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and consists of three petals; and its fruit is The Aranea diadema being one of the ao oblong unilocnlar pod, contracted in the largest of the common spiders, serves to exmiddle, and containing two oblong, obtuse, emplify some of the principal characters of and gibbous seeds. There is but one species, the genus in a clearer manner than most found in the Indies, a tree, stem herba- others. At the tip of the abdomen are ceous, hairy, procumbent. The branches placed five papillæ or teats, through which trail on the ground, and the germ, after the insect draws its thread; and as each of flowering, thrusts itself ander grozod, where these papillæ is furnished with a vast nunthe food is formed and ripened.
ber of foramina or outlets, disposed over its ARACHNOIDES, in zoology, a name whole surface, it follows that what we comgiven to those echini marini, or sen-hedge- monly term a spider's thread, is in reality hogs, which are of a circular form, but formed of a collection of a great many disvariously indented at the edges. See tinct ones; the animal possessing the power Echinus.
of drawing out more or fewer at pleasure; ARALIA, berry-beuring angelica, in bo- and if it should draw from all the foramina tany, a genus of the Pentandria Pentagynia at once, the thread might consist of many class of plants, the flowers of which are col- hundred distinct filaments. The eyes, which lected into an umbel, of a globose figure, are situated on the upper part or front of with a very small involucrum ; the perian- the thorax, are eight in number, placed at thium is very small, divided into five parts, a small distance from cach other, and havand placed on the germen ; the corolla con ing the appearance of the stemmiata in the sists of five, ovato-acute, sessile, reflex pe- generality of insects. The fangs or piercers, tals; the fruit is a roundish, coronated, with which the animal wounds its prey, are striated berry; having five cells; the seeds strong, curved, sharp-pointed, and each furare single, hard, and oblong. There are nished on the inside, near the tip, with a four divisions, viz. A. leaves entire; B. leaves small oblong hole or slit, through which is lobed; C. leaves in finger-like divisions; D. evacuated a poisonous fluid into the wound leaves decompound, and more than decom- made by the point itself, these organs operat. pound. In the first there are three species; ing in miniature on the same principle with in the second one; in the third two; and in the fangs in poisonous serpents. The feet the fourth four.
are of a highly curious structure; the two ARANEA, in natural history, the spider, claws with which each is terminated being a genus of insects of the order Aptera. Gen. furnished on its under side with several char. legs eight; eyes eight, sometimes six; parallel processes resembling the teeth of a mouth furnislied with two books, or holders ; comb, and enabling the animal to dispose feelers two, jointed, the tips of which in the and manage with the utmost facility the dismale distinguish the sex; abdomen terminat- position of the threads in its web, &c. ed by papillæ, or teats, through which the Aranea tarantula, or Tarantula spider, insect draws the thread.
of which so many idle recitals have been One of the largest of the European spi- detailed in the works of the learned, and ders is the Aranea diadema of Linnæus, wliich, even to this day, continues in which is extremely common in our own some countries to exercise the faith and country, and is chiefly seen during the au. ignorance of the volgar, is a native of the tumnal season in gardens, &c. The body warmer parts of Italy and other warm Eu. of this species, when full grown, is not much ropean regions, and is generally found in inferior in size to a small bazel nut: the ab- dry and sunny plains. It is the largest of all domen is beautifully marked by a longitudi- the European spiders, but the extraordináry nal series of round, or drop-shaped milk, symptoms supposed to ensue from the bite white spots, crossed by others of similar of this insect, as well as their supposed cure appearance, so as to represent, in some de- by the power of music alone, are entirely gree, the pattern of a small diadem. This fabulous, and are now sufficiently exploded spider, in the months of September and among all rational philosophers. The giganOctober, forms, in some convenient spot or tic Aranea avicularia, or Bird-catching shelter, a large round close, or thick web spider, is not uncommon in many parts of of yellow silk, in which it deposits its eggs, the East Indies and South America, where guarding the round web with a secondary it resides among trees ; frequently seizing one of a looser texture. The young are on small birds, which it destroys by woundhatched in the ensuing May, the parent in- ing with its fangs, and afterwards sucking sects dying towards the close of autumn.' their blood : during the early part of the
