COMMITTEE Chairman-The Right Hon. LOND BROUGHAM, F.R.S., Meinder of the National Institute of France. W. Allen, Esq., F.R. and R.A.S. Captain Beaufort, R.N., F. R. and R.A.S., Hydrographer to the Admiralty. G. Burrows, M.D. Peter Stafford Carey, Esq., A.M. William Coulson, Esq. R. D. Craig, Esq. J. F. Davis, Esq., F.R.S. H. T. Dela Beche, Esq., F.R.S. The Right Hon. Lord Denman, Samuel Duckworth, Esq. B. F. Duppa, Esq. The Right Rev. the Bishop of Durham, D.D. The Right Hon. Viscount Ebrington, M.P. Sir Henry Ellis, Prin. Lib. Brit. Mus. T. F. Ellis, Esq., A.M., F.R.A.S. John Elliotson, M.D., F.R.S. Thomas Falconer, Esq. I. L. Goldsmid, Esq., F.R. and R.A.S. Vice-Chairman-JOHN WOOD, Esq. Treasurer-WILLIAM TOOKE, Esq., F.R.S. B. Gompertz, Esq., F.R. and R.A.S. Rowland Hill, Esq., F.R.A.S. Right Hon. Sir J. C. Hobhouse, Bart., M.P. David Jardine, Esq., A.M. Henry B. Ker, Esq. Thomas Hewitt Key, Esq., A.M. J. T. Leader, Esq., M.P. George C. Lewis, Esq., A.M. 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Malkin. James Young, Esq. C. H. Cameron, Esq. Cambridge-Rev. James Bowstead, M.A. Rev. Prof. Henslow, M.A., F.L.S. & G.S. Rev. Leonard Jenyns, M.A., F.L.S. Rev. John Lodge, M.A. Rev. Geo. Peacock, M.A., F.R.S. & G.S. Rev. Prof. Sedgwick, M.A., F.R.S.& G.S. Canterbury-John Brent, Esq., Alderman. Canton.-Wm. Jardine, Esq., President. Robert Inglis, Esq., Treasurer. Rev. C. Bridgman, Rev. C. Gutzlaff, J. R. Morrison, Esq.,. Secretaries. Cardigan-Rev. J. Blackwell, M.A. Carlisle-Thomas Barnes, M.D., F.R.S.E. Carnarvon-R. A. Poole, Esq. William Roberts, Esq. Chester-Hayes Lyon, Esq. Henry Potts, Esq. Chichester-John Forbes, M.D., F.R,S. Cockermouth-Rev. J. Whitridge. Mr. Plato Petrides Coventry-Arthur Gregory, Esq. Denbigh-John Madocks, Esq. Thomas Evans, Esq. Lt. Col. C. Hamilton Smith, F.R.S. Dublin-T. Drummond, Esq. R.E., F.R.A.S. Edinburgh-Sir C. Bell, F.R.S.L. and E. Etruria-Jos. Wedgwood, Esq. Exeter-J. Tyrrell, Esq. John Milford, Esq. (Coaver.) Glamorganshire- Dr. Malkin, Cowbridge. W. Williams, Esq., Aberpergwm. Glasgow-K. Finlay, Esq. Professor Myine. Alexander McGrigor, Esq. Guernsey-F. C. Lukis, Esq. Keighley, Yorkshire-Rev. T. Dury, M.A. Lewes J. W. Woollgar, Esq. Ludlow-T. A. Knight, Esq., P.H.S. John Case, Esq. Malmesbury-B. C. Thomas, Esq. Manchester Loc. As.-G. W. Wood, Esq., Ch. Benjamin Heywood. Esq., Treasurer. Masham-Rev. George Waddington, M.A. T. Sopwith, Esq., F.G.S. Newport, Isle of Wight-Ab. Clarke, Esq. T. Cooke, Jur., Esq. R. G. Kirkpatrick, Erq. Newport Pagnell--J. Miller, Esq. Newtown, Montgomeryshire-W. Pugh, Esq. Norwich-Richard Bacon, Esq. Orsett, Essex-Dr. Corbett, M.D. Oxford-Dr. Daubeny, F.R.S. Frof. ofChem. Rev. John Jordan, B.A. Pesth, Hungary-Count Szechenyi. Plymouth-H. Woollcombe, Esq., F.A.S., Ch. E. Moore, M.D., F.L.S., Secretary. Presteign-Dr. A. W. Davies, M.D. Ripon Rev. H. P. Hamilton, M.A., F.R.S. and G.S. Rev. P. Ewart, M.A. Ruthen-Rev. the Warden of Humphreys Jones, Esq. Ryde, I. of Wight-Sir Rd. Simeon, Bt. Sheffield-J. H. Abrahams, Esq. Shepton Mallet-G. F. Burroughs, Esq. Shrewsbury-R. A. Slaney, Esq., M.P. South Petherton-John Nicholetts, Esq. St. Asaph-Rev. George Strong. Stockport-H. Marsiaud, Esq., Treasurer. Henry Coppock, Esq., Secretary. Sydney, New South Wales William M. Manning, Esq. Tavistock-Rev. W. Evans. John Rundle, Esq. Truro-Richard Taunton, M.D., F.R.S Henry Sewell Stokes, Esq. Tunbridge Wells-Dr. Yeats, M.D. Uttoxeter-Robert Blurton, Esq. Warwick-Dr. Conolly. The Rev. William Field, (Leamington.) Waterford-Sir John Newport, Bt. Wolverhampton-J. Pearson, Esq. Worcester-Dr. Hastings, M.D. C. H. Hebb, Esq. Wrexham-Thomas Edgworth, Esq. J. E. Bowman, Esq., F.L.S., Treasurer Dawson Turner, Esq. THOMAS COATES, Esq., Secretary, No. 59, Lincoln's Inn Fields. London: Printed by W. CLOWES ad SONS, Stamford-street, AUG 1 0 1921 Mrs. A. E. Proud fit. 9-10 THE PENNY CYCLOPÆDIA OF THE SOCIETY FOR THE DIFFUSION OF USEFUL KNOWLEDGE. DIO DIONY'SIUS THE YOUNGER, son of Dionysius the Elder, succeeded him as tyrant of Syracuse, being acknowledged as such by the people. His father had left the state in a prosperous condition; but young Dionysius had neither his abilities nor his prudence and experience. He followed at first the advice of Dion, who, although a republican in principle, had remained