000 inhabitants; but owing to the predatory disposition of the Koords, who by their attacks have rendered unsafe the intercourse with Bagdad and Aleppo, its prosperity has declined, and it now contains no more than 40,000 inhabitants, the greater part Turkish, the rest mostly Armenian. Some trade is, however, carried on with Aleppo, and the manufacture of cotton and silk goods, though much diminished, is still continued. The streets, like those of other eastern cities, are narrow and dirty, and most of the houses are constructed of rough stone covered with a plaster composed of mud and straw. The town contains many mosques, an Armenian cathedral and other Christian churches, numerous baths, caravansaries, and bazaars, and is well supplied with water, which is introduced by a fine aqueduct, and distributed through the city in numerous stone fountains. The walls are built of a dark-colored basalt, quarried in the neighborhood, and many of the principal buildings of the city are constructed of the same material, whence the Turks call the place Kara Amid, or Black Amid; Amida being the ancient name of the town. A British consul resides here.

DIARRHEA (Gr. diappew, to flow through), a disease characterized by the occurrence of frequent, loose, alvine discharges. In a proper system of nosology diarrhoea would scarce find a place; it is a symptom rather than a disease, and is produced by a number of different pathological conditions. It is present in the course of typhoid fever, is a frequent accompaniment of phthisis, and is sometimes an attendant upon albuminuria and other forms of blood poisoning; it is caused by inflammation and ulceration of the bowels. Those slighter forms of the complaint only will be noticed here which are independent of constitutional causes, and which are produced by a temporary irritation or sub-inflammation of the intestinal mucous membrane. Diarrhoea is often caused by the use of crude and indigestible food, or even by food ordinarily wholesome taken in too great quantity or variety. Fruit, particularly when acid and unripe, uncooked vegetables, as cucumbers and salads, food in a state of incipient decomposition, the flesh of immature animals, as young veal, &c., are all liable to act upon the bowels. Certain articles, as mushrooms, shellfish, the richer varieties of ordinary fish, as salmon, from peculiarity of habit disagree with particular individuals and produce diarrhoea. The same is true of a total change of diet; food perfectly wholesome to those accustomed to it, and the water used habitually in certain districts of country, often cause bowel complaints in the stranger. Emotions of the mind, particularly grief and anger, in some persons promptly occasion an attack of diarrhoea; others are affected in the same way by sudden changes of temperature, wet feet, or exposure to cold. Where diarrhoea is caused by the ingestion of food rendered irritating by its quantity or quality, the purging itself soon removes the cause of irrita

tion and the diarrhoea ceases; if this should not be the case, a moderate opiate or an anodyne combined with an astringent are all that will be found necessary. When diarrhoea is dependent on exposure to cold, a bland, unirritating diet, the warm bath, and the use of opium or of opium and ipecacuanha in small doses, may be had recourse to; in such cases the patient is generally benefited by wearing a flannel bandage around the abdomen.-Young infants at the breast sometimes suffer from bowel complaint; here it is commonly caused by over-feeding. Ordinarily nature provides against this by the facility with which the infant vomits; the stomach frees itself from the excess of food, and no mischief is done; but when the infant does not vomit, diarrhoea is caused, and undigested curd is present in large quantity in the evacuations. The obvious remedy is a prolongation of the intervals at which the child is suckled. During dentition in infants, from the large quantity of blood sent to the digestive organs, and the rapid evolution which they are undergoing, the bowels are irritable, and diarrhoea often supervenes; this is best guarded against by care in the diet and a proper observance of hygienic regulations. The severer forms of the complaint which occur in large cities, from the combined effect of an impure atmosphere and the excessive heat of our summers, are spoken of under the head of CHOLERA INFANTUM.

DIAS, A. GONÇALVEZ, a Brazilian poet, born in Caxias, Aug. 10, 1823. He was educated in Portugal, and returning to his native country, published at Rio de Janeiro in 1846 a volume of poems entitled Primeiros cantos, which was followed by his drama of Leonor de Mendonça (1847), Segundos cantos (1848), and Ultimos cantos (1850). In 1848 he was chosen profes sor of national history in the college of Don Pedro II.; in 1850 he was sent on a scientific mission to the provinces bordering on the Amazon; on his return he was employed in the office of the minister of foreign affairs, and in 1855 was charged with a scientific mission to Europe. His poetry is exceedingly popular in Brazil.