last century a project was entertained by gress; and when satisfied with their journey a French gentleman, Monsieur Bon of and their prey, they suffer themselves to Montpelier, of instituting a manufacture of fall, by contracting their limbs, and graspiders' silk, and the Royal Academy, to dually disengaging themselves from the which the scheme was proposed, appointed thread which supports them. See Plate I. the ingenious Reaumur to repeat the expe- Entomology, fig. 7 and 8. riments of Monsieur Bon, in order to as ARAUCARIA, in botany, a genus of the certain how far the proposed plan might Dioecia slonadelphia class and order. be carried; but, after making the proper Male, calyx scales of an ament, terminated trials, Mr. Reaumur found it to be imprac- by a leafet; no corol; antheræ 10 to 12, ticable, on account of the natural disposi- withont tilaments. Female, calyx an ament tion of these animals, which is such as will with many germs ; no corol; stigma twoby no means admit of their living peaceably valved, unequal ; seeds numerous, in a together in large numbers. Mr. Reaumur roundish cone. also computed that 663522 spiders would ARBITER, in civil law, a judge pomi. scarcely furnish a single pound of silk. Mon- nated by the magistrate, or chosen volun. sieur Bon, however, the first projector, car tarily by two parties, in order to decide ried his experiments so far as to obtain two their differences according to law. or three pair of stockings and gloves of this The civilians make this difference between silk; which were of an elegant grey colour, arbiter and arbitrator ; though both ground and were presented, as samples, to the their power on the compromise of the parRoyal Academy. It must be observed that ties, yet their liberty is different, for an arin this manufacture it is the silk of the egg- biter is to judge according to the usages of bags 'alone that can be used, being far the law, but the arbitrator is permitted to stronger than that of the webs. Monsieur use his own discretion, and accommodate Bon collected twelve or thirteen ounces of the difference in the manner that appears to these, and having caused them to be well him most just and equitable. cleared of dust, by properly beating with ARBITRATION, a power given by two sticks, he washed them perfectly clean in or more contending parties to some person warm water. After this they were laid to or persons to determine the dispute between steep, in a large vessel, with soap, salt. them: if the two do not agree it is usual to petre, and gum arabic. The whole was left add that another person be called as umpire, to boil over a gentle fire for three hours, to whose sole judgment it is then referred. and were afterwards again washed to get The submission to arbitration is the authoout the soap; then laid to dry for some rity given by the parties in controversy to days, after which they were carded, but the arbitrators, to determine and end their with much smaller cards than ordinary. The grievances; and this being a contract or silk is easily spun into a fine and strong agreement, must not be strictly taken, but thread : the difficulty being only to collect largely, according to the intent of the parthe silk-bags in sufficient quantity. There ties submitted. There are tive things inci, remains one more particularity in the history dent to an arbitration : 1. Matter of conof spiders, riz. the power of flight. It is troversy. 2. Submission. 3. Parties to the principally in the antumnal season that these submission. 4. Arbitrators. 5. Giving up diminutive adventurers ascend the air, and the arbitration. Matters relating to a freecontribute to fill it with that infinity of Aoat hold, debts due on band, and criminal ofing cobwebs which are so peculiarly conspi- fences are not to be arbitrated. cuons at that period of the year, When in ARBITRATOR, a private extraordinary clined to make these aerial excarsions, the judge, chosen by the mutual consent of parspider ascends some slight eminence, as the ties, to determine controversies between top of a wall, or the branch of a tree; and them. Arbitrators are to award what is turning itself with its head towards the equal between both parties, and the perwind, ejaculates several threads, and rising formance must be lawful and possible. An from its station, commits itself to the gale, action of debt may be bronght for money and is thus carried far beyond the height of adjudged to be paid by arbitrators. the loftiest towers, and enjoys the plea ARBOR Dianæ. See CHEMISTRY. sure of a clearer atmosphere. During their ARBOR vitæ. See Thuja. fight it is probable that spiders employ ARBOR, in mechanics, the principal part themselves in catching such minute winged of a machine which serves to sustain the insects as may happen to occur in their pro- rest; also the axis or spindle on which a
machine turns, as the arbor of a crane, Thus an arc is said to be of 30, 50, or 100 windmill, &c.
