Chaf. XXII.

TIMBER DOMES.

1347

Fig 2169.

STIEKME’S SYSTEM FOR A DOMB.

In the example given of Stienne’s construction of a dome, we have a horizontal tie intro-duced above the curve, into which are framed two upright posts that form the sides of thelantern above : on the drum wall or cylinder that carries the timber dome two circularplates or curbs are first laid, generally formed of two thicknesses well bolted together :considering the dome to consist of four such trusses, as shown in the figure, they may beplaced to cross at right angles, each pair being parallel to the other, and situated at a dis-tance apart that suits the framing of the lantern.

The Church of the Salutation , at Venice , has a timber dome, the outer diameter of whichis 80 feet; it covers an interior brick hemispherical vault, which has an opening of nearly13 feet diameter. The exterior is formed of planks, in four thicknesses, laid oneover the other, united together by nails : ninety-six of these ribs, each about 6 inchesin thickness, have their lower ends let into a circular plate, formed of four thicknessesof plank, which lie over the attic cornice : at the top they are framed into a curb orplate which bears upon eight columns, placed round the opening of the brick dome : • thelantern and its balustrade externally is partly supported by this arrangement; eightadditional posts are introduced to carry the weight of the obelisks, which surround thebase of the lantern. To keep the ribs which form the outer dome from spreading, they arehooped round with iron at about one-third of their height, the hoop being 5 inches wide,

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