Beginning with the square, Fig. 1, fold 1 on 2, and crease with the thumb-nail, thus obtaining Fig. 2.
To obtain Fig. 3, divide the 1800 fold into two and a third parts, and fold the right part on the adjoining one, folding from o in Fig. 2. For Fig. 4, reverse the position of the fold, placing the rear face in front, and fold the remaining third part over the other fold. For Fig. 5, fold the edge 1 to adjoin the edge 2 in Fig. 4, making 1-0 and 2-0 meet. For Fig. 6, bisect the fold of Fig. 5, folding the left half under the right half.
Fold to Fig. 5, and cut from 1 to 2. Points 1 and 2 are equally distant from o.
Fold to Fig. 6, and cut from 1 to 2. Point 2 is nearer to 4 than to 3.
Fold to Fig. 6, and cut from 1 to 2. Point 2 is the tangential union of the semicircle and the line 3-0. The semicircle must have its centre on the line 1-0.
Fold to Fig. 5, and cut from 1 to 2.