degrees, &c. · ARBUTUS, the straicberry-tree, in bo ARCH, in architecture, a concave buildtany, a genus of the Decandria Monogynią ing, with a mold bent in the form of a curve, class of plants, the calyx of which is a very erected to support some structure. Arches şmall, obtuse, permanent perianthium, divid are either circular, elliptical, or straight, as ed into five segments; the corolla consists they are improperly called by workmen. of a single oval petal, divided also into five Circular arches are also of three kinds ; 1. segments; the fruit is a roundish berry, con Semicircular, which have their centre in the taining five cells, and small osseous seeds. middle of a line drawn betwixt the feet of There are ten species.
the arch. 2. Scheme or skene, which are ARC concentric, is that which has the less than a semicircle, containing sonie same centre, with another arc.
90, and some 70 degrees. 3. Arches of the Arc diurnal, that part of a circle describ- third and fourth point, consisting of two ed by a heavenly body, between its rising arches of a circle meeting in an angle at the and setting; as the nocturnal are is that top, being drawn from the division of a described between its setting and rising: chord into three or more parts at pleasure. both these together are always equal.
Elliptical arches consist of a semi-ellipsis, ARcs equal, those which contain the same and have commonly a key-stone and imnumber of degrees, and whose radii are posts : they are usually described by work. equal.
men on three centres. ARCA, in conchology, a genus of Bi Straight arches are those used over doors valves, the animal of which is supposed to and windows, having plain straight edges, be a tethys, the valves are equal, and the both upper and under, which are parallel, hinge beset with numerous sharp teeth in but both the ends and joints point towards serted between each other.
a center. ARCA, in natural history, a genus of The term arch is peculiarly used for the worms of the order Testacea; animal a space between two piers of a bridge, intethys ; shell bivalve, equivalve; hinge with tended for the passage of water, vessels, &c. pumerous sharp teeth, alternately inserted ARCH of equilibration, is that which is between each other. There are, according in equilibrium in all its parts, having no to Gmelin, 43 species: but they are sepa
tendency to break in any one part more rated into four divisions, riz. A. margin very
than in another; and which is, therefore, entire, beaks recurved ; B. margin entire, safer and stronger than any other figure. beaks inflected; C, margin crenate, beaks No other arch than this can admit of a recurved; D. margin crenate, beaks inflect- horizontal line at top: it is of a form botla ed: of the latter we shall notice A. nucleus; graceful and convenient, as it may be made shell obliquely ovate, smoothish, with a higher or lower at pleasure, with the same triangular hinge; inhabits European seas, span. All other arches require extrados and is sometimes found fossile, the size of that are curved, more or less, either upa hazel nut, covered with an olivaceous wards or downwards ; of these, the elliptiskin, under which it is white, within silvery; cal arch approaches the nearest to that of shell unequally triangular, with very fine equilibration for strength and convenience, perpendicular striæ, crossed by a few arch and it is the best form for most bridges, as ed transverse ones; depression behind the it can be made of any height to the same beak, heart-shaped.
span, its haunches being at tiie same time ARCH, or Arc, in geometry, any part of sufficiently elevated above the water, even the circumference of a circle, or curved when it is very flat at top. Elliptical arches line, lying from one point to another, by also appear bolder and ligliter, are more which the quantity of the whole circle or uniformly strong, and are cheaper than line, or some other thing sought after, may most others, as they require less materials be gathered.
and labour. Of the other curves, the cyAll angles are measured by arcs. For cloidal arch is next in quality to the elliptithis parpose an arc is described having its
cal one, and lastly the circle. centre in the point or vertex of the angle: ARCHANGEL, in botany. See LA. and as every circle is supposed to be divided into 360°, an arc is estimated according ARCHES, or Court of ARCHES, the suto the number of degrees which it contains. preme court belonging to the Archbishop
of Canterbury, to which appeals Tie from weight; but it was afterwards discovered all the inferior courts within his province. or suspected that a part of the gold had
ARCHETYPE, the first model of a been stolen, and the like weight of silver work, which is copied after to make an substituted in its stead. Hiero, being angry other like it. Among minters it is used for at this imposition, desired Archimedes to the standard weight by which the others take it into consideration, how such a fraud are adjusted. The archetypal world, among might be certainly discovered. While enPlatonists, means the world as it existed gaged in the solution of this difficulty, he in the idea of God, before the visible cre- happened to go into the bath ; where obation.
