as the stress upon the chains, attains its minimum value. Dredging machines, mechanical contrivances placed in the hull of a vessel, and floated in situations for the dredging and clearing away of deposited matter from the beds of rivers, canals, harbours, basins, &c. Some machines for these purposes are to be compared to harrows or shovels, which loosen the deposit preparatory to its removal either by the action of the tide or stream; but for the more general purposes of dredging, vast improvements have been effected. The machinery of the best construction is described in Weale's Quarterly Papers on Engineering.'

Dressings, the mouldings and sculp

tured decorations of all kinds which are used on the walls and ceilings of a building for the purpose of ornament

Drift, a piece of hardened steel, notched at the sides and made slightly tapering: it is used for enlarging a hole in a piece of metal to a particular size by being driven through it

Drift, the horizontal force which an

arch exerts with a tendency to overset the piers from which it springs

Drifts, in the sheer draught, are where the rails are cut off and ended with a scroll. Pieces fitted to form the drifts are called driftpieces. Driftway, in mining, is a passage cut

under the earth from shaft to shaft Drill, a tool for cutting a circular hole in a piece of metal Drilling machine, a machine for cutting circular holes in metal by means of a revolving drill Drilling, the art of boring small holes. Drilling may be effected in a lathe. The drill is screwed upon the spindle, so that its point shall turn exactly opposite that of the screw in the shifting head. Various ingenious improvements have recently been made.

Drip, the projecting edge of a moulding channeled beneath, so that the rain will drip from it: the corona of the Italian architects Dripstone, called also the label,' 'weather moulding,' and 'water table,' a projecting tablet or moulding over the heads of doorways, windows, archways, niches, &c. Driver, the foremost spur in the bulge-ways, the heel of which is fayed to the foreside of the foremost poppet, and the sides placed to look fore and aft in a ship Driver, the bent piece of iron fixed in

the centre chuck, and projecting over it to meet the carrier, and drive it forward

Driving shaft, any shaft which gives motion to another shaft

Driving springs, the springs fixed upon the boxes of the driving axle of a locomotive engine, to support the weight and to deaden the shocks caused by irregularities in

the rails

Driving wheels, the large wheels of a locomotive engine, which are fixed upon the crank-axle, or main shaft of the engine

Drum, in architecture, the bell-formed part of the Corinthian and Composite capitals

Drum, a hollow cylinder fixed on a shaft, for driving another shaft by a band

Drummond light, a peculiar light invented by the late Capt. Drummond, called a heliostat, which reflected the sun's rays in sufficient abundance to render the station which was to be observed visible. This invention obviated the difficulty of distinguishing the stations chosen for the angular points of the triangles in a geodesical survey: where those stations are many miles asunder, it is necessary to have recourse to illuminations even in day-time.

Druxey, timber in a state of decay, with white spongy veins Dryness is a term by which artists express the common defect of the

early painters in oil, who had but little knowledge of the flowing contours which so elegantly show the delicate forms of the limbs and the insertion of the muscles; the flesh in their colouring appearing hard and stiff, instead of expressing a pleasing softness. The draperies of those early painters, and particularly of the Germans, concealed the limbs of the figures, without truth or elegance of choice; and even in their best masters, the draperies very frequently either demeaned or encumbered the figures. Dry-rot, a disease affecting timber,

and particularly the oak employed for naval purposes. Many contrivances are employed as remedies which have recently been patented, and have been successfully applied. Dub, to work with the adze Ductilimeter, an instrument for comparing the ductility of lead, tin, &c. Ductility is that property of bodies which admits of their being drawn out in length, while their diameter is diminished, without any actual fracture. Gold, silver, platinum, iron, copper, zinc, tin, lead, nickel, are ductile in the order here given : wire-drawing depends on ductility. Ductility, the property possessed by certain bodies of yielding to percussion, and receiving a change of form without breaking

Dums (in Cornish), frames of wood like the jambs of a door or the frame of a window; set in loose ground in adits and places that are weak and liable to fall in or tumble down Dungeon, a place of incarceration, formerly the principal tower or keep of a castle it was always the strongest and least accessible part of a building Durbar (Persian), a court or building where the sovereign or viceroy gives audience

Dutch Pink, English and Italian Pinks, are bright yellow colours used in distemper and for paperstaining, and other ordinary purposes. The pigment called 'stil,'

or 'stil de grain,' is a similar preparation, and a very fugitive yellow, the darker kind of which is called Brown Pink.

Dutch School of Painting. This school of art cannot be said to possess the perfections that are to be observed in the Flemish school; their subjects are derived from the tavern, the smith's shop, and from vulgar amusements of the rudest peasants. The expressions are sufficiently marked; but it is the expression of passions which debase, instead of ennobling human nature. It must be acknowledged, at the same time, that the Dutch painters have succeeded in several branches of the art. If they have chosen low subjects of imitation, they have represented them with great exactness; and truth must always please. If they have not succeeded in most difficult parts of the chiaro-oscuro, they at least excel in the most striking, such as in light confined in a narrow space, night illuminated by the moon, or by torches, and the light of a smith's forge. The Dutch understand the gradations of colours. They have no rivals in landscape painting, considered as the faithful representation of a particular scene; but they are far from equalling Titian, Poussin, Claude Lorraine, &c., who have carried to the greatest perfection the ideal landscape; and whose pictures, instead of being the topographical representation of certain places, are the combined result of every thing beautiful in imagination or in nature. Dyeing is the art of staining textile

substances with permanent colours Dyke, in coal mining, the banks of basalt or whin, by which the coal strata are frequently divided Dynamics, the science of moving powers, or of the action of forces on solid bodies when the result of that action is motion.

