f material being , in some places more than others , attended with great increase in the cost of labour , and consequently a particular type that would be economica, ! in one situation , would be inexpedient in another . The primary characteristic or feature in the design of a roof is the main rib… … pressure upon the supports in a vertical direction only . Arches and other forms , m which the pressure is at an angle outwards with the vertical , giving to the roof what is generally called a horizontal thrust , will also be illustrated . Trusses may be best examined by comparing the bracing .…
![An illustration from Divina proportione : opera a tutti glingegni perspicaci e curiosi necessaria oue ciascun studioso di philosophia: prospettiua pictura sculptura: architectura: musica: e altre mathematice: suavissima: sotile: e admirabile doctrina consequira: e delecterassi: co[n] varie questione de secretissima scientia (1509)](https://img.insideoutlibrary.com/img/200/ia-divinaproportion00paci-188-404.webp)
![An illustration from Dess Circkelss vnd Richtscheyts, auch der Perspectiua, vnd Proportion der Menschen vnd Rosse, kurtze, doch gründtliche Vnderweisung, dess rechten gebrauchs : mit viel schönen Figuren, aller anfahenden Jugendt, vnnd andern liebhabern dieser Kunst, als Goldschmiden, Malern, Bildhauwern, Steinmetzen, Schreinern, [et]c. eigentlich fürgebildet, vormals im Truck nie gesehen, sonder jetzunder erstmals von neuwem an Tag gegeben (1618)](https://img.insideoutlibrary.com/img/200/ia-gri_33125010031561-68-0.webp)
