nights most favorable for this effect, are those which are the calmest and most serene, and on which the air is so dry as to deposit little dew after midnight. Clouds and frequent changes of wind are certain preventives of congelation. 300 persons are employed in this operation at one place. The enclosures formed on the ground are four or five feet wide, and have walls only four inches high. In these enclosures, previously bedded with dry straw, broad, shallow, unglazed earthen pans are set, containing unboiled pumpwater. Wind, which so greatly promotes evaporation, prevents the freezing altogether, and dew forms in a greater or less degree during the whole of the nights most productive of ice. If evaporation were concerned in the congelation, wetting the straw would promote it. But Mr. Williams, in the 83d vol. of the Philosophical Transactions, says, that it is necessary to the success of the process that the straw be dry. In proof of this he mentions, that when the straw becomes wet by accident it is renewed; and that when he purposely wetted it in some of the enclosures, the formation of ice there was always prevented. Moist straw both conducts heat and raises vapor from the ground, so as to obstruct the congelation. According to Mr. Leslie, water stands at the head of radiating substances.

DEWARCUNDAH, a sterile, or rather a desolated district of Hindostan, province of Golconda, extending along the south side of the river Godavery, and situated between the eighteenth and nineteenth degrees of northern latitude. The country contains the ruins of a number of forts and villages, which evince it to have been formerly well cultivated.

DEW-BORN, in country affairs, a distemper in cattle, being a swelling in the body, as much as the skin can hold, so that some beasts are in danger of bursting. It proceeds from greediness in feeding, when put into a rank pasture; but commonly when the grass is full of water. In this case the beast should be exercised, and made to purge well; but the proper cure is bleeding in the tail; then take a grated nutmeg, with an egg, and breaking the top of the shell, put out so much of the white as that you raay have room to slip the nutmeg into the shell; mix them together, and then let shell and all be pu down the beast's throat; that done, walk him up and down, and he will soon mend.

DE WITT (John), a celebrated Dutch statesman, born in 1625, at Dort. At the age of twenty-three, he published Elementa Curvarum Linearum; and, after taking his degrees, became, in 1650, pensionary of Dort, and distinguished himself very early in the management of public affairs. He opposed the war with the English

In

as injurious to the States; and when the event justified his predictions, he was unanimously chosen pensionary of Holland. In this capacity he labored to procure a peace with Cromwell; in which peace a secret article was introduced for the exclusion of the House of Orange. the war with England, after the Restoration, when it was thought expedient, on Opdam's defeat and death, that some of their own deputies should command the fleet, he was one of the three in commission, and wrote an accurate re

lation of all that happened during the expedition; for which, at his return, he received the solemn thanks of the States-General. In 1667 he established the perpetual edict for abolishing the office of Stadtholder, which produced seditions and tumults; on which the pensionary begged dismission from his post: this was granted, with thanks for his services. But the invasion of the French, and the internal division among the Hollanders, spread every where terror and confusion. Cornelius, the pensionary's brother, was imprisoned, and condemned to exile; and a report being raised that he would be rescued, the mob armed, and surrounded the prison where the two brothers were together, dragged them out, barbarously murdered them, hung the bodies on the gallows, and cut them to pieces. Such was the end of John De Witt, a man whose life had been devoted to the service of his country, without any consideration of his own emolument. Besides the work already mentioned, he wrote a book on the maxims of government, a translation of which, entitled, The true Interest and Political Maxims of the Republic of Holland, has been printed in London.

DE WITT'S LAND, part of the north-west coast of New Holland, discovered by a Dutch navigator of that name, in 1628. It is supposed to comprehend about ten degrees of latitude, and fifteen of longitude. Many low and sterile islands, were afterwards discovered along the coast, by the French.

body. The word is derived from the Greek, as mentioned in the preceding article.

DIADEM, in heraldry, is applied to circles or rims serving to inclose the crowns of sovereign princes, and to bear the globe and cross, or the fleurs-de-lis for their crest. The crowns of sovereigns are bound, some with a greater, and some with a less number of diadems. The bandage about the heads of Moors on shields is also called diadem, in blazoning. DI'ADROM, n. s. Aiaopoμew. The time in which any particular motion is performed.

A gry is one tenth of a line, a line one tenth of an inch, an inch one tenth of a philosophical foot, a philosophical foot one third of a pendulum; whose diadroms, in the latitude of forty-five degrees, are each equal to one second of time, or a sixtieth of a minute. Locke.

DIE'RESIS, n. s.

Διαίρεσις. The separation or disjunction of syllables, as aër. Diæresis is also a kind of metaplasm, or addition to a word, by dividing one syllable into two; as aulae, by a diæresis, is a word of three syllables, instead of aulæ. Dr. A. Rees.

DIERESIS, in medicine, is the consuming of the vessels of an animal body, when, from some corroding cause, certain passages are made which naturally ought not to have been, or certain natural passages are dilated beyond their ordinary dimensions, so that the humors which ought to have been contained in the vessels extravasate

or run out.

