IRON ROOFS . 2 thick lines in these figures represent members in compression , and the thin lines members exposed to tension . When iron was first used in the construction of a roof it was only employed for those members of wooden trusses which were subject to tension , it being so much better…
![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)