DIAS, BARTHOLOMEO, & Portuguese navigator, born in the latter part of the 15th century, lost in a storm at sea, May 29, 1500, while on his way from Brazil to India. In 1486 he sailed on an expedition to explore the W. coast of Africa, and without knowing it was carried around the southern point of the continent and landed at the mouth of Great Fish river, where he discovered that he was on the E. coast. The stormy cape he called Cabo Tormentoso, a name which the king of Portugal changed into Cape of Good Hope. Dias subsequently sailed on another African expedition under Vasco da Gama, and he commanded one of the vessels in the fleet with which Cabral discovered Brazil. It was on this expedition that he perished.

DIAS, HENRIQUE, a Brazilian general, born st Pernambuco at the beginning, died in the latter part of the 17th century. He was a freed negro, who by his superior attainments rose in 1639 to

DIASTASE

the supreme command of the colored soldiery of the Brazilian army. He took a conspicuous part in the protracted warfare which finally led to the overthrow of Dutch supremacy in Brazil. DIASTASE (Gr. diorημ, to separate). When the grain of wheat, oats, or barley begins to germinate, there is formed at the base of the sprout a peculiar nitrogenous compound, very soluble in water, called diastase, the exact composition of which has never been determined. It is also found in the germ of the potato. It seems to be gluten in an altered form. By the action of this substance and of acetic acid, which also now first appears in the seed, the mucilaginous substance called dextrine, formed from the starch of the grain, is converted into starch sugar. This by fermentation passes into alcohol. It is therefore an essential element for the process of brewing. It may be obtained by digesting bruised barley malt with a little cold water, then expressing it through cloth. The liquor is then treated with sufficient alcohol to destroy its viscidity and cause the albumen to separate. This is removed by filtration. An additional quantity of alcohol then throws down the diastase in an impure state. It is redissolved in water and again precipitated with alcohol. When separated and dried, it is a white, tasteless, solid substance, without action upon gum or sugar, but capable at a temperature of 160° of converting starch suspended in water into dextrine, and this into grape sugar. One part of dextrine, it is found, is sufficient to cause 2,000 parts of starch to undergo this change.

DIATHERMANCY AND ATHERMANCY. The various dispositions of light entering the substance of different bodies are familiar. Some bodies, extinguishing the light, are termed opaque; others, through which it passes without sensible diminution, transparent, or diaphanous; but in most media both diaphaneity and extinction occur, in degree. Results entirely similar are now found to hold in the case of heat. All may observe that the sunbeams after passing through the air or through window glass are still very sensibly warm, while the glass and the air may remain at the same time in a great degree unwarmed. By a double convex lens of ice, the heat of the solar beam has been brought to a focus, and gunpowder and other combustibles fired, while the ice itself remained quite unaffected by the heat passing through it. A pane of glass held before a fire, however, stops the transmission of the heat striking it, and becomes warmed. From these facts, we conclude that from sources of heat there proceed outward on all sides rays of heat, just as from luminous bodies we have light rays; moreover, that there are media, as the air, which transmit heat rays freely, while others arrest (or, as it is often with doubtful propriety phrased, absorb) these rays; still a third class of bodies both transmitting and arresting portions of them. Bodies of the first of these classes are termed diathermanous; those of the second, athermanous; those of the

