It should also be noticed that there is no break in the continuity of the voyages previously recorded with those belonging to the siege. The need was urgent, and there was no time to originate fresh constructions, or introduce new principles. The old invention as it stood was to be stimulated into success, if success were to be had. But it was necessary that new balloons should be made, and at once, for not a balloon in Paris at the commencement of the siege proved on examination to be sufficiently trustworthy to pass over the besieging lines in safety. To remedy at once this state of affairs extensive works were commenced. No pains were spared to avoid failure, and no detail was thought trifling enough to be overlooked.
The material was naturally the first consideration; this needed to be of even texture, without fault of manufacture, and above all strong. The fabric of greatest strength it is well known is that of silk, but silk was far too costly.
The material decided upon was calico, either white or coloured. That it should be gas-tight it was varnished with a mixture of linseed oil and oxide of lead. To make the oil consistent and dry the varnish was applied by a rag, and not by means of a brush, so that all the pores or chance apertures in the material were sealed and rendered thoroughly impervious to the escape of gas. This application was made to both sides when time permitted, but generally the outside alone was coated.
Two factories were established, one at the Orleans, and the other at the Northern Railway Station. The former was placed under the management of M. Godard; the latter under the direction of MM. Yon and Dartois. MM. Godard and Yon are known in London as having superintended and directed the ascents of M. Giffard's Captive balloon, at Ashburnham Park, Chelsea, in 1869. Both factories were under the direction of the Post Office.
The material employed at the Northern Station was white, that at the Orleans Station coloured, and both places adopted the same method of procedure in commencing. The size of each gore for the intended balloon was carefully drawn on a horizontal plan, just as is done in the construction of a globe. These gores were sewn together by hand at the Orleans Station, and by sewing machines at the