faithful to his father, and who now endeavoured to direct the inexperienced son for the good of his country. For this purpose Dion invited his friend Plato to Syracuse about 364 B.C. Dionysius received the philosopher with great respect, and in deference to his advice reformed for awhile his loose habits and the manners of his court. But a faction, led by Philistus, who had always been a supporter of the tyranny of the elder Dionysius, succeeded in prejudicing his son against both Dion and Plato. Dion was exiled under pretence that he had written privately to the senate of Carthage for the purpose f concluding a peace. Plato urgently demanded of Dioysius the recall of Dion, and not being able to obtain it, e left Syracuse, after which Dionysius gave himself up to Zebauchery without restraint. Aristippus, who was then at his court, was the kind of philosopher best suited to the Laste of Dionysius. Dion meantime was travelling through Greece, where his character gained him numerous friends. Dionysius, moved by jealousy, confiscated his property, and obliged his wife to marry another. Upon this Dion colected a small force at Zacynthus, with which he sailed for Sicily, and entered Syracuse without resistance. Dionysius retired to the citadel in the Ortygia, and after some resistance, in which old Philistus, his best supporter, was taken prisoner and put to death, he quitted Syracuse by sea, and retired to Locri, the country of his mother, where he had connexions and friends. His partisans, however, retained possession of Ortygia, and a faction having risen in the town, headed by Heraclides, a demagogue, who proposed an equal distribution of property, which Dion resisted, the latter was deprived of his command, and would have been killed by the excited populace, had not his soldiers escorted him safely to Leontini. In the midst of the confusion, a successful sortie made by the soldiers of Dionysius, who plundered and burnt part of the city, recalled the Syracusans to their senses, and messengers were dispatched after Dion, requesting him to return. Dion obeyed the call, repulsed the enemy, and soon after took the citadel. But the faction of Heraclides conspired against Dion, and had him treacherously murdered, 354 B.C. DIO of Dion. The latter sent messengers to Corinth to request assistance against Dionysius. The Corinthians appointed as leader of the expedition Timoleon, who had already figured in the affairs of his own country as a determined opponent of tyranny. Timoleon landed in Sicily 344 B.C., notwithstanding the opposition of the Carthaginians and o Iketas, who acted a perfidious part on this occasion; he entered Syracuse, and soon after obliged Dionysius to surrender. Dionysius was sent to Corinth, where he spent the remainder of his life in the company of actors and low women; some say that at one time he kept a school. Justin (xxi. 5) says that he purposely affected low habits in order to disarm revenge, and that being despised, he might no longer be feared or hated for his former tyranny. Several repartees are related of him in answer to those who taunted him upon his altered fortunes which are not destitute of wit or wisdom. (Plutarch, Dion.; Diodorus, xvi.) DIONY'SIUS, the son of Alexander, an historian and critic, born at Halicarnassus in the first century B. C. We know nothing of his history beyond what he has told us of himself. He states (Antiq., p. 20-24) that he came to Italy at the termination of the civil war between Augustus and Antony (B. c. 29), and that he spent the following two-andtwenty years at Rome in learning the Latin language and in collecting materials for his history. (Phot. Biblioth., cod. lxxxvi.) He also says (Antiq., p. 1725) that he lived in the time of the great civil war. The principal work of Dionysius is his Roman Antiquities, which commenced with the early history of the people of Italy, and terminated with the beginning of the first Punic war, B.C. 265. (Antiq. i. p. 22.) It originally consisted of twenty books, of which the first ten remain entire. The eleventh breaks off in the year 312 B. C., but several fragments of the latter half of the history are preserved in the collection of Constantine Porphyrogennetus, and to these a valuable addition was made in 1816 by Mai, from an old MS. Besides, the first