177 



FORUM. 



FOUNDATIONS. 



178 



with an enclosed court before it and the prisons ; the Temple of Venus 

 and the Basilica ; and on the narrow side, opposite the Temple of 

 Jupiter, are three buildings generally considered to be the Curiae and 

 : on the east side is an enclosure, the use of which has not 



4/1 



Plan of the Forum at Pompeii. 



1,1, Curia j 2, .Erarinm ; 3, Chalciriicnm ; 4, Temple of Mercury ; 5, Senaculum ; 

 8, Pantheon ; 7, Temple of Jupiter; 8, Prison ; 9, Granary; 10, Temple 

 of Venus ; 11, Basilica. 



been determined, the Chalcidicum [CHALCIDICUM], the Temple of 

 Mercury, the Senaculum, and a building supposed to be a large eating- 

 house, generally known by the name of the Pantheon, in front of 

 which are the Tabernsc Argentaria:. The enclosed area of the forum 



Construction in wood and stone of the arjcostylc portico of the Forum. 

 a, holes for the joists of the upper door. 



was paved with Urge square pieces of marble, and the sides of the area 

 were adorned with statues. Opposite the curia! and a short way from 



ARTS A!D SCI. DIV. VOL. IV. 



them is a small triumphal arch. The forum was closed at night with 

 iron-barred gates, and it does not appear that chariots were admitted 

 into it, as the pavement of the streets terminates at the back of the 

 colonnade. The columns of the ambulatory are of the Greek Doric 

 order, and were being restored in the same style, though with better 

 materials, at the time the city was destroyed. The columns were 

 arseostyle, and the architraves were most probably of wood, as we may 

 infer from their being destroyed, while the frieze and cornice of stone 

 remain. 



FOUGASS, a small military mine, formed by sinking in the ground, 

 to a depth not exceeding 10 feet, a box of powder, or one containing 

 two or more loaded shells. The train of powder by which it is to be 

 fired is contained in a linen tube, and this is frequently protected by 

 being placed in a case of wood. A trench is cut in the ground to 

 receive the train, but it is subsequently filled up. 



Fougasses are sometimes employed in the defence of field forts, 

 and then they are formed under the glacis, or on the counterscarp, 

 at the points where the assault is expected : in this case generally 

 the train of powder is conveyed under ground to the counterscarp 

 of the ditch, where the fire is to be applied ; but occasionally this is 

 done in the interior of the work, the train being then made to pass 

 under the bottom of the ditch. 



Sometimes a fougass is used to destroy a small work, in which case 

 it is sunk withia the mass of the rampart or parapet. 



A stone fougass or rock mortar is formed by excavating a shaft in 

 the ground at an inclination of about 45, and about 6 feet deep. A 

 charge of powder of 50 or 60 Ibs. is placed at the bottom of this, with 

 a shield of wood 6 inches thick placed on it. The charge of stones is 

 then thrown in. There may be about 4 cubic yards of stone, each 

 stone or pebble not being less than half a pound in weight ; a 

 sufficient body of earth being placed vertically over the stones to make 

 them take effect in the right direction. The charge is fired as an 

 ordinary fougass. 



FOUNDATIONS. The surface which immediately supports a 

 building is technically known under the name of its foundation, whether 

 it be natural or artificial ; and from this function arise the laws appli- 

 cable to this particular branch of the arts of construction, namely, 

 that, howsoever formed, the foundations of a building must not be 

 susceptible of movement of any description whatever, after they shall 

 have assumed the statical condition they were designed to assume 

 when loaded to the fullest extent. It follows from the infinite varieties 

 of the resistances of the apparent portions of the earth's crust under 

 the various forces exercised by a building, that very great differences 

 must prevail in the modes of dealing with foundations ; and in addition 

 to the difficulties attending this part of the science, other, and perhaps 

 more serious ones arise from the circumstances under which the 

 foundations themselves may have to be prepared or executed. They 

 may, indeed, either be prepared in the open air, or under water, or 

 without disturbing to any serious extent the natural compressible sub- 

 soil ; and they may be either wholly or partially natural or artificial. 



Natural foundations require little description here. They exist 

 wherever the site upon which a building has to be erected is situated 

 upon a homogeneous formation of sufficient thickness to render any 

 lateral displacement of the bearing strata impossible. The only danger, 

 indeed, of this class of foundations would arise from the tendency to 

 such movement, and it therefore behoves the engineer or architect to 

 inquire very carefully into the conditions of substratification, and of 

 subterranean water-flow, which might be likely at any future time to 

 develope changes in the statical conditions of the surface strata. 

 Should there not exist any lower moveable beds, there are few rocks 

 which may not be unreservedly trusted as foundations. Gravels, 

 coarse sands, loams, and clays may equally be adopted, provided they 

 be not unconformably deposited on the edges of a highly inclined basin 

 of a rocky nature. Even soft alluvial deposits, when prevented from 

 spreading laterally, may at times be resorted to as natural foundations ; 

 but both in this case, and in the one in which diluvial formations 

 occur on the edge of highly inclined strata, care must be exercised in 

 the manner in which they are used. In fact, any stratum which will 

 support a vertical weight equal to 30 pounds upon the superficial inch 

 without sensible compression, after a month's trial, may be considered 

 fit to serve aa the foundation of a building : provided always that there 

 be no subjacent moveable strata. The lower courses or the footings of 

 the building itself must therefore present a bearing surface proportionate 

 to the resistance to compression likely to be met with in the natural 

 foundations. Even when the latter are distinctly susceptible of vertical 

 compression, there is, however, less danger from this cause than from 

 their tendency to lateral displacement, especially when they are of a 

 tolerably uniform character ; and it is for this reason that it is essential 

 to isolate the bearing surface of any important structure from any 

 irregular or permeable strata whose particles might be displaced by any 

 natural or artificial changes in the hydrographical conditions of the 

 locality. As very few natural foundations are to be met with whose 

 surfaces are sufficiently level to receive the footings of a building, it 

 has been customary of late years to fill in their depressions (to regu- 

 larise them, in short) by spreading a bed of concrete over them ; and 

 it may be received as a tolerably safe general rule, that every rock, 

 gravel, or clay formation will resist a vertical crushing weight which 

 may safely be brought upon the surface of the concrete itself. Of 



9 



