The material must be cut in suitable shaped gores or segments.  In this article we shall confine ourselves to a 10-ft. balloon.  If the balloon is 10 ft. in diameter, then the circumference will be approximately 3-1/7 times the diameter, or 31 ft. 5 in.  We now take one-half this length to make the length of the gore, which is 15 ft. 7-1/2 in.  Get a piece of paper 15 ft. 7-1/2 in. long and 3 ft. wide from which to cut a pattern, Fig. 1.  A line, ab, is drawn lengthwise and exactly in the middle of the paper, and a line, CD, is drawn at right angles to ab and in the middle of the paper lengthways.  The intersecting point of ab and CD is used for a center to ascribe a circle whose diameter is the same as the width of the paper, or 3 ft.  Divide one-quarter of the circle

[Illustration:  Pattern for Cutting the Segments]

into 10 equal parts and also divide one-half of the line ab in 10 equal parts.  Perpendicular lines are drawn parallel with the line CD intersecting the division points made on the one-half line ab.  Horizontal and parallel lines with ab are drawn intersecting the division points made on the one-quarter circle and intersecting the perpendicular line drawn parallel with CD.  A line is now drawn from B to E and from E to F, and so on, until all the intersecting lines are touched and the point C is reached.  This will form the proper curve to cut the pattern.  The paper is now folded on the line ab and then on the line CD, keeping the marked part on the outside.  The pattern is now cut, cutting all four quarters at the same time, on the curved line from B to C. When the paper is unfolded you will have a pattern as shown in Fig. 2.  This pattern is used to mark the cloth, and after marked is cut the same shape and size.

The cloth segments are sewed together, using a fine needle and No. 70 thread, making a double seam as shown in Fig. 3.  When all seams are completed you will have a bag the shape shown in Fig. 4.  A small portion of one end or a seam must be left open for inflating.  A small tube made from the cloth and sewed into one end will make a better place for inflating and to tie up tightly.

It is now necessary to varnish the bag in order to make it retain the gas.  Procure 1 gal. of the very best heavy body, boiled linseed oil and immerse the bag in it.  The surplus oil is squeezed out by running the bag through an ordinary clothes wringer several times.  The bag is now placed in the sun for a thorough drying.  Put the remaining oil in a kettle with 1/8 lb. of beeswax and boil well together.  This solution is afterward diluted with turpentine so it will work well.  When the bag is dry apply this mixture by rubbing it on the bag with a piece of flannel.  Repeat this operation four times,

[Illustration:  Sewing Segments Together]

being sure of a thorough drying in the sun each time.  For indoor coating and drying use a small amount of plumbic oxide.  This will dry rapidly in the shade and will not make the oil hard.