Fig. 1.
In making a balloon the first thing to be done is to take into consideration how many gores, or strips, will be required to form a balloon of any given diameter. For instance, if a balloon be required of the circumference of 3 feet, there will be twelve gores each 18 inches in length (that being half the circumference), and 3 inches in width at the equator, but tapering at each extremity, as will be hereafter described. Now divide the paper of the pattern gore into four equal parts, and then describe a circle in the centre ([Fig. 1]).
Fig. 2.
Divide one quadrant of the circle into any given number of parts—say seventeen. Then drop perpendiculars parallel with line C from each point of the divisions, intersecting line B in the quadrant. Now divide line B from centre of circle to end of pattern in seventeen equal parts, and raise perpendiculars from each point of division, as in [Fig. 2].
Fig. 3.
Next draw horizontal lines, or measure off with compasses from each point of division in the quadrant, cutting or intersecting the seventeen corresponding lines as shown, and with a free hand, or by the aid of a French curve, connect all these points together, as shown in [Fig. 3].