three books of Appian were founded entirely upon Dionysius; and Plutarch's biography of Camillus must also be considered as a compilation mostly taken from the Roman Antiquities, so that perhaps upon the whole we have not lost much of this work. With regard to the trustworthiness and general value of Dionysius's history, considerable doubts may be justly entertained; for though he has evidently written with much greater care than Livy, and has studied Cato and the old annalists more diligently than his Roman contemporary, yet he wrote with Several tyrants succeeded each other in Syracuse, until an object which at once invalidates his claim to be conDionysius himself came and retook it about 346. Diony-sidered a veracious and impartial historian. Dionysius sins, however, instead of improving by his ten years' exile, wrote for the Greeks; and his object was to relieve them had grown worse; having usurped the supreme power in from the mortification which they felt at being conquered Locri, he had committed many atrocities, had put to death by a race of barbarians, as they considered the Romans to several citizens, and abused their wives and daughters. be; and this he endeavoured to effect by twisting and (Justinus, Ælianus.) Upon his return to Syracuse, his forging testimonies and botching up the old legends, so as cruelty and profligacy drove away a great number of people, to make out a prima facie proof of the Greek origin of the who emigrated to various parts of Italy and Greece, whilst city of Rome, and he inserts arbitrarily a great number of others joined Iketas, tyrant of Leontini, and a former friend set speeches, evidently composed for the same purpose. He P. C., No. 531 VOL. IX.-B indulges in a minuteness of detail which, though it might be some proof of veracity in a contemporary history, is a palpable indication of want of faith in the case of an antient history so obscure and uncertain as that of Rome. With all his study and research, Dionysius was so imperfectly acquainted with the Roman constitution that he often misrepresents the plainest statements about it. (Niebuhr, Hist. Rome, vol. ii. p. 13, Engl. tr.) For instance, he imagines that the patricians had all the influence in the centuries, and that the plebeians and equites had nothing to do with the first class. (Antiq. vii. 82-87, x. 17. See Niebuhr, Hist. Rome, ii. p. 178, Engl. tr.) He thought the original constitution of Rome was a monarchical democracy, and calls the curies the demus (dñpoc.) He believed when he wrote his second book that the decrees of the people were enacted by the curies and confirmed by the senate (Antiq. ii. 14), and not, as he afterwards discovered, the converse. (Antiq. vii. 38.) In a word, though the critical historian may be able to extract much that is of great importance for the early history of Rome from the garbled narrative and the dull trifling of Dionysius, he cannot be regarded as a meritorious writer, or recommended to the student of antient history as a faithful guide. Dionysius also wrote a treatise on rhetoric; criticisms on the style of Thucydides, Lysias, Isocrates, Isæus, Dinarchus, Plato, and Demosthenes; a treatise on the arrangement of words, and some other short essays. His critical works are much more valuable than his history, and are indeed written with considerable power. The criticism on Dinarchus [DINARCHUS] displays good sense and judgment, and shows the great pains which the author took to separate the genuine writings of the Attic orators from the fabrications which passed under their name. The best editions of Dionysius are those of Hudson, Oxon., 1704, 2 vols., in folio; and by Reiske, Lips., 1774-1777, 6 vols., in 8vo. Mai's fragments were first published at Milan in 1816, and reprinted the following year at Frankfort. They also appear in the second volume of Mai's Nova Collectio, Rome, 1827. His rhetoric has been published separately by Schott, Lips., 1804, 8vo.; and his remarks on Thucydides by Krüger, Hal. Sax., 1823, 8vo. There is a German translation of the Roman Antiquities by J. Lr. Benzler, Lemgo, 1771-1772, 2 vols., 8vo. The only English translation of the Antiquities is the following: The Antiquities of Dionysius Halicarnassensis, translated into English, with notes and dissertations, by Edward Spelman, Esq.,' 2 