serving that a quantity of water overflowed, ARCHIL. See LJCAEN.
equal to the bulk of his body, it presently ARCHIMEDES, in biography, one of occurred to bini, that Hiero's question the most celebrated mathematicians among might be answered by a like method ; upon the ancients, who flonrislied about 250 which he leaped out, and ran homeward, years before Christ, being about 50 years crying out suznice ! rugauce! I have found it tater than Euclid. He was born at Syra- out! I have found it out! He then made two cuse in Sicily, and was related to Hiero, masses, each of the same weight as the crown, who was then king of that city. The ma
one of gold and the other of silver ; this bethematical genius of Archimedes set him ing done, be filled a vessel to the brim with with such distinguished excellence in the water, and put the silver mass into it, upon view of the world, as rendered him both the which a quantity of water overflowed equal honour of his own age, and the admiration to the bulk of the mass ; then taking the of posterity. He was indeed the prince of mass of silver out he filled up the vessel the ancient mathematicians, being to them again, measuring the water exactly, which what Newton is to the moderns, to wliom
he put in ; this shewed him what measure in bis genius and character he bears a very
of water answered to a certain quantity of near resemblance. He was frequently lost
silver. Then he tried the gold in like manin a kind of reverie, so as to appear hardly
ner, and found that it caused a less quanti. sensible; he would study for days and ty of water to overflow, the gold being less nights together, neglecting his food; and
in bulk than the silver, though of the same, Plutarch tells us that be used to be carried weight. He then filled the vessel a third to the baths by force. Many particulars of time, and putting in the crown itself, he his life, and works, mathematical and me
found that it caused more water to overflow chanical, are recorded by several of the an than the golden mass of the same weight, cients, as Polybius, Livy, Plutarch, Pap- but less than the silver one; so that, findpus, &c. He was equally skilled in all the ing its bulk between the two masses of gold sciences, astronomy, geometry, mechanics, and silver, and that in certain known prohydrostatics, optics, &c. in all of which he portions, he was able to compute the real cxcelled, and made many and great inven- quantities of gold and silver in the crown, tions.
and so manitestly discovered the fraud. Archimedes, it is said, made a sphere of Archimedes also contrived many maglass, of a most surprising contrivance and chines for useful and beneficial purposes ; workmanship, exhibiting the motions of the among these, engines for launching large heavenly bocins in a very pleasing manner. ships ; screw pumps, for exhausting the
Many wonderful stories are told of his dis water out of ships, marshes or overflowed coveries, and of his very powerful and curi- lands, as Egypt, &c, which they would do ons machines, &c.
