The illustrated architectural, engineering, & mechanical drawing-book : for the use of schools, students, and artisans ; upwards of 300 illustrations (1856)
Burn, Robert Scott · London : Ward and Lock, 158 Fleet Street · leaf 110
fiir. 4. a (Z 6 the inside curve, called the softit, or intrados ; the key-stone is g. ENGINEERING, AND MECHANICAL DRAWING-BOOK. The exterior or upper curve of the arch is called the extrados/ 107
Architectural drawing · Mechanical drawing
Internet Archive · Public Domain Mark 1.0. Free to use for anything.
![An illustration from The gentlemens or builders companion : containing variety of usefull designs for doors, gateways, peers, pavilions, temples, chimney-pieces, slab tables, pier glasses, or tabernacle frames, ceiling peices [sic] &c. (1739)](https://img.insideoutlibrary.com/img/200/ia-gentlemensorbuil00jone-50-32.webp)