vols., 4to., London, 1748. DIONYSIUS of Byzantium lived before the year A.D. 196. His voyage ('Avárλove) in the Thracian Bosporus was extant in the 16th century, for Gyllius, who died in 1555, has given extracts in Latin from it in his work on the Thracian Bosporus. A single fragment from this work is printed in Ducange's 'Constantinopolis Christiana,' and in Hudson's Minor Greek Geographers. Perhaps there is some confusion between this Dionysius and the author of the • Periegesis,' whom Suidas (Atovúσiog) calls a Corinthian. DIONY'SIUS PERIEGE'TES, the author of a Greek poem in 1186 hexameter verses, intitled Tns Oikovμivn Пepinуnois, or a description of the habitable world.' It is not known where Dionysius was born nor where he lived. Perhaps the most probable opinion is, that he was a native of Byzantium and belonged to the latter part of the third or the beginning of the fourth century A. D. As a poem the Periegesis is of little value, and as a geographical work, not worth the trouble of reading. The commentary of Eustathius on the Periegesis possesses some value for the miscellaneous information which is scattered through it. There are two Latin translations of this poem, one by Rufus Festus Avienus, and the other by Priscianus. There are numerous editions of Dionysius. The last and best edition of the Periegesis is by G. Bernhardy, Leipzig, 1828, 8vo., in the first volume of his Geographi Græci Minores.' DIOPHANTUS, a native of Alexandria, the exact date of whose birth is unknown, some authors asserting that he lived in the reign of Augustus, whilst others place him under Nero, or even the Antonines. The fact is that we do not know when he lived. He lived however, as is well ascertained, to eighty-four years of age. Diophantus left behind him thirteen books of Arithmetical Questions, of which however only six are extant; but from their distinct and peculiar character, in comparison with all the other writings of the Greek mathematicians, these books have given rise to much discussion. It is how ever scarcely to be conceived that whilst the cumbrou machinery of common language constituted the sole instru ment of investigation, the very curious conclusions which we find in this work could have resulted fron the researche of one single mind. To suppose that Diophantus was the inventor of the analysis which bears his name, is so con trary to all analogy with experience and the history o mental phenomena, as to be utterly impossible to admit Still, if we inquire into the history of this branch of analysis, and ask who were the predecessors of Diophantus, or whether they were Greeks or Hindus, no satisfactory answer can be given. Diophantus also wrote a book on Polygon Numbers (p Toλvywvwv åpμwv). Holzmann published at Basle, in 1575, folio, a Latin translation of both the works of Diophantus. The first Greek edition was by Meziriac, Paris, 1621, folio: an improved edition of Meziriac's edition was published by S. de Fermat, Toulouse, 1670, folio. A valuable translation of the Arithmetical Questions into German was published by Otto Schulz, Berlin, 1822, 8vo.; to which is added Poselger's translation of the work on Polygon Numbers. DIOPSIDE, a variety of PYROXENE. DIO'PSIS, a genus of Dipterous Insects of the family Sepsidæ. The insects of this genus are remarkable for the immense prolongation of the sides of the head. The head itself is small, and appears as if it were furnished with two long horns, each having a knob at its apex; these hornlike processes however are not analogous to the parts usually termed antennæ, but are in fact prolongations of the sides of the head, the knob at the apex of each being the eye of the insect. They vary in length according to the species. In some they are almost equal to the whole length of the insect, whereas in others they are only about half that length. The antennæ are situated close to the eyes, and are three-jointed: the basal joint is the smallest and is very short; the terminal joint is the largest, of a globular form (or nearly so), and furnished towards the apex with a simple seta; there is also a short seta on the peduncle or eye-stalk. situated about midway between the base and the apex of that process, and on the anterior part. The thorax is somewhat attenuated anteriorly, but approaches to a