VOL. VI.-29

third are imperfectly diathermanous. These subjects were first investigated in 1811-'12, by M. Prevost of Geneva, and M. de la Roche in France, but our knowledge of them is mainly due to M. Melloni, who began in 1832 a series of remarkable investigations, which won for him from M. de la Rive the title of "the Newton of heat." These researches, determining as they did the transmission of an invisible agent, heat, and often in degrees far too feeble to be detected by the nicest sensibility of the hand or by the ordinary means, would have been impossible but for the invention, by Nobili and Melloni, of a new thermoscopic apparatus, consisting of a thermo-electric pile connected with a highly sensitive galvanometer; the delicacy of the arrangement being such that if, in a room at ordinary temperatures, the human hand were presented in a line with the apparatus and at the distance of several feet, the heat radiating from the hand would cause the needle to be sensibly deflected. Some of the results discovered with the aid of this apparatus will be briefly stated. A plate or crystal of rock salt, even if an inch in thickness, was found, after diminishing the incident heat 7.7 per cent. by reflection, to transmit the entire remainder; this body, only, arrested within its substance no sensible portion of the heat rays. Hence, rock salt has been styled the true glass for heat; and its permeability by heat exceeds even that of glass by light. Smoked, or coated with soot, so as to be quite opaque, this body still allowed many of the heat rays to pass through it; and the same was true of smoked quartz and black glass. But citric acid, alum water, and limpid candy, although quite transparent, almost totally arrested the heat of the sun, of a flame or other source of intense heat, while they cut off entirely the rays from bodies raised to about red heat, and of all temperatures below. Bodies are not, therefore, diathermanous in proportion as they are transparent. But the amount of transmission of heat rays is found to depend on at least 4 particulars: 1, the nature of the source of heat; 2, the intensity of heat of the source; 3, the nature of the medium; and 4, its thickness. Solar heat has the greatest penetrating power; that of bodies in an incandescent state passes through the same medium in greater quantity than that of bodies at a dark heat; while of the heat of naked flame rock salt transmits 92.3 per cent., Iceland spar passes 39, white topaz 33, and alum 9 per cent.; and up to a certain thickness in every case, the amount transmitted diminishes with increase of thickness of the medium. Beyond a certain increase of the number or thickness of the plates, however, the diminution of heat ceases. The heat rays that can get through the first half inch or inch of glass, for example, will then go on undiminished through a much greater distance; so that it seems that certain heat rays are sifted out by each medium, as being incapable of moving through it with freedom; the others

then pass on. If, again, the heat beam which suffers no more loss by going through glass be now received in rock crystal, in the first part of this medium it suffers a remarkable diminution; other rays are sifted out, and a diminished beam passes. The same thing happens with light in colored media. The sunbeam in going through a certain depth of a red glass or solution has its bluish green rays sifted out and extinguished; the remainder, on being passed into a bluish green medium, is lost in like manner; a feeble beam only escapes, or none at all. Hence, the heat beam, like the beam of light, is regarded as a sheaf of heat rays of varying degrees of refrangibility; or we have a true heat spectrum. Dark and feeble sources of heat, it is found, emit rays analogous to blue and violet rays of light (Whewell), and highly luminous sources such as are analogous to yellow and red rays. The former, however, are proved to be the less refrangible heat rays; so that it is the more refrangible heat rays which are the more transmissible. This department of the subject has received the name of thermochrosy, or heat coloration. In this view, then, rock salt is a body quite colorless to heat; while alum, water, ice, and some other transparent bodies, are nearly heat-black. The true heat color of water, however, is dark red, since the few rays it transmits are of the more refrangible class; and if this beam be received in a glass tinged green with copper, and the heat color of which may be considered blue, the remaining rays are lost; the heat beam is entirely arrested, though a greenish light still passes. This combination is then, apparently, a total black for heat. Where it is required to admit light without heat, therefore, this combination, or, as ordinarily more convenient, a solution or plate of alum, may be made the medium; where heat is to be admitted without light, smoked rock salt or black glass serves the purpose. In some operations in the arts, workinen exposed to an intense heat protect their faces to a good degree by wearing a glass mask.

DIATOMACEÆ, minute plants growing in moist situations, in collections of fresh water or in the sea, consisting of frustules of various forms, the walls of which contain a large quantity of silex, and are often beautifully diversified and marbled by striæ or by dots. Notwithstanding the general resemblance of these curious vegetations to the species of desmidies, they are clearly made distinct by the flinty fronds, singular striation, and absence of green coloring matter. Agardh asserts that many of these organisms have as much affinity with the mineral kingdom as with the vegetable, being in fact vegetable crystals, bounded by right lines and collected into a crystalliform body, and having no other difference from minerals than that the individuals have the power of again separating from each other. As in the case of the desmidiem, there are solitary species, and others grouped so as to form lines and membranes. In some, the production of new plants

