-DERMESTES, a genus of coleopterous insects. There are thirty species of which the principal are;

1. The lardarius of an oblong form, and a dim-black colour, easily distinguishable by a light brown stripe, that runs transversely almost the anterior half of the elytra. Its larva is oblong, and destroys preparations of animals preserved in col jections, and even feeds upon the insects.

2. The domesticus varies in size and colour; some being found of a dark-brown, others lighter. This insect makes in wooden furniture those little round holes that reduce it to powder.

3. The violaceus is a beautiful little insect; its elytra being of a violet-blue colour, and the thorax covered with green hairs; the legs are black. The larva, as well as the perfect insect inhabits the bodies of dead animals.

4 The fuinatus is of a light-brown colour, except the eyes, which are black. The thorax is margined, and the insect has the whole carriage of a scarabæus.

5. The ferrugineus is the largest of the genus; its colour is a rusty iron, having many black spots upon the elytra, which give the insect a gloomy appearance.

DESCANT, in the old music, the art of composing in several parts Descant is threefold, viz. pain, figurative, and dou

ble.

DESCENSION, in astronomy, is either right or oblique. Right descension is an arch of the equinoctial, intercepted between the next equinoctial point and the intersection of the meridian, passing through the centre of the object, at its setting, in a right sphere. Oblique descension is an archofthe equinoctial intercepted between the next equinoctial point and the horizon, passing through the centre of the object, at its setting, in an oblique sphere. DESCENT, in general, is the tendency of a body from a higher to a lower place. Heavy bodies meeting with no resistance, descend with an uniformly accelerated

motion.

Laws of descent of bodies. 1st, Heavy bodies, in an unresisting medium, fall with an uniformly accelerated motion. For it is the nature of all constant and uniform forces, such as that of gravity, at the same distance from the centre of the earth, to generate or produce equal additions of velocity in equal times. So that if in one second of time there is produced one degree of velocity, in two seconds there will be two degrees, in three s: conds three degrees, and so on; the degree or quantity of velocity being proportional to the length

of the time.

2d. The space descended by an un'form gravity, in any time, is half the space that ught be uniformly described in the same um by the last velocity acquired at the en of that time, if uniformly continued. For as the velocity increases in an arithmetal progression, the whole space descended by the variable velocity will be equal to the space described with the iddle velocity uniformly continued for the same time; and this again will be only the space that would be with the half of the last velocity, also uniformly continued for the same time, because the last veloty is double the middle velocity, being duced in a double time.

d. The spaces descended by a uniform

gravity, in different times, are proportional to the squares of the times, or the squares of the velocities. For the whole space descended in any number of particles of. time. consists of the sums of all the parti cularspaces or velocities, which are in arithmetical progression; but the sum of such an arithmetical progression, beginning at 0, and having the last term and the number of terms the same in quantity, is equal to halt the square of the last term, or of the number of terms; therefore the whole sums are as the squares of the times or velocities.

From many experiments it has been found that a heavy body descends freely through 16 feet 1 inch, or 16 feet, in the first second of time; and consequently by theorem 2, the velocity gained at the end of 1 second, is 32 feet per second. Hence by the same, and theorem 3, the velocity gained in any other time is 3214, and the space descended is 162. So that, if t denote the velocity, and the space due to the time, and there be put g=16;

then is

4h, For any other constant force, instead of the perpendicular free descent by gravity, find by experiment, or other wise, the space descended in one second by that force, and substitute that instead of 16 for the value of g in these formule or, if the proportion of the force to that of gravity be known, let the value of g be altered in the same proportion, and the same formule will hold good.

5th, The time of the oblique descent down any chord of a circle, drawn from the upper or lower point of the circle, is equal to the perpen icular descent through the diameter of the circle. eth, The descent, or vibration, through all arcs of the same cycloid, are equal, whether great or small.

through unequal arcs of a circle, are un 7th, But the descent, or vibration, equal; the times being greater in the greater arcs, and less in the less.

DESCENT, line of swiftest, is that which a body, falling by the action of gravity, de scribes in the shortest time possible, from une given point to another. And this line, is the arc of a cyclid, when the one point is not perpendicularly over the other.

DESCENT, in law, is the title by which a man on the death of his ancestor acquires his estate by right of representation as his heir at law; and an estate so des scending to the heir is in law called the

inheritance.

