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Cataplasms take their name sometimes from the part to whichthey are applied, or effects they produce; and thus are calledwiacollemala, frontalia, epicarpia, epispastica, vesicatoria ; andwhi'n mustered is an ingredient, they are called sinapisms. Thesekind of applications are more easy than plasters or ointments.They are formed of some vegetable substances, and appliedof such a consistence as neither to adhere nor run : they are alsomore iiseuil when the intention is effected by the perpetuityof the heat or cold which they contain, for they retain themlonger than any other kind of composition. When designed torelax, or to promote suppuration, they should be applied warm.Their warmth, moisture, and the obstruction they give to perspi-ration, is the method of their answering that end. The pr.-perheal, when applied warm, is no more than to promote a kindlypleasant sensation ; for great heat prevents the design for w hienthey are used. They should be renewed as often as cool. Forrelaxating and suppurating, none excel the u'hile bread ] >oul ticmade of the crumb of an old loaf, a sufficient quantity ofmilk to boil the bread in, until it is soft, and a little oil ; whichlast ingredient, besides preventing the poultice from drying andsticking to the skin, also retains the heat longer than the breadand milk alone would do. To preserve the heat longer, thepoultice, when applied, may be covered with a strong ox’s blad-der. When designed to repel, they should be applied cold,and ought to he renewed as often as they become warm. Aproper composition for this end is a mixture of oatmeal andvinegar.

CATAPULTA , in antiquity, a military engine contrived forthe throwing of arrows, darts and stones upon the enemy. Someof these engines were of such force that they would throw stonesof 100 weight. Josephus takes notice ..f the surprising effects ofthese engines, and says, that the stones thrown out of them beatdown the battlements, knocked off the angles of the towers, andWould level a whole file of men from one end to the other, werethe phalanx ever so deep.

Catapulta , Batteting, is represented on Plate XU. Fig. 5.Phe base is. composed of two large beams, 2, 3. r Phe length ofthose beams is 13 diameters of the bore of the capitals, 9.At the two extremities of each beam, tw o double mortises areeut to receive the 8 tenons of two ero-s-heams, each of them 4of the diameters in length. In the centre of each of the beams°f the base, and near two-thirds of their length, a hole, perfectlyfound, and 16 inches in diameter, should be bored: theseholes must be exactly opposite to each other, and sin uki increasegradually to the inside of the beams, so that each of them, being16 inches on the outside towards the capitals, 9, should be 174 at

opening on the inside, and the edges carefully rounded otf.

the

The capitals, 9, are, in a manner, the soul of the machine, andSp rve to twist and strain the cordage, which forms its principle orpower of motion, 'lhe capitals are of cast brass or iron;-eachConsisting of a wheel with teeth, C 10, of 2-£ inches thick. Thehollow: or bore of these wheels should be 111 inches in diameter.Perfectly round, anil the edges smoothed down. As the frictionJJ'ftild be too great, if the capitals rubbed against the beams, byth exlrtJme straining of the cordage, which draws them toward-uese beams, that inconvenience is remedied by the means of- Wction wheels, or cylinders of brass, about the 13th of anc nct ' in diameter, and an inch and one-sixth in length, placedjttularly, and turning upon axes, as represented at D 13, B 12.;s n ? °i these friction-wheels at large with its screw, by which it, frstened into the beam, is represented at A. Upon this num-I r °* cylindrical wheels the capitals 9 must be placed in lheams, 2,3, so that the cylinders do not extend lo the teetli ol

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of wheels, which must receive a strong pinion 14. Bythis pinion, the wheel of the capital is made to

capital is

gaining the cordage with the key 15. 'Pile capital-wheel has at 0 ° n 8 catch 16, and another of the same kind may be addedV j J >r< -' l,t -’nt anything from giving way through the extreme andlri f 1 .’ 1 P°rce of the stiained cordage. 'Phe capital piece of theto j ( jV lle ‘s a nut or cross-pin of iron, 17, seen at C, and hammeredtwo mto ‘ ts form. It divides the hereof the capitals exactly inpj ec iual parts, and lixed in groves about an inch deep. 'Phisa s r e ’ <>r mil, ought to he about 2-j inches thick at the top 18,as Panted in the section at B ; and rounded off and polishedOf cmV as I >os si!)K*, that the cords folded over it may not be hurtby the roughness or edges of the iron. Its height ought