from spores presents the same dissimilarity between the young and the adult forms. There are also numerous genera which can be accurately distinguished not only by the difference of form or outline, but by their own peculiar striations, markings, and dots. Both in the single and associated species there is a distinct pellucid peduncle or footstalk. This is sometimes considerably dilated above, or else forked, sometimes repeatedly. In this case, each frustule remains attached, the base dilating as may be required. This arrangement gives a fan-like appearance of great beauty. But in the threadlike species it is only the corners that remain attached; as no stem or footstalk is visible here, it has been conjectured that it exists only in those plants which have grown from spores or in the seedling forms. Certain channels or apertures are so arranged as to convey the water to the inner cellular membranes, and thus to afford nutriment, The same curious conjugation to be seen in other algae has been detected in the diatomaces by Thwaites, and has been confirmed by Berkeley and Broome. It is computed that vast areas of solid earthy matter are due to the growth, presence, and decay of these minute organisms. Many of the most beautiful are found in the guano of commerce, doubtless swallowed in the food of birds, and still remaining in perfect preservation. In the United States, masses of several inches in thickness are found on the bottom of ponds, composed of myriads of these organisms, which on being exposed to desiccation become as white and friable as chalk. Even peat bogs and meadows abound with them. The polishing powders sold under the name of Tripoli are composed of these natural silicious fragments. The soundings on the shores of Victoria Barrier, in water whose average depth is 1,800 feet, were found by Dr. Hooker to be invariably charged with diatomaceous remains. These fossil species are often so identical with recent ones, that it were scarcely too extravagant to admit the assertion of Ehrenberg, that species are to be found in a living state in situations where they have been propagated from times far anterior to the existence of man. The United States are rich in the diatomaceæ, both fossil and living. We are indebted to the perseverance and scientific skill of the late Prof. J. W. Bailey, of West Point, N. Y., for a list and arrangement of species detected by him. In the tertiary infusorial stratum of Richmond, Va., Ehrenberg detected 20 genera and 46 species, of which all were also European excepting two. This group of American forms is of peculiar interest, because the strata at Richmond are decidedly of marine origin, and consequently give at once a general view of these marine microscopic forms along the North American coast. We shall briefly notice, in conclusion, some of the most remarkable of these vegetable organisms occurring in the United States and not uncommon in Europe. Of the perfectly free diatoms we have many species of naviculaceae remarkable for beauty,

DIATOMACEÆ

symmetry, delicacy, or else for their striations. The largest, most common, and most easily distinguished, is N. viridis, found in every ditch and pond, of an oblong outline. It can be detected in great abundance in the ashes of peat, and in the deposits of infusorial earths. Its length is about of a line. Several of a sigmoid outline are very remarkable for the delicacy of their striæ, of which may be mentioned pleurosigma Baltica, P. hippocampus, but more particularly P. angulata. The lines of striation upon Nitzschia sigmoidea are about Joo of an inch apart. In fragilaria we have long threads of frustules adhering with considerable firmness at their commissures; but in diatoma they adhere only at a single point, so as to form curious chains of divided or separated joints. Prof. Bailey describes bacillaria paradora as a very interesting species, presenting by its curious motions and its paradoxical appearance an object well calculated to astonish all who behold it. At one moment the needle-shaped frustules lie side by side, forming a rectangular plate; suddenly one of the frustules slides forward a little way, the next slides a little also, and so on through the whole number, each, however, retaining a contact through part of its length with the adjoining ones. By this united motion the parallelogram is changed into a long line; then some of the frustules slide together again, so that the form is then much like a banner. Similar motions are constantly going on, and with such rapidity that the eye can scarcely follow them. The cause of this motion is wholly unknown, but it is most probably mechanical and not vital. Mr. Smith, in his work on the diatomaceæ, estimates this motion as being inch per second. In meridion vernale we have one of the most beautiful of the freshwater diatoms. It consists of spiral or helicoidal chains, to perceive which the specimens must be tilted on edge. It occurs in immense quantities in mountain brooks, covering every submerged stone, or twig, or spear of grass, in the early days of spring. Among the groups with vittate or ribbon-like fronds, we may notice striatella arcuata, occurring in vast quantities on the filiform marine algæ, and covering them so much oftentimes as to make them glitter in the sunbeams as if invested with crystals. In still another natural group, where the stria are no longer visible in the frustules or fronds, we find a multitude of microscopic objects, furnishing sources for fresh admiration whenever they are examined. In some of these the fronds, which are disciform, are marked with radiating lines, of which coscinodiscus, very common in a fossil state in the Richmond earth and elsewhere, is most beautiful. In C. linea tus the cellules of the frond form parallel lines in whatever direction they may be viewed, and C. oculus iridis gives curious colored rings. When perfect, the disk of coscinodiscus is covered with circular spots in rows corresponding with the radii. In consequence of this arrangement

