The general plan upon which this book treats, is to work from the corner of a square, or from the centre of a circle, or from certain other angles, such as 7½ deg., 15 deg., 45 deg., 135 deg., etc. Dia. [III] is made for a purpose. It is likewise drawn within the angle of 15 deg., and is intended to represent the difference between sack and frock coats. Dia. [II] is arranged with a view to cutting purposes, for all parts are separate on a smooth surface, not in their natural position; but, by the aid of science, we know just how much they are out of their natural positions. Dia. [III] has the sidepiece changed, so that it laps with the forepart at the waist seam. In so turning the sidepiece down, the back will necessarily come along, and we find that it has shortened one-half of a number, on line 9 over the front. By turning the sidepiece in at the waist, the top of the back sidepiece seam falls backward one-half, thus making the square 18 for a three-seamed sack, as it is for a five-seamed frock.
The top of the sidepiece and back lap two seams, as they must be when sewed up, and the armholes are the same for both sack and frock coats. The lap of the sidepiece and forepart, and the lap of the bottom of the sidepiece and top of the back skirt, are explained as follows: A sack coat is wider at the back of the waist and runs down straighter than a frock. A straight line from the shoulder blade down to the seat is shorter than a line running down closer and in a greater curve toward the body. The circumference which the sack coat occupies at the back of waist is larger than that of a frock. The closer the garment fits to the body of the back the narrower it must become, and at the same time it must become longer.
Now, the position of the sidepiece in Dia. [III] just furnishes that extra length required, as well as the greater reduction in width. When the sidepiece is drawn even with the forepart at the waist seam, the lap of the sidepiece and the top of the skirt behind will crawl inward to the more hollow part of the waist, and the extra length is thereby taken up. The spring is not used in a sack, neither is the larger gore between the back and front; but both are omitted and a gore of about 1 in. is cut out, as for a sack, thus obtaining the larger width for the shorter back. The frock coat back has lost ¾ in length, hence the frock coat back on Dia. [III] is 14¼, while the sack coat back is only 13½, for the reason that it is broader at the junction with line 9 over the front. When both backs are thrown down and into a square of 20½, or in the shape of Dia. [I], the frock coat back reaches line 9 at a depth of 14¼, and the sack coat back reaches line 9 at a depth of 13½, but actually both have the same length from O. The extra length of the frock coat back and sidepiece above the bottom of the armhole is really a delusion, but the extra length of the sidepiece at the waist and at the back is used up, while the closer frock coat waist crawls more inward to the body.
Compare Article on “[Narrow and Broad Backs].” For illustration, let us suppose we have before us a man with a well-fitting sack,—not one that fits skin-tight at the waist and spreads out below over the seat, but one that is just what the ideal sack should be, which is loose, yet showing the outlines of the form. Say we button it in front, and draw over the waist a tape-line. We shall find that the more we draw it together the looser and wider it will appear to be; and the bottom of the back will become too short, because the line closer to the body requires more length, which in this case will be drawn up from the bottom. It shows too much width, because the circle closest to the body requires less of it. But more of this will be said in the article on “[Erect Forms].”
For particulars, it should be observed that Dia. [III] is in a square of 18, and that Dia. [VIII], or the three-seamed sack, is in the same square. A three-seamed sack would naturally be two seams less in the square than a five-seamed frock, which would bring the square for a three-seamed sack to 17½. But the turning of the sidepiece causes the square to enlarge ½, hence the square of a three-seamed sack is the same as on a five-seamed frock, or 20½ numbers. See Dia. [VIII B].
