Bond and .1Iasonry of Stone: bonding ashlars, which are larger and heavier than bricks, mortar becomes of minor importance; in fact, it may be dispensed with. Where the joints are closely fitted, it is usual simply to pour in milk of lime or thin cement mortar. Considering the greater weight of the stones, it is unnecessary to adhere strictly to the rules above given for bonding. Figure 5 represents a wall of ashlars of alternately high and low courses; Figure 6, one in which the ashlars are used only as a facing for a wall built of other mate rial; and in Figures 7 and 8 are shown walls in which such stone facing, is desired on one side only—in the former, alternate high and low courses, and in the latter, courses of equal height.
As a rule, the ashlars are quadrate in section and have a length, in the case of very dense stone (such as granite), equal to five times, and in solid stone (as marble) to four times, the height; in stone of medinin strength (like sandstone) to three times, and in less substantial stone not more than double, the height. When the ashlars form a facing only, then, as with the Gothic bond, there must be usQ•cl with cut stone as many headers (bind ing stones) as possible. The treatment of ashlar work on the exterior varies greatly, depending on the character of the building or of the parts to which it is applied. If the effect of strength is to be given, " bossage" or rustic work (fig. 9) is used, as in the parterre of the Dresden Museum. A similar result is obtained by bevelling the outer surfaces; sometimes also ornamental ashlars are employed. A fine example of ashlar work is the entrance to Austin Hall, Harvard University (.,6/. 2, fig. 2).
illasomy of 46.proximately Regular Stone. of approximately regular stone masonry are to be found in remains of constructions by the Pelasgian races, the " Cyclopean " or polygonal walls (fi/. I, fig. 12). The huge stones of this masonry were carefully joined without mortar. Respect ing the joining of walls made of irregular stones, it will only be necessary to say that attention must chiefly be paid to evenness of courses and hori zontal bedding of stones, no systematic alternation of joints being possible in this case.
Stone Framework differs from masonry in not dealing with the disposi tion of masses, but rather with the erection of framework made of single or beam-like parts (posts or pillars, lintels). The finest example of this construction is seen in the Greek temple (fig. TT), in which the cover ing by stone beams (architraves) of the spaces left between supports or columns is especially remarkable, in so far as in this form of covering- the side-thrust present in vaulted coverings is entirely absent. As the porti
cos of their temples show, the Greeks uscd this system also for the cover ing in of spaces, hollow pieces (lacnnaria) being set between the stones and beams placed at fixed intervals. The employing of stone framework, and especially the covering of spaces with stone beams, will always be limited in modern buildings, since, on account of their inferior tensile strength, stone beams cannot, like wooden or iron beams, be permitted to stand free over large spaces. Where arches or walls are set between the bays of stone frames, the case is quite different. These arches or walls are then the real, the pillars being only apparent, supports.
"wilted (arches) are used over openings in walls as well as over entire rooms (vaults proper). Every vaulting may be regarded as a pendent wall in which the sustaining of the individual parts (arch-stones or voussoirs) is effected in such a manner that by properly forming and placing these stones (g-enerally wedge-shaped) in position the pressure of those above, or any additional weight, is transferred from each stone to its neighbor obliquely downward upon the side walls (abutments); these must be of sufficient strength to carry the weight of the entire vaulting. The advantage of vaulting is that, unlike the case of the free-lving stone beams, it is not a question of resistance to bending, but of resistance to pressure, and consequently, regarding the width of span, the builder is not so strictly limited. It was formerly supposed that the ancient Greeks were not familiar with the arch, but the fact that there have been found remains of vaultings constructed by that people justifies the conclusion that they rather disdained the use of this architectural expedient. On the west coast of Northern Greece there is an old arch (fii. t, fig. 12) which, built with out mortar, lias a span of 143/1 feet.
Different names are applied to arcliesrpartly derived from the form of the arch-line—that is to say, the inner boundary-line of the arch-stones (voussoirs)—and partly from the general form and arrangement. The arch line may be a semicircle (as in Figure 12), a segment arch, an elliptical arch, a pointed or Gothic arch, etc., or even a straight line (flat or straight arch). According to their general form, these structures may be classified as cylindrical, groined, coved, spherical, and fan vaults.