BUILDING. 



suppose a wall 40 feel high, 2 feet thick ; 

 to have a sufficient foundation at 3 feet in 

 breadth, what, should be the breadth of 

 a foundation of a wall 60 feet high, 2$ feet 

 thick : by proportion it will be 40x2 

 : 3 :: 60 x2 : the ans. = Sfeet. This 



calculation will give the breadth of the 

 foundation of the required wall equal to 

 the breadth of the insisting wall itself; 

 when the height of the required wall is 

 equal to the ratio, which is the first term 

 40X2 = 80, divided by the second term 



on 



3, that is^J: = 26|. Thus a wall of 26| 



feet would have the breadth of its foun- 

 dation equal to its thickness above the 

 foundation, and less than 26| feet would 

 have a thinner foundation than even the 

 superstructure. But though the calcula- 

 tion in this case gives the foundation less 

 breadth than the thickness of its super- 

 structure, it must be considered, that it 

 only calculates the true breadth of sur- 

 face that should be opposed to the 

 ground, in order to prevent the wall from 

 penetration by its weight : though the 

 rule gives allthe breadth that is necessary, 

 on account of the weight of the insisting 

 wall, yet the breadth of the substructure 

 should always be greater than that of 

 the superstructure ; as it will stand more 

 firmly on its base when affected by later- 

 al pressure, and be less liable to rock by 

 the blowing of heavy winds. The least 

 breadth that is commonly given to the 

 substructure of stone walls is one foot 

 thicker than the superstructure. In 

 damp foundations, the superstructure 

 should always be separated from the sub- 

 structure by lead, tarred paper, or other 

 means. 



Stone Arch. Stone arch is a number of 

 stones so arranged,that, in consequence of 

 theirpressure upon one another and upon 

 their supports, they may be suspended 

 over a hollow space ; every interior stone 

 being such, that, if a plummet be depend- 

 ed by a line from any point in that stone, 

 the line will fall within the hollow space. 



Stone arches are generally hollow be- 

 low, and concave towards that hollow. 

 The interior stones ought to be truncated 

 wedges, and their faces, which form the 

 intrados, of less dimensions than the up- 

 per opposite surfaces which form the ex- 

 trados : so that when any stone endea- 

 vours to descend through the aperture 

 which surrounds it, it will be prevented 

 by the dimensions of the lower part of the 

 aperture being less than those of the top 

 of the stone which has to fall through it. 



Wedge-like stones forming an arch are 

 arch stones. 



The joints between the arch stones are 

 called sommerings. 



The support or supports of an arch are 

 called the reins of that arch. 



When the support or supports of an 

 arch are stone walls, the upper course or 

 courses, on which the beds of the ex- 

 treme arch stones rest, are called the 

 imposts. 



Spring course, or chaptrels of the arch, 

 are called the butments or abutments, or 

 spring beds, or skew backs of the arch. 



When an arch is either recessed in any 

 piece of masonry, or forms the head of 

 an aperture through that piece of mason- 

 ry, the arch stones, which are common to 

 the intrados and to the face of the mason- 

 ry, are called voussoirs, and the middle 

 voussoir is called the key-stone. 



Stone arches are used for a variety of 

 purposes, in supporting different parts of 

 a building, over apertures, when the 

 apertures are too wide for lintelling, and 

 over a wooden or stone lintel, to assist in 

 supporting the superincumbent build- 

 ing. 



Arches are also used to prop the sides 

 of a building-, and in soft foundations in- 

 verted arches are used, between narrow 

 piers, to prevent the pier from penetrat- 

 ing, by opposing a greater surface of re- 

 sistance to the ground. 



Floors and roofs are frequently sup- 

 ported with arches, in order to render 

 the building more secure from fire. 



Arches employed for several of these 

 purposes have been demoninated as fol- 

 lows : those over wooden lintels have 

 been called occult discharging arches, or 

 arches of discharge ; those used to prop 

 the sides of a building are called arch 

 boutants, or flying buttresses ; and those 

 over apertures, the intrados of which are 

 horizontal planes, have been absurdly 

 called straight arches ; it is only for the 

 property of its radiating joints this last is 

 called an arch. 



Because the courses in every kind of 

 masonry ought to be horizontal, or the 

 nearest position to it that the nature of 

 the arch will admit of, in stone arching, 

 it follows, that when the intrados is a ro- 

 tative figure, with a vertical axis, the 

 coursing joints will be conic surfaces, and 

 their intersections upon the intrados ho- 

 rizontal circles, and the transverse joints 

 will be planes tending to the axis : when 

 the axis is horizontal, the coursing joints 

 will be planes tending to the axis, and 

 the transverse joints will be either ver- 



