SOFFITS, the under sides of the heads of apertures, or the parts of mouldings which may be projected upon a hori zontal plane, by lines perpendicular from all points of the mouldings upon that plane. Several methods have already been described, under the article ENVELOPE. What is proposed under the present head, is to show the methods adopted by early writers, not with a view of exposing their errors, but in order to guard the student against erroneous principles.
Figure 1, No. 1 and 2, as also Figure 2, No. 1 and 2, are from Swan's British Architect, Plate I.—" Figure I shows the opening of a window in a straight wall : draw the lines, ranging with the splay of the jambs; where these meet, s at a, is the length of the radius for drawing the curvature of the soffit ; then take the distance a b, transfer it from c to d, in Figure 2 ; then set your compasses in c, and draw the circular line e d; then set on the width of your soffit, and draw the external line ; this, when bent to a semicircle, will range along with each part of the straight wall.
"Figure 2 represents the opening of a window, of the same width as the former, in a circular wall. The shadowed semicircle above (Figure 2, No. 1) shows the opening of the arch. The arch-line may be divided into any number of parts, as here, into twelve. Draw lines perpendicular from the base-line, through all these divisions of the line h; then, in Figure 2, No. 2, draw a circular line, as for a straight wall ; and divide it into tho same number of parts as the arch-line above Figure 2; then take the distances from the line h to the circular wall. and set them from the outside line in Figure 2, Nu. 2, as at I, 2, 3, &c. to 12; then you will have the true curvature of your soffit, which, when bent to a semicircle, will, in every part, agree with a circu lar wall." The following are from the Carpenters' and Joiners' Re. pository, by William fain: " Figure 3 is a circular soffit in Hewing jambs. Draw the flowing of the jambs, e d and e f, to meet at the point a; then draw the arch d I: and divide the said arch into any number of equal parts, the more the truer the work, and run these parts on the dotted arch-line figure; then draw a line from a to g, which is the soffit stretched out ; then draw a dotted line from the centre, a, the parts of the arch-line, stretched out flir enough to receive the parts taken from the chord-line to the inside of the wall, and set them on the soffit, stretched out, as 1, 2, 3, 4, 5, 6, 7, S, and so on ; which will give the edge of the soffit.
Figure 5.-A is a circular soffit in a circular wall, which is flewing on the jambs, and square at top ; which makes the soffit winding as well as flewing. Draw the flowing of the jambs till they meet at o. The outside-arch is a semicircle, the inside-arch a semi-ellipsis. On the transverse diameter draw the plan of the wall, and the chord-line e d, equal to the opening on the inside 1 then, on the chord-line, e d, draw the semicircle, whose diameter is equal to e d; then, on the same chord-line, draw the lesser semicircle to the outside opening ; then draw the ellipsis, e d, whose height is exactly equal to the height of the lesser semicircle ; then divide the greater semicircle into a number of equal parts, and draw dotted lines from these parts to the inside curve of the wall ; then apply a rule from the point o, to where those lines meet the inside of the wall, and draw the black lines across the plan of the wall, which will give the width of the soffit at those places; then draw, with the centre o, the two arch-lines 1 b, f g, and on the arch 1 b, run the parts on the great circle ; and, from the centre, o, to these parts, draw the black lines across the soffit, stretched out, as 1, 3, 5, 7, 9; then take off the parts between the great semicircle and the ellipsis,and set them on the lines drawn across the soffit, stretched out, as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and trace through these points, which will give the inside of the soffit; then take the width of the plan on those black lines, and set it on the soffit, stretched out, will give the line g i f, which is the width of the soffit."
The following are taken from the British Palladio : " Figure 4 is a circular flewing soffit, in a circular wall : continue the flewing of the jambs, till they meet at e; then take the radius, e o, and draw the b o; then divide the greater and lesser arch into the same number of parts, as here into 8; this will do for a straight wall : as this plan flews circular, take half the distance of the chord-line of the lesser arch in the compasses, and strike the dotted arch which divide into four parts ; then set them on the chord-line of b o, as 1, 2, 3, 4, and draw lines from them to the arch line stretched out parallel to el; then take d g, the distance of the chord-line of the plan and the curve, and set it from it to n, on the line k e; then set the distances, 2, 3, 4, of the chord-line and curve-line, and set from the arch-line stretched out on the parallel lines, 2, 3, 4; trace through those points from b to a, and you have half the edge of the soffit. To get the breadth, make a section of the arch, as on the right of Figure 4, No. 1 ; draw the perpendicular lines, 1 5, 1 5, the distances of nto on the plan ; then take the distances o, 2, 3, 4, set them on the perpendicular line to the right, as marked from 1 to 2, 3, 4, 5, at right angles, the distances from the chord-line of the great arch, 1 1, 2 2, 3 3, 4 4, trace through them, and you have one side of this section ; for the smaller arch, proceed as before, and on the other perpendicular line, 5 1, of the distances, as figured, 5, 4, 3, 2, 0 ; from 0 to 1 draw the flewing line of the arch, at the crown ; take that distance, and set it from to k on the soffit ; also, to the perpendicular line on the side of the plan, an, a, set the com passes in na, and strike out the side of the flew to ; divide the difference of the line 0 1, from the section to a, into as many parts as the great arch ; then set off those parts with a small curve, respectively, from 2, 3,4, 6, on the soffit ; then with the parts 1, 2, 3, 4, on the greater dotted arch, cross them from k; trace through them, and you have half the soffit; mark them to the other side, and the soffit is complete.