Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . e military balloons are made ofthe so-called ponghee silk, which is of an inferior quality,and therefore cheaper. One layer is sufficient on account of thegreat strength of the material. When cambric is used, it isnecessary to have two layers, which are placed diagonally, oneon top of the other, so that the pattern of the one is at an angleof 45 degrees to that of the other. This much increases the BALLOON CONSTRUCTION, ETC. 181 strength of the covering.
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . e military balloons are made ofthe so-called ponghee silk, which is of an inferior quality,and therefore cheaper. One layer is sufficient on account of thegreat strength of the material. When cambric is used, it isnecessary to have two layers, which are placed diagonally, oneon top of the other, so that the pattern of the one is at an angleof 45 degrees to that of the other. This much increases the BALLOON CONSTRUCTION, ETC. 181 strength of the covering. It is necessary that it should be veryclosely woven throughout, and that it should be in all places ofthe same strength, special machines having been designed fortesting its resisting power. All envelopes made of silk or cottonrequire to be varnished in some way. The oldest method was tocoat it with rubber solution, as proposed by Charles, applied byhot rollers. This is also vulcanised with sulphur, which helpsto preserve it. However, light has the effect of gradually dis-integrating rubber, and this can to some extent be prevented by. FlG. 108.—Making balloon envelopes in Eiedingers factory, inAugsburg. colouring it with a yellow paint. A better plan is to varnish theenvelope with linseed oil, though it must be admitted that ithas the unpleasant property of becoming very sticky in hotweather. Great care must be taken in storing such balloons, asthey are very liable to catch fire spontaneously. The methodsthat were employed in making the old varnishes are unfortunatelyno longer known. Several other things have also been used formaking the coverings airtight; but nothing better is known thanlinseed oil varnish, or rubber solution. One square foot ofponghee silk, as used for French military balloons, withfive coats of varnish weighs 1*2 ounces, and one square foot of 182 AIESHIPS PAST AND PEE SENT.
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Keywords: ., bookcentury1900, bookdecade1900, bookpubl, booksubjectaeronautics