they also form beautiful spiral rows in other directions, so that the curves present no inconsiderable resemblance to patterns produced by. engine-turning; at other times the spots are found to form 3 sets of lines, making angles of 60° and 120° with each other; and on others the spots are disposed without much apparent regularity, frequently having a star-like figure in the centre. The spots are so small on some of the disks as to be almost invisible even by the highest magnifying powers; on others they are quite large and hexagonal. In podiscus Rogerii (Bailey), the whole surface is so beautifully punctate, that no engraving could do it justice. The most complicated markings on the coscinodiscus scarcely rival the elaborate ornaments of this truly elegant organism. It has proved very common in Virginia and Maryland in a fossil condition. The beauty of isthmia obliquata, detected in the mud of Boston harbor, can only be appreciated by ocular examination. The diatomaces enter largely into the food of the mollusca. Dr. Hooker found dictyocha aculeata in the stomachs of salpa taken off Victoria Land, and remains of diatomaceæ occurred in the same ascidiums examined between the latitudes of the N. tropic and 80° S. The medusæ are also in particular often filled with these forms.-See Bailey in "American Journal of Science and Arts," vols. xli., xlvi. ; "Proceedings of Essex Institute," vol. i., pp. 33-48, and vol ii., pp. 70, 71; Smith's "British Diatomacea;" Kützing's Species Algarum (Leipsic, 1849); Berkeley's "Introduction to Cryptogamic Botany" (London, 1857).

DIAZ, MIGUEL, an Aragonese explorer, born in the latter part of the 15th century, died about 1514. He took part in the 2d expedition of Columbus, and having arrived in St. Domingo in 1495, he became involved in a duel which forced him to flee to the southern part of the island, where he married the female ruler of the tribe. From information given by her, and with the cooperation of Bartholomew Columbus, who was governor of the colony, he discovered the gold mines of St. Christopher, and afterward took a conspicuous part in the foundation of Nueva Isabella (afterward St. Domingo) in the vicinity of the gold districts. He faithfully adhered to the cause of Columbus until his death.

DIAZ DEL CASTILLO, BERNAL, a Spanish adventurer and chronicler, born in Medina del Campo, Old Castile, about the close of the 15th century. He went to seek his fortune in the new world in 1514, and joined the expeditions which sailed from Cuba to Yucatan under Fernandez de Cordova in 1517, and under Grijalva in 1518. He afterward attached himself to the fortunes of Cortes, and followed that chief in all his most important battles and marches with distinguished valor and loyalty. In 1568 he was regidor of the city of Guatemala. When Gomara's "Chronicle of New Spain" appeared, Diaz began his Historia verdadera de la conquista de la Nueva España, the object of which was to correct the many