DIERESIS, in surgery, an operation serving to divide and separate the part when the continuity is a hindrance to the cure.

DIETETÆ, in Grecian antiquity, a kind of judges, of which there were two sorts; viz. Diætetæ cleroti, public arbitrators, chosen by lot to determine all causes exceeding ten drachms, within their own tribe; and from their sentence an appeal lay to the superior courts. And diætetæ diallecterii, private arbritators from whose sentence there lay no appeal. They always took an oath to administer justice without partiality.

DIAGLYPHICA, the art of cutting or engraving figures on metals, such as seals, intaglios, matrices of letters, &c., or coins for metals. See ENGRAVING.

DIAGNO'STICK, n. s. Alayivwoкw. A symptom by which a disease is distinguished. Used also figuratively.

One of our physicians proved disappointed of his prognosticks, or rather diagnosticks.

Harvey on Consumptions
DIAG'ONAL, adj. & n. s. Fr. diagonal,
DIAGONALLY, adv.
from Gr. dayw-

When a man has in his mind the idea of two lines, viz. the side and diagonal of a square, whereof the diagonal is an inch long, he may have the idea also of the division of that line into a certain number of equal parts. Locke.

All sorts of stone composed of granules, will cut and rive in any direction, as well in a perpendicular, or in a diagonal, as horizontally and parallel to the Woodward. side of the strata.

If a region of air be gradually removed from north to south, it would also blow diagonally between the north and east. Daricin.

DIAGONAL, in geometry, a right line drawn across a quadrilateral figure, from one angle to another; by some called the diameter, and by others the diametral, of the figure. See GEO

METRY.

DIAGORAS, surnamed the Atheist, lived in the ninety-first Olympiad. He was not a native of Athens, but he taught there. He had comhim. He sued the thief, who swore it was his posed a poem which a certain poet stole from own, and obtained fame by it. This tempted Diagoras to deny a Providence. The Athenians summoned him to give an account of his doctrine. He fled, and they set a price upon his head, promising a reward to any who should kill him; but he took shipping, and was

wrecked.

209

Strada tells us that the two friends, being each of them possessed of a magnetical needle, made a kind of dial-plate, inscribing it with the four-and-twenty letters, in the same manner as the hours of the day are marked upon the ordinary dial-plate.

Addison's Spectator. Scientifick dialists, by the geometrick considerations of lines, have found out rules to mark out the irregular motion of the shadow in all latitudes, and, on all planes.

Moxon.

While dial is derived from the Latin dies, day, because it indicates the hour of the day, the ancients also called it sciatherium, from its effect by the shadow.

1. DIALLING may be defined the art of drawing dials on the surface of any given body, whether plane or curved. By the Greeks and Romans this art is called gnomonica, and sciatherica, because it distinguishes the hours by the shadow of the gnomon.

2. This art is of great antiquity, for we read in Isaiah, xxxviii. 8, of the dial of Ahaz, who began to reign 400 years before Alexander, and within twelve years of the building of Rome.

3. Among the ancients Anaximenes the Milesian, and Thales, are said to have made dials; and Vitruvius mentions one made by the ancient Chaldee historian Berosus, on a reclining plane almost parallel to the equator.

4. Aristarchus of Samos invented the hemispherical dial, and there were at the same time some spherical ones, with a needle for a gnomon. The discus of Aristarchus was an horizontal dial, with its rim raised up all around to prevent the shadow from stretching too far.

5. It was late before the Romans became acquainted with dials. The first sun-dial at Rome was set up by Papirius Cursor, about the year of the city 460; before which time, says Pliny, there is no mention of any reckoning of time but by the sun's rising and setting: it was set up at or near the temple of Quirinus, but was very inaccurate. About thirty years after M. Valerius Messala, being consul, brought out of Sicily another dial, which he set up on a pillar near the rostrum; but because it was not made for that latitude it did not show the time truly. They made use of it for VOL. VII.

The

DEFINITIONS.

8. A dial is a surface, generally plane, upon which lines are described in such a manner, that the shadow of a wire, or of the upper edge of another plane, erected perpendicularly on the former, may show the time of the day.

9. The edge of the plane by which the time of the day is found is called the stile of the dial, which must be parallel to the earth's axis; and the line on which the said plane is erected is called the substile.

10. The angle included between the substile and stile is called the elevation, or height, of the stile.

11. Dials, the planes of which are parallel to the plane of the horizon, are called horizontal dials; and those which have their planes perpendicular to the plane of the horizon, are called vertical, or erect, dials.

12. Erect dials, the planes of which directly front the north or south, are called direct north, or south, dials: all other erect dials are called decliners, because their planes are turned away from the north or south.

13. Dials, the planes of which are neither parallel nor perpendicular to the plane of the horizon, are called inclining or reclining dials, according as their planes make acute or obtuse angies

P

with the horizon; and, if their planes are also turned aside from facing the south or north, they are called declining inclining, or declining reclining, dials.