DESCENT, in heraldry, is used to express the coming down of any thing as, a lion en descent, is a lion with his head towards the base points and his heels to wards one of the corners of the chief, as

if it were leaping down from some high place.

DESCENTS, in fortification, are the holes, vaults, and hollow places, made by undermining the ground."

DESACH in heraldry, is when a beast has its limbs separated from its body, so that they still remain on the escutcheon, with a small separation from their natural places.

DESIGN, in a general sense, is the plan, representation or construction of a building, book, painting, &c.

In building the term ichnography may be used, when by design is only meant the plan of a building, or a flat figure drawn on paper: when some side or face of the building is raised from the ground, we may use the term orthography; and when buth front and sides are seen in perspective, it may be termed scenography. Dega, in manufactories, expresses the figures with which the workman enriches his stuff, or silk, and which he copies after some pain er, or draughtsman, as in diaper, tapestry. &c.

In undertaking such kinds of figured Ruffs it is necessary, that before the first stroke of the shuttle, the whole design be represented on the threads of the warp; we do not mean in colours, but with a number of little packthreads, which being disposed so as to raise the threads of the warp, letthe workmen see, from time to time, what kind of silk is to be put in the eve of the shuttle, for wouf. This method of preparing the work is called reading the design and reading the figure, which is performed in the following manner: A paper is provided, considerably broader thin the stuff, and of a length proportienate to what is intended to be represented on it. This they divide lengthwise, by as many blac lines as there are intended threads in the warp; and cross these lines, by others drawn breadthwise, which with the former, make little equal squares; on the paper thus squared, the draughtsman des gas his figures, and heightens them with colours as he sees fit for the direction of the workman.

DESIGN is used, in painting, for the first idea of a large work, drawn roughly; it also denotes the simple contour or outline of the figures intended to be repre seated, which design is sometimes drawn in crayons, or ink without any shadows. Sometimes it is etched; that is the shadows are expressed by sensible outlines, usually drawn across each other with the pen, crayon, or graver. Sometimes, again, the shadows are done with the crayon rubbed so as that there do not appear any lines: at other times, the grains or strokes of the crayon appear, as not being rubbed; sometimes the design is washed, that is, the shadows are done with a penelin Indian ink, or some other liquor; and sometimes colours are laid on like those intended for the grand work.

DETACHED PIECES, in fortification, are outworks detached or at a distance from the body of the place, as demilunes, ravelines, bastions, &c. In painting,the figures are said to be well detached, when they stand free and disengaged from each

gt er.

DETACHMENT, in military affairs, a

certain number ofsoldiers drawn out from several regiments or companies equally, to be employed as the general thinks proper; whether on an attack, at a siege, or in parties to scour the country.

DETENTS, in clock work, are those stops, which by being lifted up or let down, lock or unlock the clock in striking.

DETENT-WHEEL, or hoop-wheel, in a clock, that wheel which has a hoop almost round it, in which there is a vacancy at which the clock locks.

DETERGENTS, in pharmacy, are ad. hesive and softening medicines, and such as have a disposition to cleanse or carry off foul particles in their passage.

DETERMINATE PROBLEM, in geometry, that which has a limited number of answers: as the following, viz. To describe an isoceles triangle on a given line, whose angles at the base shall be double that at the vortex. But the following has two solutions, viz. To find an isoceles triangle, whose area and perimeter are given.

DETINUE, in law, is a writ which lies where any man comes to goods or chattels either by delivery or by finding, and refuses to give them up; and it lies for the detaining, when the detaining was unlawful.

DETONATION, in chemistry, the noise and explosion which any substance maks upon the application of fire. It is also called fulmination.

DETRANCHE',in heraldry, aline bendwise, proceeding from the dexter side but not from the very angle, diagonally athwart the shield.

DEVASTAVIT, in law, is a writ which lies against executors, to oblige them to pay debts for simple con ract, before debts on bonds, and specialties, or the like.

DEVISE, or device, in heraldry,painting, and sculpture, any emblem used to re present a cerian family, person, action, or quality with a suitable motto applied in a figurative sense.

DEVISE, in law, the act whereby a per son bequeaths his lands or tenements to another, by his last will and testament. the person who makes this act, is called the devisor, and he in whose favour the act is made,is termed the devisee.

DEVOURING, in heraldry, is when fishes are borne in an escutcheon in a feeding posture, for they swallow all the meat whole.

DEW, a dense mois vapour, falling on the earth in the form of a 'misling rain.