spherical form, and is generally furnished with two spines on each side; the scutellum is also furnished with two spines. The body is more or less elongated, sometimes nearly cylindrical, but generally increases in diameter towards the apex. The legs are tolerably long-the anterior femora are generally thick, and furnished beneath with minute denticulations, and the four posterior femora are often furnished with a spine at their apex. For a detailed account of these curious insects we refer our readers to Mr. Westwood's excellent paper in the seventeenth volume of the Transactions of the Linnæan Society,' in which twenty species are described. H Diopsis Sykesii, G. R. Gray. a denotes the natural size. The illustration is copied from one of that gentleman's figures, and represents the Diopsis Sykesii, one of the largest species of the genus, and which has been selected as possessing the longest eye-stalks; these processes in this insect are of a pitchy red colour, and the body is of the same tint. The head and thorax are black and the wings are clouded with brown. But little is known of the habits of these insects. Lieut.Colonel W. H. Sykes, who collected great numbers of the above species during his residence in India, furnished Mr Westwood with the following notice respecting their habitat and habits:- 'Habitat. The hill fort of Hurreechunderghur, in the western ghauts of the Deccan, at an elevation of 3900 feet above the level of the sea, 19° 23′ N. lat., 73° 40′ E. long. This insect affects chasms or ravines in the lofty woods Thich encircle the mountain in belts. In various places, where the sunbeams occasionally pierce the woods and fall upon isolated or salient rocks in the above localities, they are seen in myriads, either poising themselves in the rays, or reposing on the spots on which the rays fall.' In addition to this notice we may add that all the known species are from the tropical parts of the Old World. DIOPTASE or emerald copper, a crystallized silicate of copper, the primary form of which is a rhomboid; its colour varies from emerald to blackish green; its lustre is vitreous; it is translucent, and sometimes transparent; it is sufficiently hard to scratch glass, though but feebly; it is brittle; specific gravity 3.278; the streak is green; fracture uneven: and cross fracture flat conchoidal. It is found in Siberia and the Bannat; and, according to Lowitz, it consists of silica 33, oxide of copper 55, water 12. DIOPTRICS. [OPTICS; REFRACTION.] DIORA'MA, from the Greek word dopav, to see through, a mode of painting and scenic exhibition invented of late years by two French artists, Daguerre and Bouton, which, although it does not possess some of the advantages of the panorama, produces a far greater degree of optical illusion. It has also one advantage over the panorama, in being equally suitable for architectural and interior views as for landscape; nay even more so, because the positive degree of light is more natural, and the relief of the objects becomes more deceptive. The peculiar and almost magical effect of the diorama arises, in a considerable measure, from the contrivance employed in exhibiting the painting, which is viewed through a large aperture or proscenium. Beyond this opening the picture is placed at such distance that the light is thrown upon it, at a proper angle, from the roof, which is glazed with ground glass, and cannot be seen by the spectator. Besides the light being thus concentrated upon the picture, the effect is materially increased by the spectator being in comparative darkness, receiving no other light than what is reflected from the surface of the painting itself. Another circumstance greatly favouring illusion is the intervening distance; and also the circumstance that the sides of the proscenium or opening are continued inwards to wards the picture, so as to screen its extremities, and at the same time assist in confining the light to the scene itself. The contrast thus occasioned, and the exclusion of all otner | objects of vision save those represented in the painting, so that the eye has no immediate standard of comparison between them and real ones, give to this species of exhibition such extraordinary force that a very moderate degree of light will suffice to show the painting. Hence the light may