With chalk dividers construct upon the black-board an equiangular triangle, upon a given line, by means of arcs.

Directions for drawing diagram:

Bisect the back edge of the paper. On the left edge place a point four inches from the back left corner; place one directly opposite on the right edge; also place one midway between points. The point last placed shall be the middle point of a four-inch horizontal line. Draw the line. From the right end of this line let fall a perpendicular six and one-fourth inches in length. From the lower end of this line draw a perpendicular four inches to the left. Connect the left ends of horizontal lines.

On these vertical lines place points one-fourth inch from their upper ends and below set off three two-inch spaces, numbering points as in the cube and square prism.

Join all opposite points. Cut the corners of the upper margin as in the cube. Open the dividers equal to the length of the short side of the oblong; place the metal point at point No. 3 to the right; place the pencil point at point No. 2; beginning there, construct an arc about two and one-half inches in length to the right.

Place the metal point at point No. 2; construct an arc to the right, intersecting the preceding arc; join intersection of arcs with points 2 and 3.

Construct a corresponding triangle on the left side of the same oblong.

Transfer to card-board to the scale of two inches to three inches.

Crease, cut, fold, and glue, using the circular margins on the sides of the triangles.