DEXTER, in heraldry, an appellation given to whatever belongs to the right side of the shield, or coat of aims: thus we say, bend-dexter, dexter-point, &c.

DIABETES, in physic, an excessive discharge of urine, which comes away crude, and exceeds the quantity of liquids drank.

DIACAUSTIC CURVE, a species of the caustic curves formed by refraction.

DIACHYLON, in pharmacy, an emol lient digestive plaster.

DIADELPHIA, in the Linnæan system of botany, a class of plants,the seventeenth in order; comprehending all those with papilionaceous and hermaphrodite flowers, and leguminous-eed-vessels.

DIADEM,inheraldry,is appliedto circles

hour-line of 12), are called hour-circles and their intersections with the plane the dial, are called hour-lines.

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.

The declining plane's difference of lon

DIAGNOSTIC, in medicine, a term given to those signs which indicate the present state of a disease, its nature and

cause.

DIAGONAL, in geometry, a right line drawn across a quadrilateral figure, from one angle to another, by some called the diameter. It is demonstrable, 1. That every diagonal divides a parallelogram into two equal parts. 2. That two diagonals drawn in any parallelogram bisect each other. 3. A line passing through the middle point of the diagonal of a parallelogram, divides the figure into two equal parts. 4. That the diagonal of a square is incommensurable with one of its sides. 5. That the sum of the squares of the diagonals of every parallelogram is equal to the sum of the squares of the four sides.

DIAGRAM, in geometry, a scheme for explaining and demonstrating the properties of a figure, whether triangle, square, circle, &c.

DIAL, or sun-dial, is a plane, upon which lines are described so that the shadow of a wire, or of the upper edge of a plate stile, erected perpendicularly on te plane may shew the truc time of the day The edge of the plate by which this is found, is called the stile, which must bearallel to the earth's axis; and the line on which this plate is erected, is called the substile. The angle included between the substile and stile, is called the elevation, or height of the stile.

Those dials whose planes are parallel to the plane of the horizon, are called horizontal dials; and those dia's whose planes are perpendicular to the plane of the horizon, vertical or erect dials.

Erect dials, whose planes front the north or south, are called erect north or south dials; and all other erect dials are called decliners, because their planes are turned from the north or south.

These dials, whose planes are neither parallel nor perpendicular to the plane of the horizon, are called inclining or rechining dials, as their planes make acute or obluse angles 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.

The intersection of the plane of the dia, with that of the mendian.passing through the stile, iscalled the meridian of the dial, o. the hour-lin. of XI

Those meridians, whose planes pass through the stile, and make a gles of 15. 30, 45, 60, 76, and 9 degrees with the meridian of the place (which marks the

section of the stile and pane of the dial, by two meridians, one of which passes through the hour-line of XII, and the other through the substile.

We shall now proceed to explain the different principles of their construction. If the whole earth a Pcp (Plate fig. 1) were transparent and hollow, like a glass sphere, and had its equator divided into twenty-four equal parts by so many meri. dian semi-circles, a, b, c, d, e, f, 8. &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 hours of XII were marked at the equator, upon that meridian and the opposte 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 opake axis, as P Ep, terminating in the poles P and A, 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 conse quently shew the time at London, and at all other places on that meridian.

Horizontal dial.-If this sphere was cut through the middle by a solid plane AB CD, 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 to those points where its circumference is cut by the hour-circles of the sphere, those lines would be the hourlines of a horizontal dial for London, for the shadow of the axis would fall upon each particular bour-line of the dial, when it fell upon the like hour-ircle of the sphere.

Vertical dials-If the plane which cuts the sphere be upright, as A FCG (fr. 9, touching the given plice at F, and directly facing the meridian of London, it will thes 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, cut by the hour-circles of the sphere, these will be the hou lines of a vertical or direct south d'al (or London, to which the bours are to be set as in the figure; and the lower half + p of the axis w I cast a shadow on the hour of the day in this dial, at the same time that it would fallupen the like hour-circle of the sphere, if the dial-plane was not in the way.

Inchining and reclining dials-If the plane be made to inenne, or recline, by a given number of degrees, the hour-arties of the sphere will still cut the edge of like plane in those points to which he Ourfines must be drawn straight from the centre; and the axis of the sphere will cita shadow on these ines at ine respec

hours. And it will be the same if the plane be made to decline by any given number of degrees from the meridian