GENERAL DEFINITIONS.

1. The mass of a body is the quantity of matter of which it is

composed, and is proportional to its weight, or to the force which must be applied to the body to prevent its gravitating to the earth, and which, being greater or less as the mass is greater or less, we regard as a measure of the mass itself.

2. Density is a word by which we indicate the comparative closeness or otherwise of the particles of bodies, and is synonymous with the term specific gravity. Those bodies which have the greatest number of particles, or the greatest quantity of matter, in a given magnitude, we call most dense; those which have "the least quantity of matter, least dense. Thus lead is more dense than freestone; freestone more dense than oak; and oak more dense than cork.

3. The velocity with which a body in motion moves, is measured by the space over which it passes in any given time; the unit usually assumed being one second.

4. If the body passes over an equal space in each successive unit of time, the body is said to move uniformly, or to have a uniform velocity, and the measure of such velocity is the space actually passed over by the body in each second.

5. If, however, the body passes over a greater space in each successive second than it did in the preceding, then it is said to move with an accelerated velocity: when the differences between the spaces moved over in any two successive seconds is the same, at whatever period of the body's motion they be taken, or in other words, when the successive spaces form an arithmetical progression, the body is said to move with a uniformly accelerated velocity; but when the spaces passed over in successive seconds

EAR

Early English Architecture, the first of the pointed or Gothic styles of architecture used in England. It

increase according to any other law, the body is then said to have its velocity variably accelerated.

6. If, on the other hand, the body passes over a smaller space in each successive second than it did in the preceding, then it is said to move with a retarded velocity; which, if the successive spaces form a decreasing arithmetical series, is said to be uniformly retarded; if otherwise, it is said to be variably retarded.

7. The velocity of a body whose motion is variable is expressed at any moment by the space which it would pass over in a second, if its velocity at the moment spoken of were to continue uniform for that period.

8. Mechanical effect is measured by the product of the mass or weight of the body into the space over which it has been moved; no regard being had to the time occupied. The unit of mechanical effect is a weight of one pound raised through a space of one foot.

9. The momentum of a body in motion means the mechanical effect which such a body will produce in a moment (or second) of time, and varies as the weight of the body multiplied by its velocity.

10. The vis viva of a body in motion is the whole mechanical effect which it will produce in being brought to a state of rest, no regard being had to the time in which the effect is produced, and it varies as the weight of the body multiplied by the square of its velocity. Dynamometer, an instrument which

measures any thing to which the name of power has been given, whether that of an animal or otherwise

Dysodile, a papyraceous brown coal

EAR

immediately succeeded the Norman towards the end of the 12th century, and gradually merged into

128. per diem. The cost of the machine is £1500. Earth-work in England has generally been taken at 10d. to 1s. per yard.

This apparatus is a strong rectangular frame of wood, or other material, mounted upon wheels, supported, together with the machine, on a temporary railroad : at one end of this frame is a strong crane, consisting of a vertical shaft or pillar, with the jib supported by diagonal stays, or arms to the end of the chain tackle is suspended a scoop, shovel, or scraper, made of strong boiler-plate iron, and consisting of two sides, end, and bottom, the edge of which latter is provided with four or more projecting points or cutters; and between these, and at their roots, is a steel edge, well tempered, so as to resist stone or other hard subtance with which it may come in contact: the chain tackle is attached to the sides of the shovel, and passes over a pulley at the end of the jib, and over another pulley fixed on the top of the pillar or support of the crane, and from thence to the barrel, upon which it is made to coil: the periphery of the last-mentioned pulley is formed with indentations to receive the links of the chain, for the purpose of giving motion to the pulley, which has on its axis a bevelwheel, taking into and driving a similar wheel, upon the end of an inclined shaft, which shaft actuates certain machinery fixed to and supported by the diagonal arms of the crane. This machinery consists of a barrel, with other appurtenances, round which is passed a chain, with its ends attached the opposite ends of a beam or arm, which is also fixed to the shovel or scraper. The crane is capable of being moved round, so as to turn the scoop, when elevated, either to the right or left, in a horizontal direction: for this purpose a 'horse-shoe pulley,'

having a groove in its periphery, is affixed to the upper part of the crane a chain, attached at each end to a transverse bar, passes round this pulley, and over certain horizontal and vertical guide pulleys, to a barrel, in such a manner that, by reversing the motion of the barrel, the jib of the crane can be turned either to the right or left. A steam engine is erected at one end of the rectangular frame, or platform, for the purpose of giving motion to the various parts of the apparatus. When commencing operation, the shovel, or scraper, is suspended by the chain tackle in a nearly vertical position, with the steel points towards the ground by releasing the clicks, or catches, of the chain barrel, and applying the brake, the shovel will be lowered, and force itself, by its own weight, into the ground; then by communicating motion to the chain barrel, the tackle will be raised, and, by means of the indented grooved pulley, motion will be given to the shaft, which actuates the machinery on the diagonal arms, which in its turn will force forward the shovel into the ground. At the same time that this motion is going forward, the shovel, or scraper, is being raised or lifted up by the tackle, by which means the shovel has a double motion, a thrusting forward motion and a lifting motion. When the shovel has become filled, and attained its proper altitude, these motions stop; and the shovel being prevented from returning by the clicks, or catches, the other barrel is thrown into gear by means of a coupling or clutch-box, and the crane turned round so as to bring the shovel over the cart, or other place of deposit; and by certain arrangements it is turned up so as to empty itself; in which position it is again ready for another operation.

Easel, for painters, the frame on