Hiero once admiring from any depth. them, Archimedes replied, these effects are But he became most famous by his cu. nothing, 66 but give me,” said he,
rions contrivances, by which the city of Syother place to fix a machine on, and I will racuse was so long defended, when be. move the earth.” He fell upon a eurious sieged by the Roman consul Marcellus ; device for discovering the deceit which showering upon the enemy sometimes long had been practised by a workman, employ- darts and stones of vast weight and in ed by the said king Hiero to make a golden great quantities; at other times lifting their crown. Hiero, having a mind to make an ships up into the air, that had come near offering to the gods of a golden crown, the walls, and dashing them to pieces by agrecd for one of great value, and weighed letting them fall down again; nor could ont the gold to the artificer. After some they find their sıfety in removing out of the ime he brought the crown home of the ful! reach of his cranes and levers, for there he
contrived to set fire to them with the rays leon, or engine to draw water out of places of the sun reflected from burning glasses. where it is stagnated, still in use under the
However, notwithstanding all his art, name of Archimedes's Screw. Athenæus, Syracuse was at length taken by storm, and speaking of the prodigious ship built by the Archimedes was so very intent npon some order of Hiero, says, that Archimedes ingeometrical problem, that he neither heard vented the cochleon, by means of which the the noise, nor regarded any thing else, till a hold, notwithstanding its depth, could be soldier that found him tracing lines, asked drained by one man. And Diodorus Sicubis name, and upon his request to be lus says, that he contrived this machine to gone, and not disorder his figures, slew drain Egypt, and that by a wonderful mehim. “ What gave Marcellus the greatest chanism it would exhaust the water from concern, says Plutarch, was the unhappy any depth.-3. The Helix, by means of fate of Archimedes, who was at that time in wich, Athenæus informs us, he launched his museum ; and his mind, as well as his Hiero's great ship. ~4. The Trispaston, eyes, so fixed and intent upon some geome- which, according to Tzetzes and Oribasius, trical figures, that he neither beard the ro.se could draw the most stupendous weights. and hurry of the Romans, nor perceiveri tiie 5. The Machines, which, according to Pocity to be taken. In this depth of study lybius, Livy, and Plutarch, he used in the and contemplation, a soldier came suddenly defence of Syracuse against Marcellus, conupon him, and commanded him to follow sisting of Tormenta, Balistæ, Catapults, Sahim to Marcellus; which he refusing to do, gittarii, Scorpions, Cranes, &c.—6. His till he had finished his problem, the soldier, Burning Glasses, with which he set fire to in a rage, drew his sword, and ran him the Roman gallies.-7. His Pneumatic through." Livy says he was slain by a sol- and Hydrostatic Engines, concerning which dier, not knowing who he was, while he was subjects he wrote some books, according to drawing schemes in the dust; that Marcel. Tzetzes, Pappus, and Tertullian.—8. His lus was grieved at his death, and took care of Sphere, which exhibited the celestial mohis funeral; and made his name a protection tions. And probably many others. and honour to those who could claim a rela A considerable volume might be written tionship to him. His death it seems hap- upon the curious methods and inventions of pened about the 142d or 143d Olympiad, or Archimedes, that appear in his mathematical 210 years before the birth of Christ,
writings now extant only. He was the first When Cicero was quæstor for Sicily, he who squared a curvilineal space ; unless discovered the tomb of Archimedes, all Hypocrates be excepted on account of overgrown with bushes and brambles ; which his lunes. In his time the conic sections be caused to be cleared, and the place set in were admitted into geometry, and he aporder. There were sphere and cylinder plied himself closely to the measuring of cut upon it, with an inscription, but the lat- them, as well as other figures. Accordingly ter part of the verses were quite worn out. he determined the relations of spheres,
Many of the works of this great man are spheroids, and conoids to cylinders and still extant, though the greatest parts of cones ; and the relations of parabolas to them are lost. The pieces remaining are as rectilineal planes whose quadratures had follow: 1. Two books on the Sphere and long before been determined by Euclid. He Cylinder.--2. The Dimension of the Circle, has left us also his attempts upon the circle : or Proportion between the Diameter and he proved that a circle is equal to a rightthe Circumference.—3. OT Spiral lines.-4. angled triangle, whose base is equal to the Of Conoids and Splieroids.-5. Of Equipon- circnmference, and its altitude equal to the derants, or Centres of Gravity.—6. The radius ; and consequently, that its area is Quadrature of the Parabola.—7. Of Bodies egnal to the rectangle of half the diameter floating on Fluids.—8. Lemmata.-9. Of and half the circumference ; thus reducing the Number of the Sand.
the quadrature of the circle to the determiAmong the works of Archimedes which nation of the ratio between the diameter are lost, may be reckoned the descriptions and circumference ; which determination of the following inventions, which may be however has never yet been done. Being gathered from himself and other ancient air. disappointed of the exact quadrature of the thors. 1. His Account of the Method which circle, for want of the rectification of its he employed to discover the Mixture of Gold circumference, which all bis methods would and Silver in the Crown, mentioned by Vi- not effect, he proceeded to assign an useful truyius.—2. His Description of the Coch- approximation to it: this he effected by the