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The ancients, Salmafuis obferves, had only three kinds of 

 vaults : the firft, the fornix, made cradle-wife ; the fecond, 

 the tejlitudo, tortoife-wife, called by tlie French cul de four, 

 or oven-wife ; the third, the concha, made fhell-wife. 



But the moderns fubdivide thefe three forts into a great 

 many more, to which they give different names, accord- 

 ing to their figures and ufe ; fome are circular, others 

 elliptical. Sec. 



The fweeps of fome, again, are larger, and others Irfs 

 portions of a fphere : all above hemifpheres are caUed M^h, 

 or furmounteJ vdiults ; all that are lefs than hemifpheres, are 

 low, or furbafed Vciults, &c. 



In fome, the height is greater than the diameter ; in 

 others, it is lefs : there are others, again, quite flat, only 

 made with haunfes ; others oven-like, or in form of a cul de 

 four, &c. and others growing wider, as they lengthen, hke 

 a trumpet. 



Of vaults, fome are Jingle, others douhle, crofs, diagonal, 

 horizontal, afcending, defending, angular, oblique, pendent, &c. 

 There are hkewife Gothic vaults, with pendenli-ves, &c. 



Vaults, Majler, are thofe which cover the principal 

 parts of buildings ; in contradiftinftion to the lefs, or fu- 

 bordinate vaults, which only cover fome httle part, as a 

 paiTage, a gate, &c. 



Vault, Double, is fuch an one as, being built over another, 

 to make the exterior decoration range with the interior, leaves 

 a fpace between the convexity of the one and the concavity 

 of the other : as in the dome of St. Paul's at London, and 

 that of St. Peter's at Rome. 



Vaults ivith Compartiments, are fuch whofe fweep, or 

 inner face, is enriched with pannels of fculpture, feparated 

 by platbands ; thefe compartiments, which are of different 

 figures, according to the vaults, and are ufually gilt on a 

 white ground, are made with ftucco, on brick vaults ; as in 

 the church of St. Peter's at Rome ; and with plaiiler, on 

 timber vaults. 



Vaults, Theory of. A femicircular arch, or vault. Hand- 

 ing on two piedroits, or impofts, and all the ftones that com- 

 pofe it being cut and placed in fuch manner, as that their 

 joints, or beds, being prolonged, do all meet in the centre of 

 the vault ; it is evident, all the ftones muft be in form of 

 wedges, i. e. they muft be wider and bigger at top than at 

 bottom ; by virtue of which they fuftain each other, and 

 mutually oppofe the effort of their weight, which deter- 

 mines them to fall. 



The ftone in the middle of the vault, wliich is perpendi- 

 cular to the horizon, and is called the key of the vault, is 

 fuftained on each fide by the two contiguous ftones, juft 

 as by two inclined planes ; and of confequence, the effort 

 it makes to fall, is not equal to its weight. 



But ftill that effort is greater, as the inclined planes are 

 lefs inclined ; fo that if they were infinitely little inclined, 

 /'. e. if they were perpendicular to the horizon, as well as 

 the key, it would tend to fall with its whole weight, and 

 would aflually fall, but for the mortar. 



The fecond ftone, which is on the right or left of the 

 key-ftone, is fuftained by a third ; which, by virtue of the 

 figure of the vault, is neceffarily more inchned to the fe- 

 cond, than the fecond is to the firft ; and, of confequence, 

 the fecond, in the effort it makes to fall, employs a lefs 

 part of its weight than the firft. 



For the fame reafon, all the ftones, reckoning from the 

 key-ftone, employ ftill a lefs and lefs part of their weight 

 to the laft; which refting on an horizontal plane, cm- 

 ploys no part of its weight ; or, which is the fame thing, 

 makes no effort to fall ; as being entirely fupportcd by the 

 impoft. 



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V A U 



Now, in vaults, a great point to be aimed at is, that all 

 the feveral ftones make an equal effort in order to fall : to 

 effeft this, it is vifible, that as each (reckoning from the 

 key to the impoft) employs a IHll lefs and lefs part of its 

 whole weight ; the firft, for inftance, only employing one- 

 half ; the fecond, one-third; the third, one-fourth,°&c. ; 

 there is no other way to make thofe different parts equal, 

 but by a proportionable augmentation of the whole, i. e. the 

 fecond ftone muft be heavier than the firft ; the third, than 

 the fecond, &c. to the laft ; which fliould be vaftly heavier. 



M. de la Hire demonftrates what that proportion is, in 

 which the weights of the ftones of a femicircular arch muft 

 be increafed, to be in equihbrio, or to tend with equal 

 forces to fall ; which gives the firmeft difpofition a vault can 

 have. 



Before him, architefts had no certain rule to conduft 

 themfelves by ; but did all at random. Reckoning the 

 degrees of the quadrant of the circle from the key-ftone to 

 the impoft ; the extremity of each ftone will take up fo 

 much the greater arch, as it is farther from the key. 



M. de la Hire's rule is, to augment the weight of each 

 ftone above that of the key-ftone, as much as the tangent 

 of the arch of the ftone exceeds the tangent of the arch of 

 half the key. Now, the tangent of the laft ftone, of 

 neceffity, becomes infinite, and of confequence, its weight 

 Ihould be fo too ; but as infinity has no place in praftice, 

 the rule amounts to this, that the laft ftones be loaded as 

 much as poflible, that they may the better refift the effort 

 which the vault makes to feparatc them ; which is called 

 the Jhoot, or drift, of the vault. 



M. Parent has fince determined the curve, or figure, 

 which the extrados, or outfide of a vault, whofe intrados, or 

 infide, is fpherical, ought to have, that all the ftones may be 

 in equilibrio. See Arch. 



Vault, Key of a. See Key and Voussoir. 



Vault, Reins or Fillings-up of a, are the fides which fuf- 

 tain it. 



Vault, Pendentive of a. See Pendentive. 



Vault, Impojl of a, is the ftone on which the firft vouffoir, 

 or arch-ftone of the vault, is laid. See Imposts. 



Vault, in the Manege. To vault a horfe-ftioe, is to 

 forge it hollow, for horfes that have high and round foles ; 

 to the end that the Ihoe, thus hollowed or vaulted, may not 

 bear upon the fole that is higher than the hoof ; but after 

 all, this fort of ihoe fpoils the feet ; for the fole, being 

 tenderer than the ftioe, affumes the form of the ftioe, and 

 becomes every day rounder and rounder. In Mr. Solleyfel's 

 Complete Horfeman, may be feen the true method of flioe- 

 ing high and round foles. See Shoe and Shoeing. 



Vault, or Volte. See Volte. 



Vault, Going to the, a term ufed by fportfmen for a 

 hare's taking the ground like a coney, which Ihe fometimes 

 does. 



Vault, Le, in Geography, a town of France, in the de- 

 partment of the Yonne ; 3 miles W. of Avallon. 



VAULX, a town of France, in the department of the 

 Straits of Calais ; 4 miles N.E. of Bapaum. 



Vaulx Milieux, a town of .France, in the department of 

 the Ifere; 12 miles N.E. of Vienne. 



VAUNIA, in Ancient Geography, a town of Italy, be- 

 longing to the Bechuni. Ptolemy. 



VAUNING, in Mineralogy. See Van, Vaxning- 

 Shovel, and Tin. 



VAUNT, or Vant. See Van. 



V AVST-Lay, among Hunters, a fetting of hounds, or 

 beagles, in a readinefs where the chafe is to pafs ; and caft- 

 ing them oft" before the reft of the kennel come in. 



VAUQUE- 



