ARC 



ARC 



ccs is vaulted in the groined form ; and 

 it is remarkable that the groins are not 

 formed by the intradoes of the vaults in 

 the ch:'.pe!s, for the summits of the vaults 

 in these rise but a small distance above 

 the spring ngs of the middle groins. It 

 may also be remarked, that the piers be- 

 tween the chapels have small arcades, 

 the summits of which arc considerably 

 below the cylindrical intradoes of the 

 side vaults. This circumstance is not 

 peculiar to these buildings, as is to be 

 found in many others. This is to be seen 

 distinctly in the plates of the Temple of 

 Peace, by Desgodetz. The Romans em- 

 ployed annular vaults, as in the temple 

 of Bacchus ; and in this, as in the temple 

 of Peace, and the baths of Dioclesian, the 

 summits of the arcades supporting the 

 cylindric wall and dome of the central 

 apartments do not intersect the annular 

 intradoes, but the convex side of the cy- 

 lindric wall which supports this annular 

 intrados, and consequently do not form 

 groins. The intradoes of the Roman 

 domes are of a semicircular section, as 

 may be seen in the Pantheon, the temple 

 of Bacchus at Rome, the temple of Jupi- 

 ter, and vestibule of the palace of Diocle- 

 sian, at Spalatro, in Dalmatia, while the 

 vertical section of the extradoes through 

 the axis is a much less segment, as the 

 Pantheon at Rome, and the vestibule and 

 palace of Dioclesian, exhibit. We have 

 no instances among the Roman or Grecian 

 buildings of pendentives or spandrels 

 which are supported by four pillars, or 

 by quadrangular or polygonal walls, and 

 which support themselves on a spheric 

 dome or cylindrical wall. Pendentives ri- 

 sing from four pillars, and a dome from 

 the top of the pendentives, were first put 

 in practice, it is said, in the celebrated 

 church of Sancta Sophia at Constantino- 

 ple. 



In the rectangular buildings of the mid- 

 dle ages, quadrangular, equal pitched 

 groins were generally used ; and in cir- 

 cular buildings we have annular groins, 

 as in the Church of the Holy Sepulchre 

 at Cambridge, and Temple Church, Lon- 

 don. We have also mentioned those cu- 

 rious groins which are exhibited in the 

 ceilings of King's College Chapel, Cam- 

 bridge; St. George's Chapel, Windsor; 

 und King Henry the Seventh's Chapel, 

 Westminster, of modern invention. 



In the present day, every species of 

 vaulting, that were either used by the an- 

 cients or throughout the middle ages, are 

 employed, both for the sake of variety, 

 and for elegance. 



It does not appear that the ancients 

 were acquainted with cylindrical, unequal 

 pitched groins, at least by way of orna- 

 ment; this form is, however, very beauti- 

 ful, as the arcades above the passage 

 through the front of Somerset-House 

 clearly exhibit. 



ARCHYTAS, ofTarentum, in biogra- 

 phy, a celebrated mathematician, cosmo- 

 grapher, and Pythagorean philosopher, 

 of whom Horace says, 



Marie ac terrte, mimeroque caren- 



ti-f arente 

 Mcnsorem colabeiit, Jlrcltyta, 6fc. 



He flourished about four hundred years 

 before Christ, and was the master of Pla- 

 to, Eudoxus, and Philolaus. He gave a 

 method of finding two mean proportion- 

 als between two given lines, and thence 

 the duplication of the cube, by means of 

 the conic sections. His skill in mecha- 

 nics was such, that he was said to be the 

 inventor of the crane and the screw ; and 

 he made a wooden pigeon that could fly 

 about, when it was once set off' ; but it 

 could not rise again of itself, after it 

 rested. He wrote sev'erai works, though 

 none of them are now extant, particularly 

 a treatise n e pt TV Ilav?ss, De Universo, 

 cited by Simplicius in Arist. Categ. It 

 is said he invented the ten categories. 

 He acquired great reputation both in his 

 legislative and military capacity ; having 

 commanded an army seven times without 

 ever being defeated. He was at last ship- 

 wrecked, and drowned in the Adriatic sea. 



Archytas was distinguished through 

 life by modesty and self-command. He 

 maintained, that virtue was to be pursued 

 for its own sake in every condition of life ; 

 that all excess is inconsistent with virtue; 

 that the mind is more injured by prospe- 

 rity than by adversity ; that there is no 

 pestilence so pernicious to human happi- 

 ness as pleasure ; and that the love of it 

 is a disease destructive to the human 

 mind. 



ARCTIC, in astronomy, an epithet giv- 

 en to the north pole, and likewise to a cir- 

 cle of the sphere parallel to the equator, 

 and 23 degrees 30 minutes distant from 

 the north pole. 



ARC'HUM, the burdock, in botany, a 

 genus of the Sv ngenesiaPolygamiaEqua- 

 lis class of plants; the common calyx of 

 which is globose and imbricated ; the 

 compound flower is tabulated and uni- 

 form, with equal hermaphrodite corollulse: 

 the proper flower is monopetalous and 

 tubulousj with a slender and very long 



