MineraUen,, 1873), both for further information on the subject generally, and for lists of the more important recent publications. How valuable it has become may be seen from the fact that these transparent sections, examined between two Nicol s prisms, from the phenomena of the interference of light, readily enable the observer to deter mine to which of the six systems of crystallization the mineral interposed belongs, and thus to fix one of its most essential characters. In this way the exact composition of many fine-grained crystalline rocks can be determined, and
much light thrown on their history.In regard to the other physical properties of crystals, it must suffice to say that they all indicate a similar close dependence on their geometric character. The same systems shown by their mathematical forms and optic properties reappear in reference to their relations to heat, magnetism, electricity, and other properties. The regular or tesseral minerals, with simple refraction of light, are shown by Senarmont s researches also to conduct heat uniformly in all directions, and their magnetic and electric peculiarities are similar. The tetragonal and hexagonal crystals with one chief axis, as they show double refraction of light with a single optic axis, have also analogous modes of conducting heat, of expanding under its influence, and of transmitting magnetism and electricity. And again, the three other systems with unequal axes, as they show two optic axes, exhibit also corresponding peculiarities in respect to the other properties mentioned. In this we have a remarkable instance of connection of the various physical sciences, and a strong proof of the sound basis that crystallography attained by the discoveries of Weiss and Mohs.
A great deal has been recently done in improving the instruments employed in determining the forms and dimensions of crystals. Though for first and rough approximations to the angles the early form of the hand goniometer may still be used, even the reflecting goniometer of Wollaston no longer meets the requirements of modern accuracy. In 1820 the Royal Academy of Sciences at Berlin offered a prize for the best methods of measuring these angles, which was gained by Dr Kupffer. Malus added a telescope to Wollaston s goniometer, and other methods of increasing its accuracy have been proposed, as by Babinet and Mitscherlich. Frankenheim, Haidinger, and others have also endeavoured to perfect the methods or means of observation which now, as tested by comparison with the results of calculation, seem fully adequate to the wants at least of determinative mineralogy.
The forms of crystals that occur in. native minerals are described more or less fully in several of the works already mentioned. The Atlas der Krystal-Formcn des Mineralreichcs of Dr A. Schrauf, 1865-1873, is intended to form a complete collection, of all the forms observed in the mineral kingdom, estimated as exceeding 10,000 in number, described in very many separate treatises and memoirs, and every day becoming more numerous. The arrange ment is alphabetical, and the work, from its accuracy and rich material, is highly valuable but still unfinished. The forms of salts and artificial crystals are described in Rammelsberg s Handbuch, der Tcrystallographische Chemie, 1855, and supplement, 1857, and many of them also in Groth s Kryslallographic.
The history of crystallography is related in C. M. Marx s Ocschichte der Krystallkiindc, 1825 ; Whewell s History of the In ductive Sciences, vol. iii. ; Von Kobell s Gcschichte der Afineralogie, 1864 ; Keungott s Uebersicht der Resultate der Mincraloqische For- schungen, 1844-1865 ; Quenstedt s Grttndriss, 1873, &c., from which further information may be obtained.
CSOKONAI, Mihaly Vitez (1773-1805), an Hungarian poet, was born at Debrecsin in 1773. Having been educated in his native town, he was appointed while still very young to the professorship of poetry there ; but soon after he was deprived of the post on account of the immor ality of his conduct. The remaining twelve years of his short life were passed in almost constant wretchedness, and lie died in his native town, and in his mother s house, when only thirty-one years of age. Csokonai was the author of a mock-heroic poem called Dorottya, two or three comedies or farces, and a number of love-poems. Most of his works have been published, with a life, by Schedel (1844-47).
CSOMA DE KÖRÖS, Alexander (c. 1790-1842), or as the name is written in Hungarian, Korosi Csoma Sandor, an Hungarian traveller and philologist, born about 1790 at Koros in Transylvania, belonged to a noble family which had sunk into poverty. He was educated at Nagy- Enyed and at Gottingen ; and, in order to carry out the dream of his youth and discover the origin of his country men, he divided his attention between medicine and the Oriental languages. In ] 820, having received from a friend the promise of an annuity of 100 florins (about 10) to support him during his travels, he set out for the East. He visited Egypt, and made his way to Tibet, where ho spent four years in a Buddhist monastery studying the language and the Buddhist literature. To his intense dis appointment he soon discovered that he could not thus obtain any assistance in his great object ; but, having visited Bengal, his knowledge of Tibetan obtained him employment in the library of the Asiatic Society there, which possessed more than 1000 volumes in that language; and he was afterwards supported by the Government while he published a Tibetan-English dictionary and grammar (both of which appeared at Calcutta in 1834). He also contributed several articles on the Tibetan language and literature to the Journal of the Asiatic Society of Bengal, and he published an analysis of the Kah-Gyur, the most important of the Buddhist sacred books. Meanwhile his fame had reached his native country, and procured him a pension from the Government, which, with characteristic devotion to learning, he devoted to the purchase of books for Indian libraries. He spent some time in Calcutta, -studying Sanskrit and several other languages ; but, early in 1842, he commenced his second attempt to discover the origin of the Hungarians. He had only reached Darjiling when he died on the llth April 1842. An oration was delivered in his honour before the Hungarian Academy by Eotros, the novelist.
CTESIAS, a Greek physician and historian, who flourished in the 5th century B.C. He was born of an Asclepiad family at Cnidus in Caria, and was in the early part of his life physician to Artaxerxes Mnemon, having, according to Diodorus Siculus, been taken prisoner of war. He was the author of a treatise on rivers, another on the Persian revenues, a history of India, which is only of value as recording the beliefs of the Persians about India, and, most famous of all, a history of Persia the Persica, written i:i opposition to Herodotus, and professing to be founded on (ho Persian royal archives. Of his two histories we possess abridgments by Photius, which have been published by Stephens (Paris, 1557-1594). As to the worth of the Persica there has been much controversy, both in ancient and modern times. Its chief modern de fenders have been Frcret, in the Memoires de V Academic des Inscriptions, vol. v., and Biihr, in his Prolegomenon to his edition of what has come down to us of the works of Ctesias (Frankfort, 1824). Aristotle rejected the testimony of Ctesias, which is opposed to that of the Jewish Scrip tures, of the Persian historian Berosus, and of recently discovered cuneiform inscriptions. See Rawlinson s Hero- dotiis (vol. i. pp. 71-74).
situated on the left bank of the Tigris, about twenty-five miles south-east of Baghdad. It is reported by Ammianus to have been founded by a Parthian, Varanes by name, of whose history nothing is known ; it rose into importance when the city of Seleucia on the opposite bank began to
decline; and under the Parthian kings, who originally