CARPENTRY. 



Continue- to fit any plane surface, whatever angle or angles the 



s, DI ai.y determinate line of the body, may make 



with tin- saul MII t;u -e ; as in purlin.., jack, i ;itu r&, &c. 



"" ~" ' Tln-M- pih.oples art' not only essential to carpentry, 



but .in- rijii .ily applicable to the constructive purls 



of masonry ; as in the formation of arches, bo a& to 



form their burfaces in the face of any wall, and to the 



BUI! >) given solid which bhall be a centre 



for the said arch. In plumbing, the sheets of lead 



for covering domes are formed by the rules for the 



covering of solids. 



Vaulting, 



and arch- 

 ing. 



VAULTING, GROININU, AND ARCHING. 



A simple vault is an interior concavity, extended 

 over two parallel opposite walls, or over all the dia- 

 metrically opposite sides or" one circular wall. 



The concavity, or interior surface of the vault, is 

 called the intrados. 



The intradoa of a simple vault is generally formed 

 of the portion of the surface of a cylinder, cylindroid, 

 or sphere, never greater than that of half the solid ; 

 and the springing lines of the coussinet, which termi- 

 uate the walls from which the vault rises, are gene- 

 rally straight lines, parallel to the axis of the cylinder 

 or cylindroid. 



When the vault is spherical, the circular wall ter- 

 minates in a level plane at top, f,-om which the vault 

 springs, and forms either a complete hemisphere, or 

 a portion of the sphere less than the hemisphere. 



Conical surfaces are seldom employed in vaulting, 

 but when a conical surface is employed for the intra- 

 dos of a vault, it should be semi-conic, with a hori- 

 zontal axis, or the surface of the whole cone with its 

 axi-^ vertical. 



All vaults which have a horizontal straight axis, 

 are called straight vaults. 



All vaults which have their axis horizontal, are 

 called horizonal vaults. 



A GROIN, is the excavation or hollow formed by 

 one simple vault piercing another at the same height, 

 such, that two geometrical solids being transversely 

 applied one after the other ; a portion of the groin 

 may have been in contact with the first solid, and the 

 remaining part in contact with the second solid, when 

 the first is removed. The most usual kind of groin- 

 ing is one cylinder piercing another, or a cylinder 

 or cylindroid piercing each other, having their axes 

 at right angles. 



A multangular groin, is that which is formed by 

 three or more simple vaults piercing each other at 

 the same height, so that if the several solids which 

 form each simple vault be respectively applied, only 

 one at a time, to succeeding portions of groined sur- 

 face, every portion of the groined surface will have 

 formed successive contact with certain corresponding 

 portions of each of the solids. 



A rectangular groin, is that which has the axes of 

 the simple vaults in two vertical planes, at right angles 

 to each other. 



An equi angular groin, is that in which the several 

 axes of the simple vaults form equal angles, around 

 the same point, in the same horizontal plane. 



The axis of each simple vault forming the intrados 

 of a groin, is the same with the axis of the geometri- 



cal solids, of which the intrados of the groin U com- 



When the breadths of the cross passage*, or open- 

 ingbof a groined vault, are equal, the groin u said to 

 , i 1 neral. 



A lit u ES are also formed by one simple vault pier* 

 cing another, after the same manner as groins. 



Arches have various names, according to the sur- 

 faces of the two geometrical bodies, which form the 

 simple vault. 



A cylindric arch, is that which is' formed by the 

 intersection of one portion of a cylinder with ano- 

 ther. 



A cylindroidic arch, is that which is formed by 

 the intersection of one portion of a cylinder with 

 another. 



A spheric arch, is that which is formed by the in- 

 tersection of one portion of the sphere with another. 



A conic arch, is that which is formed by the in- 

 tersection of one portion of a cone with another. 



The species of every arch, formed by the intersec- 

 tion of two vaults of unequal heights, is denoted by 

 two preceding words, the former of which ending in 

 o, indicates the simple vault, which has the greater 

 height, and the latter, ending in ic, indicates the 

 simple vault of the less height. 



When an arch is formed by the intersection of two 

 unequal cylindric vaults, it is called a cylindro- cylin- 

 dric arch. 



When an arch is formed by the intersection of a 

 cylindric vault with a spheric vault, and the spheric 

 portion being of greater height than the cylindric 

 portion, the arch is called a sphero-cylindric arch. 



When an arch is formed by the intersection of a 

 cylindric vault with a sphere vault, and the spheric 

 portion is of less altitude than the cylindric portion, 

 it is called a cylindro- spheric arch. 



When one conic vault pierces another of greater 

 altitude, the arch formed by the intersection is called 

 a cono-conic arch. 



History of Groins. 



The invention of groins must have been subsequent Hiitory of 

 to that of simple vaulting, and has probably origina- groin*, 

 ted from arched passages, when it was necessary to 

 occupy the whole height. At what time they were 

 first introduced in architecture is uncertain : the re- 

 mains of antiquity shew that they are of very remote 

 date, which, however, cannot be traced beyond the 

 times of Roman power and grandeur. Use or ne- 

 cessity was no doubt the occasion of their invention ; 

 but in process of time they were used as ornaments, 

 and became fashionable at the decline of the empire. 

 They are to be found in the amphitheatre at Rome, 

 formed at the intersections of the radiating and ellip- 

 tic passages. In the temple of Peace, and baths of 

 Dioclesian, at the same place, instead of massive piers, 

 they are s-upported upon columns, the most feeble of 

 all supports, and which would be incapable to resist 

 the lateral pressure of the arches, were it not for the 

 auxiliary support of the walls immediately behind 

 them at the sides and angles of the building. 



Groins continued to be used at the decline of the 

 Roman empire in ecclesiastic structures ; and where*. 



