The cemented joints of the various pieces are ½ inch wide; they are then sewn by a machine, with three seams made with fine silk in the double or threefold material, and four rows of stitches in the fourfold material.
These joints or seams are then covered, outside and inside, with a strip of single silk 1⅕ inches wide, cemented on with a special varnish recently discovered by M. Lachambre.
The strips cemented by this new process have the double advantage of rendering the seams impermeable and restoring to the joints the resistance of which the stitching deprives them.
The varnish used for this cementing meets all requirements; it preserves the natural suppleness of the material, is unaffected by the balloon varnish, which has linseed oil for its basis, and is proof against water and changes of temperature.
The tests made with the joints thus constituted, proved that their resistance was greater than that of the adjoining parts, and Andrée, who only desires an equal strength throughout, naturally was very well satisfied with this result.
The seams are 4,811 yards long, with three or four rows of stitching, representing a line of single stitching equal to a length of 15,310 yards, and the total length of the cemented strips is nearly 9,842 yards.
The two hemispheres of the balloon were first formed; their weight was 2,116 lbs., and before proceeding to the last equatorial closing seam, they were given three coats of Arnoul’s varnish (the best balloon varnish hitherto tried); a fourth coat being given after the two halves had been joined together, on the premises of the “Palais du Champ de Mars,” remaining from the 1889 Exhibition.
Net.—The net of the polar balloon is composed of 384 hemp cords, ⅙ inch thick by 211 feet 7 inches long, each having a breaking strain of not less than 873 lbs. (in the tests made the minimum result was 925 lbs., while the maximum was 1,190 lbs.).
Each cord is jointless; its two ends are fixed, at the upper pole, to a cordage ring or crown measuring 26 inches in diameter and 2⅓ inches in thickness. There are no knots in this net, the cords being interwoven at their crossing points, one being passed through the other; it was in this way that the “Henri Giffard” captive balloon was finished in 1878.