14. The intersection of the plane of the dial, with that of the meridian, passing through the stile, is called the meridian of the dial, or the hour line of XII.

15. Meridians, the planes of which pass through the stile, and make angles of 15°, 30°, 45°, 60°, 75°, and 90°, with the meridian of the place, which marks the hour line of XII, are called hour circles; and their intersections with the plane of the dial are called hour lines.

16. In all declining dials the substile makes an angle with the hour line of XII., and this angle is called the distance of the substile from the meridian.

17. The declining plane's difference of longitude is the angle formed at the intersection of the stile and plane of the dial, by two meridians; one of which passes through the hour line of XII, and the other through the substile.

PRINCIPLES OF DIALLING.

18. If the whole earth, a Pe p, fig. 1, plate I., were transparent and hollow, like a sphere of glass, and had its equator divided into twenty-four equal parts by so many meridian semicircles, a, b, c, d, e, f, g, &c., one of which is the geographical meridian of any given place, as London, (which is supposed to be at the point a); and if the hour of XII were marked at the equator, both upon that meridian and the opposite one, and all the rest of the hours in order on the rest of the meridians, those meridians would be the hour circles of London: then, if the sphere had an opaque axis, as PEp, terminating in the poles P and p, the shadow of the axis would fall upon every particular meridian and hour when the sun came to the plane of the opposite meridian, and would consequently show the time at London, and at all other places on the meridian

of London.

19. If this sphere were cut through the middle by a solid plane, ABCD, in the rational horizon of London, one-half of the axis EP would be above the plane, and the other half below it; and, if straight lines were drawn from the centre of the plane to those points where its circumference is cut by the hour circles of the sphere, those lines would be the hour lines of a horizontal dial for London: for the shadow of the axis would fall upon each particular hour line of the dial when it fell upon the like hour circle of the sphere.

20. If the plane which cuts the sphere be upright, as AFCG, fig. 2. touching the given place (London) at F, and directly facing the meridian of London, it will then become the plane of an erect direct south dial; and if right lines be drawn, from its centre, E, to those points of its circumference where the hour circles of the sphere cut it, these will be the hour lines of a vertical or direct south dial for London, to which the hours are to be set, as in the figure, and the lower half, Ep, of the axis will cast a shadow on the hour of the day in this dial, at the same time that it would fall upon the like hour

circle of the sphere if the dial plane were hon zontal.

21. If the plane (still facing the meridian) be made to incline, or recline, any given number of degrees, the hour circles of the sphere will still cut the edge of the plane in those points to which the hour lines must be drawn straight from the centre; and the axis of the sphere will cast a shadow on these lines at the respective hours.

22. The same will be the case if the plane be made to decline by any given number of degrees from the meridian towards the east or west: provided the declination be less than 90°, or the reclination be less than the co-latitude of the place; and the axis of the sphere will be a gnomon, or stile, for the dial. But it cannot be a gnomon when the declination is quite 90°, nor when the reclination is equal to the colatitude; because, in these two cases, the axis has no elevation above the plane of the dial. And thus it appears that the plane of every dial represents the plane of some great circle upon the earth; and the gnomon the earth's axis, whether it be a fine wire, as in the above figures, or the edge of a thin plate, as in the common horizontal dials.

23. The whole earth, as to its bulk, is but a point, if compared to its distance from the sun; and therefore, if a small sphere of glass be placed upon any part of the earth's surface, so that its axis be parallel to the axis of the earth, and the sphere have such lines upon it, and such planes within it, as above described, it will show the hours of the day as truly as if it were placed at the earth's centre, and the shell of the earth were as transparent as glass.

24. But because it is impossible to have a hollow sphere of glass, perfectly true, blown round a solid plane; or, if it were, we could not get at the plane within the glass to set it in any given position; we make use of a wire sphere to explain the principles of dialling, by joining twenty-four semicircles together at the poles, and putting a thin flat plate of brass within it, as is shown in the preceding figures.

DIALLING BY THE TERRESTRIAL GLORE.

25. A common globe of twelve inches diameter has generally twenty-four meridian semicircles drawn upon it. If such a globe be elevated to the latitude of any given place, and turned about until one of these meridians cut the horizon in the north point, where the hour of XII is supposed to be marked, the rest of the meridians will cut the horizon at the respective distances of all the other hours from XII. And if these points of distance be marked on the horizon, and the globe be taken out of the horizon, and a flat board or plate be put into its place,even with the surface of the horizon; then if straight lines be drawn from the centre of the board, to those points of distance on the horizon which were cut by the semicircles; these lines will be the hour lines of a horizontal dial for that latitude, the edge of whose gnomon must be in the very same situation in which the axis of the globe was before it was taken out of the horizon: that is, the gnomon must make an angle with the plane of the dial,