P. H. Groth, Physikalische Krystallographie (4th ed., Leipzig, 1905). See also C. Leiss, Die optischen Instrumente der Firma R. Fuess, deren Beschreibung, Justierung und Anwendung (Leipzig, 1899). (L. J. S.)
GONTAUT, MARIE JOSÉPHINE LOUISE, Duchesse de
(1773–1857), was born in Paris on the 3rd of August 1773,
daughter of Augustin François, comte de Montaut-Navailles,
who had been governor of Louis XVI. and his two brothers when
children. The count of Provence (afterwards Louis XVIII.)
and his wife stood sponsors to Joséphine de Montaut, and she
shared the lessons given by Madame de Genlis to the Orleans
family, with whom her mother broke off relations after the
outbreak
of the Revolution. Mother and daughter emigrated to
Coblenz in 1792; thence they went to Rotterdam, and finally
to England, where Joséphine married the marquis Charles
Michel de Gontaut-Saint-Blacard. They returned to France
at the Restoration, and resumed their place at court. Madame
de Gontaut became lady-in-waiting to Caroline, duchess of
Berry, and, on the birth of the princess Louise (Mlle d’Artois,
afterwards duchess of Parma), governess to the children of
France. Next year the birth of Henry, duke of Bordeaux
(afterwards known as the comte de Chambord), added to her
charge the heir of the Bourbons. She remained faithful to his
cause all her life. Her husband died in 1822, and in 1827 she
was created duchesse de Gontaut. She followed the exiled royal
family in 1830 to Holyrood Palace, and then to Prague, but in
1834, owing to differences with Pierre Louis, duc de Blacas, who
thought her comparatively liberal views dangerous for the
prince and princess, she received a brusque congé from Charles X.
Her twin daughters, Joséphine (1796–1844) and Charlotte (1796–1818),
married respectively Ferdinand de Chabot, prince de Léon
and afterwards duc de Rohan, and François, comte de Bourbon-Busset.
She herself wrote in her old age some naïve memoirs,
which throw an odd light on the pretensions of the “governess
of the children of France.” She died in Paris in 1857.
See her Memoirs (Eng. ed., 2 vols., 1894), and Lettres inédites (1895).
GONVILE, EDMUND (d. 1351), founder of Gonville Hall, now Gonville and Caius College, at Cambridge, England, is thought to have been the son of William de Gonvile, and the brother of Sir Nicholas Gonvile. In 1320 he was rector of Thelnetham, Suffolk, and steward there for William, earl Warren and the earl of Lancaster. Six years later he was rector of Rushworth, and in 1342 rector of Terrington St John and commissioner for the marshlands of Norfolk. In this year he founded and endowed a collegiate church at Rushworth, suppressed in 1541. The foundation of Gonville Hall at Cambridge was effected by a charter granted by Edward III. in 1348. It was called, officially, the Hall of the Annunciation of the Blessed Virgin, but was usually known as Gunnell or Gonville Hall. Its original site was in Free-school Lane, where Corpus Christi College now stands. Gonvile apparently wished it to be devoted to training for theological study, but after his death the foundation was completed by William Bateman, bishop of Norwich and founder of Trinity Hall, on a different site and with considerably altered statutes. (See also Caius, John.)
GONZAGA, an Italian princely family named after the town where it probably had its origin. Its known history begins with the 13th century, when Luigi I. (1267–1360), after fierce struggles supplanted his brother-in-law Rinaldo (nicknamed Passerino) Bonacolsi as lord of Mantua in August 1328, with the title of captain-general, and afterwards of vicar-general of the empire, adding the designation of count of Mirandola and Concordia, which fief the Gonzagas held from 1328 to 1354. In July 1335 his son Guido, with the help of Filippino and Feltrino Gonzaga, wrested Reggio from the Scaligeri and held it until 1371. Luigi was succeeded by Guido (d. 1369); the latter’s son Luigi II. came next in succession (d. 1382), and then Giovan Francesco I. (d. 1407), who, although at one time allied with the treacherous Gian Galeazzo Visconti, incurred the latter’s enmity and all but lost his estates and his life in consequence; eventually he joined the Florentines and Bolognese, enemies of Visconti. He promoted commerce and wisely developed the prosperity of his dominions. His son Giovan Francesco II. (d. 1444) succeeded him under the regency of his uncle Carlo Malatesta and the protection of the Venetians. He became a famous general, and was rewarded for his services to the emperor Sigismund with the title of marquess of Mantua for himself and his descendants (1432), an investiture which legitimatized the usurpations of the house of Gonzaga. His son Luigi III. “il Turco” (d. 1478) likewise became a celebrated soldier, and was also a learned and liberal prince, a patron of literature and the arts. His son Federigo I. (d. 1484) followed in his father’s footsteps, and served under various foreign sovereigns, including Bona of Savoy and Lorenzo de’ Medici; subsequently he upheld the rights of the house of