be diminished or increased at pleasure, and that either gradually or suddenly, so as to represent the change from dinary daylight to sunshine, and from sunshine to cloudy weather, or to the obscurity of twilight; also the difference of atmospheric tone attending them: all which variations give * the diorama a character of nature and reality beyond that of any other mode of painting. These transitions, in regard to light and atmospheric effects, are produced by means of fferent folds or shutters attached to the glazed ceiling, which are so contrived that they may be immediately pened or closed to any extent, thereby increasing or dimiishing the light just as required, and otherwise modifying t. Further than this, some parts of the painting itself are transparent, and on them the light can occasionally be aditted from behind, thereby producing a brilliancy far exreeding that of the highest lights of a picture upon an epaque ground, which can be made to appear vivid and sparkling only by contrast, not by any positive increase of light on those parts of the surface. Here, on the contrary, such augmented light is admitted through it, in addition to that which illuminates the picture generally, an artifice which secures the advantages of painting in transparency without its defects; the objects looking more solid, and the effect being altogether more natural than when the whole of the light passes through the picture. The combination of transparent, semi-transparent, and opaque colouring, still further assisted by the power of varying both the effects and the degree of light and shade, renders the diorama the most perfect scenic representation of nature, and adapts it peculiarly for moonlight subjects, or for showing such accidents' in landscape as sudden gleams of sunshine and their disappearance. It is also unrivalled for showing architec | ture, particularly interiors, as powerful relief may be ob The spectatory or saloon for the visitors is a rotunda 40 feet in diameter, with a single opening or proscenium about 20 feet wide; and placed within another rotunda having two openings communicating with the picture-rooms, each of which contains a view. When a change of scene takes place the inner rotunda is turned by means of machinery beneath the floor, till the proscenium is gently shifted from the opening into one picture-room to that of the other, the two being quite contiguous. At the next change it is shifted back again, so that the whole space passed over backwards and forwards is about one-third of the entire circumference, or double that portion of the circle forming the proscenium. The diorama at Berlin, executed by Carl Gropius, an eminent scene-painter, is somewhat on the same plan, yet with some slight differences. The peculiar mode just described, of turning the spectatory from one painting to the other, is adopted, as the scenes are much larger than the opening through which they are viewed, and require to be stretched on a framing, so that they cannot be either rolled up, or drawn aside in two halves, as is done with scenes of a theatre. Nevertheless, it would perhaps be found practicable to exhibit a succession of three or four views, in a single 'picture-room,' by making that part of the building sufficiently spacious to allow each scene to be slided backwards or forwards, so as to be entirely out of view when drawn aside. DIOSCO'REA, the genus of plants which furnish the tropical esculents called yams. They are perennial fleshyrooted or tuberous dioecious plants, with annual twining stems, broad alternate leaves having a somewhat netted arrangement of their veins, and loose clusters of small green flowers. The corolla and the calyx taken together consist of six small equal segments, which, in the females, stand upon the top of the ovary. The male flowers have six stamens; the females three styles. The seed vessel is a thin compressed three-winged capsule, containing one membranous seeds. or two The only general account of the species, which at all deserves to be consulted, is that of Dr. Roxburgh, who cultivated seventeen sorts in the Botanic Garden, Calcutta ; others are known to botanists, but far from perfectly. Be The common West India yam, which is often sold in the shops of London, is produced by Dioscorea alata. It is met with