to be 8 inches, decreasing gradually in thickness to the bottom,where it ought to be only one inch. It must be very exactlyinserted in the capitals. After placing the two capitals in theholes of the two beams in a right line with each other, andfixing the two cross diametrical mils, or pieces over which thecordage is to wind, one end of the cord is reeved through ahole in one ol the capitals in the base, and made last to a nailwithin the beam. 'Phe other side of the cord is then carriedthrough the hole in the opposite beam and capital, and so wound,over the cross-pieces of iron in the centre of the two capitals,till they are lull, the cordage forming a large skain. Thetension of the cordage ought to be exactly equal, that is, theseveral foldings of the cold over the capital pieces should beequally strained, and so near each other, as not to leave theleast space between them. As soon as the first fold or skain ofcord has filled up one whole space or breadth of the capitalpieces, another must be earned over it; and so on, alwaysequally straining the end till no more will pass through the capi-tals, and the skain of cordage entirely tills them, observing torub it from time to time with soap. At 3 or 4 inches behindthe cordage, thus wound over the capital pieces, two very strongupright beams 21 are raised ; these are posts of oak 14 inchesthick, crossed over at top by another of the same solidity. Theheight of the upright beam is 7 \ diameters; each supportedbehind with very strong props 25, fixed at bottom in the ex-tremities of the base 2, 3. 'I he cross-beam 24 is supported inthe same manner by a prop in the centre. The tree, arm, orstylus 22, should be of sound ash. Its length is from 15 to 16 dia-meters of the bore of the capitals. The end of the bottom, orthat fixed in the middle of the skain, is 10 inches thick, and 14broad. To strengthen the arm or tree, it should be wrapped roundwith a cloth dipped in strong glue like the tree of a saddle, andbound very hard w ith waxed thread, of the sixth of an inch indiameter from the large end at bottom, almost to the top, as re-presented in the figure. At the top of the arm, just under theiron hand or receiver 27, a strong cord is fastened, with two loopstwisted one w ith in another, for the greater strength. Into thesetwo loops the hook of a brass pulley 2S is put. The cord 29 isthen reeved through the pulley, and fastened to the roll 30.l he cock or trigger 31, w hich serves‘as a stay, is then broughtto it, and made fast by its hook to the extremity of the hand.27, in which the body to be discharged is placed. The pulley atthe neck of the arm is then unhooked ; and when the trigger isto let it off, a stroke must be given upon it with an iron bar orcrow of about an inch in diameter; on which the arm flies upw ith a force almost equal to that of a modern mortar. Thecushion or stomacher, 23, placed exactly in the middle of thecross-beam 24, should be covered with a tanned ox hide, andstuffed with hair, the arm striking against it with inconceivableforce. It is to be observed, that the tree or arm, 22, describes anangle of 90 degrees, beginning at the cock, and ending at thestomacher or cu hion.

Catapulta for Arrows, Spears, or Darts. Some ofthe spears, Ac. thrown by these engines, are said to have been18 feet long. In Fig. 6, ABCD is the frame that holds the dartsor arrows, which may be of different numbers, and placed indifferent directions. EF is a large and strong iron spring, whichis bent by a rope that goes over three pullies, I, K, L; and isdrawn by one or several men ; this rope may be fastened to apin at M. The rope, therefore, being set at liberty, the springmust strike the darts with gr eat violence, and send them, withsurprising velocity, to a great distance. 'Ihis instrument differsin some particulars from the description we have of that of theancients ; principally in the throwing of several darts at the sametime, one only being thrown by theirs.

CATARACT, in hydrography, a fall of water

from on high; a shoot of water ; a cascade. Cataracts are occa-sioned by precipices in the channel of a liver, caused by rocksor other obstacles, stopping the course of the stream, fromwhence the water falls with a great noise and impetuosity. .Such are the cataracts of the. Nile, the Danube, Rhine , &c.

In that of Niagara, the perpendicular fall of the water is 137feet: and in that” of Pistill Rhaiadr, in North Wales , the fall ofwater is near 240 feet from the mountain to the lower pool.What we call a cataract, the ancients usually called catadupa.Ilemiinius has an express dissertation, “ De admitandis mundi

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