misstatements of his rival, and to claim for himself and his comrades a share of the glory which Gomara gave almost wholly to Cortes. The work was finished in 1558, and though destitute of literary merit, and disfigured by the author's vanity, it nowhere betrays a wilful perversion of truth, and is prized for its simplicity of style. It was first published at Madrid in 1632. An English translation by J. I. Lockhart appeared in 1844. A recent American writer has assailed the authenticity of the narrative, which he attempts to resolve into a collection of fables. (See Wilson's "New History of the Conquest of Mexico," Philadelphia, 1859.) DIBDIN. I. CHARLES, an English song writer and composer, born in Southampton in 1745, died July 25, 1814. He was the 18th child of his parents, who intended him for the church. Following his own inclinations, however, he cultivated the study of music, and at the age of 16 went to London, where at first he supported himself by composing ballads for the music sellers and by tuning pianos. In 1763-4 the opera of the "Shepherd's Artifice," written and composed by him, was produced at Covent Garden theatre, after which he appeared for several years in the joint capacity of actor and composer. Among his most popular works were the "Padlock," the "Deserter," the "Waterman," and the "Quaker," produced at Drury Lane, under the management of Garrick. Having quarrelled with the latter, he was for several years engaged in various theatrical speculations as manager or proprietor, and in 1789 instituted a species of musical entertainment, in which he was the sole author, composer, and performer. So successful did the enterprise prove, that in 1796 he erected a small theatre in Leicester fields, called Sans-Souci, in which he performed until 1805, when he retired from professional life in somewhat embarrassed circumstances, owing to his improvident habits. A pension of £200 was procured for him, of which in 1806 he was deprived by the whig ministry of Lord Grenville. The tory administration, which came into power the succeeding year, restored his name to the pension list, but his improvidence kept him in poverty until his death. His theatrical compositions, 47 of which are enumerated in the "Biographia Dramatica," amount to about 100. Upon his songs, however, of which he is said to have written upward of 1,000, his reputation mainly rests. Most of these were ephemeral productions, and many were below mediocrity; but his nautical songs and ballads are among the finest specimens of their kind in the language; and some of them, like "Poor Tom Bowling," written on the death of his brother Thomas, a sea captain, and "Poor Jack," are established favorites. They were set to simple and expressive melodies, and were exceedingly popular at the beginning of the present century, having, it is said, been influential in supplying the navy with volunteers. He published a history of the stage and some miscellaneous works of no great value. A new edition

of his songs, with a memoir by T. Dibdin, illustrated by George Cruikshank, was published in London in 1850. II. THOMAS, Son of the preceding, born in London in 1771, died there, Sept. 16, 1841. He adopted the profession of his father, and for many years appeared before the public as actor, author, and composer. His songs and dramatic pieces are probably as numerous as those of his father, but are now comparatively forgotten. He died in poverty, while employed in compiling an edition of his father's sea songs, for which he received an allowance from the lords of the admiralty. III. THOMAS FROGNALL, D.D., an English bibliog rapher, nephew of Charles Dibdin, born in Calcutta in 1775, died Nov. 18, 1847. He was educated at Oxford and studied for the law, but afterward took orders. In 1807 he became editor of a weekly journal called the "Director," and in 1809 published in the form of a dialogue his "Bibliomania," reprinted with great enlargements in 1811. In 1818 he travelled abroad, and in 1824 was appointed to the rectory of St. Mary's, Bryanstone square, which he held until his death. In 1814-'15 he published, under the title of "Bibliotheca Spenceriana,” an account of the rare books in Earl Spencer's library, to which he afterward added a description of the earl's seat at Althorp, and an account of the Cassano library purchased by him. The work is often referred to, but is inaccurate. In his latter years Dr. Dibdin was involved in pecuniary embarrassment. His principal works, beside those above mentioned, are: "Typographical Antiquities of Great Britain" (4 vols, 1810-20); "Bibliographical Decameron" (3 vols. 8vo., 1817); Bibliographical, Antiquarian, and Picturesque Tour in France and Germany" (3 vols. 8vo., 1821); “Introduction to a Knowledge of rare and valuable Editions of the Greek and Roman Classics" (4th ed., 2 vols. 8vo., 1827); "Reminiscences of a Literary Life" (2 vols. 8vo., 1886); "Bibliographical, Antiquarian, and Picturesque Tour in the Northern Counties of England and Scotland" (3 vols. 8vo., 1839).

DICE (plural of die), small cubes of ivory, bone, serpentine stone, or close-grained wood, used in gaming. Each of their 6 faces is marked with a different number of points, from 1 to 6, in such a way that the numbers upon any 2 opposite sides together count 7. They are shaken and thrown from a box on to a table, and the game depends upon the number of points presented by the upper faces. This is one of the most ancient of games, and was said to have been invented by the Greeks to divert themselves during the siege of Troy. Plutarch makes it an early invention of the Egyptians, in whose mythological fables it is mentioned. Dice have been discovered in Thebes, made of bone or ivory, and similar to those in use at present. Herodotus ascribes the invention of this, as of all other games of chance, to the Lydians. It is alluded to as a favorite amusement by Eschylus and Sophocles. The chief distinction between the ancient and the modern game is, that in the