in the East Indies also, but only in a cultivated state. A figure of it is given in Rheede's 'Hortus Malabaricus,' vol. vii. t. 38, under the name of katsji-kelengu. Its tubers are oblong, brown externally, white internally, and often of great size, weighing sometimes as much as 30lbs.; they perish after the first year, if left in the ground, having first produced the young ones that are to replace them. sides the tubers the proper roots of all these plants are fibrous, springing from and chiefly about the union of the stems with the tubers, and spreading in every direction. The stems are furnished with four crested leafy wings, and spread to a great extent twining round trees and bushes; they often bear prickles near the ground. The first leaves that appear on the stem are alternate, the succeeding are opposite, seated on long stalks, deeply heart-shaped at the base, sharp-pointed, smooth, with from five to seven ribs. The flowers are small and green, and appear in compound panicles. The remainder of the species are very similar to this in general characters; a few short notes will sufficiently indicate their differences. D. globosa, cultivated in Bengal under the name of choo puree aloo, is most esteemed of the Indian yains. Its flowers are highly fragrant; the tubers are white internally; the leaves arrow-headed. D. rubella, the guranya-aloo, is another Indian sort with large tubers stained with red immediately below the cuticle; it is much esteemed; its tubers are sometimes three feet long; its flowers are fragrant. Another valuable kind is D. purpurea, called lal-guranyaaloo in Bengal, whose tubers are permanently stained purple throughout. At Malacca is cultivated another purple-rooted sort, the D. atropurpurea, whose tubers are large and irregular, and grow so near the surface of the ground as to appear in dry weather through the cracks that they make in the soil by raising the earth over them. Other eatable sorts are numerous, but are less valuable, and therefore not cultivated. In Otaheite the D. bulbifera, which bears small fleshy angular tubers along the stem in the axils of the leaves, is the favourite species. It is not a little remarkable that while so many species are nutritious in this genus, some should be highly dangerous; but such is unquestionably the fact. Dioscorea Dæmonum and triphylla, both ternate leaved species, have dreadfully nauseous and dangerous tubers. No genus is more in want of revision than this. | ing plants with diligence and acquainting himself wit their properties, real or reputed. He also gathered togethe the opinions current in his day concerning the medica plants brought from countries not visited by himself, espe cially from India, which at that time furnished many drug to the western markets. From such materials he compile his celebrated work on Materia Medica, in five books wherein between 500 and 600 medicinal plants are name and briefly described. He is moreover reputed the autho of some additional books on therapeutics, &c.; but in th judgment of Sprengel the latter are spurious, and from the mixture of Latin and Greek names of plants, are probabl some monkish forgery. DIOSCOREA'CEE, a natural order of endogenous plants, referred to the Retose group, and having the last genus for their type. They are particularly distinguished by the following character. Flowers dicecious; calyx and corolla superior; stamens six; ovary three-celled, with one or two-seeded cells; style deeply trifid; fruit leafy, compressed, occasionally succulent; embryo small, near the hilum, in a large cavity of cartilaginous albumen. All the species are twining shrubs, with alternate or spuriously opposite leaves. They consist, with the exception of Tamus, or Black Bryony, of tropical plants, or at least of such as require a mild frostless climate. Some of them produce eatable farinaceous tubers, or yams, as the various species of Dioscorea and Testudinaria; but there is a dangerous acrid principle prevalent among them, which renders the order upon the whole suspicious. It exists in a perceptible degree in Tamus, and is still more manifest in the three-leaved Dioscorea. Few books have ever enjoyed such long and universa celebrity as the Materia Medica of Dioscorides. For six teen centuries and more, to use the words of one of hi biographers, this work was referred to as the fountain-head of all authority by everybody who studied either botany o the mere virtues of plants. Up to the commencement o the seventeenth century the whole of academical or privat study in such subjects was begun and ended with the work of Dioscorides; and it was only when the rapidly increasing numbers of new plants and the general advance in al branches of physical knowledge compelled people to admi that the vegetable kingdom might contain more thing than were dreamt of by the Anazarbian philosopher, that his authority ceased to be acknowledged. 1, a shoot of Rajania cordata; 2, a male flower; 3, a female flower; 4, a portion of a ripe fruit with the seed exposed; 5, a section of the seed. This is the more surprising, considering the real nature of these famous books. The author introduced no order into the arrangement of his matter, unless by consult ing a similarity of sound in the names he gave his plants Thus, medium was placed with epimedium, althæa can nabina with cannabis, hippophæstum (cnicus stellatus) with hippophae, and so on; the mere separation of aro matic and gum-bearing trees, esculents and corn-plants, hardly forms an exception to this statement. Of many of his plants no description is given, but they are merely designated by a name. In others the descriptions are com parative, contradictory, or unintelligible. He employs the same word in different senses, and evidently attached no exactness to the terms he made use of. He described the same plant twice under the same name or different names; he was often notoriously careless, and he appears to have been ready to state too much upon the authority of others. Nevertheless, his writings are extremely interesting as showing the amount of Materia Medica knowledge in the author's day, and his descriptions are in many cases far from bad: but we must be careful not to look upon them as evidence of the state of botany at the same period; for Dioscorides has no pretension to be ranked among the botanists of antiquity, considering that the writings of Theophrastus, four centuries earlier, show that botany had even at that time begun to be cultivated as a science distinct from the art of the herbalist. DIOSCO'RIDES, PEDA'CIUS, or PEDA'NIUS, a Greek writer on Materia Medica, was born at Anazarbus, in Cilicia, and flourished in the reign of Nero, as appears from the dedication of his books to Areus Asclepiadeus, who was a friend of the consul Licinius or Lecanius Bassus. In early life he seems to have been attached to the army; and either at that time or subsequently he travelled through Greece, Italy, Asia Minor, and some parts of Gaul, collect. The most celebrated MS. of Dioscorides is one at Vienna, illuminated with rude figures. It was sent by Busbequius, the Austrian Ambassador at Constantinople, to Mathiolus, who quotes it under the name of the Cantacuzene Codex, and is believed to have been written in the sixth century. Copies of some of the figures were inserted by Dodoens in his Historia Stirpium, and others were 'engraved in the reign of the empress Maria Theresa under the inspection of Jacquin. Two impressions only of these plates, as far as we can learn, have ever been taken off, as the work was not prosecuted.' One of them is now in the Library of the Linnæan Society; the other is, we believe, with Sibthorp's collection at Oxford. They are of little importance, as the figures are of the rudest imaginable description. Another manuscript of the 9th century exists at Paris and was used by Salmasius; this also is illustrated with figures, and has both Arabic and Coptic names introduced, on which account it is supposed to have been written in Egypt. Besides these, there is at Vienna a manuscript believed to be still more antient than that first mentioned, and three others are preserved at Leyden. The first edition of the Greek text of Dioscorides, was published by Aldus at Venice, in 1499, fol. A far better one is that of Paris, 1549, in 8vo. by J. Goupyl; but a better still is the folio Frankfort edition, of 1598, by Sarracenus. Sprengel laments, nullum rei herbariæ peritum virum utilissimo huic scriptori operam impendisse. Nevertheless, there have been many commentators, of whom some, such as Fuchsius, Amatus Lusitanus, Ruellius, Ta |