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tbofe gores that fonn the fuperCcies of a globe : and the 

 bcft method of cutting tlurn is to defcribe a pattern of 

 Wfwd or llilf card-paper, and to cut tlic filk or fluff upon it. 

 0:ie of thcfe pieces, that may fcrve as a pattern for others, 

 is reprcfcnted in Plate I. Pmviii/i/ies, Ji^t;. 2. In this figure, 

 fuppofe A E and B C to be two right hues pei-pi-'ndicular to 

 each other. Then find the circumference aufwering to the 

 given diameter of tlie balloon in feet and decimals oi a foot ; 

 and make AD and DE each equal to a quarter of the cir- 

 cumference, fo that AE may be equal to half the circum- 

 ference. Divide A D into 1 8 equal parts, and to the points 

 of divifion apply the lines fg, hi, kl, &c. paVallel to each 

 other, and perpendicular to AD. Divide the whole cir- 

 cumference into twice the givjn number of pieces, and make 

 D C and DB each equal to the quotient of this divifion ; fo 

 that B C will be equal to the greatcft breadth of one of thofe 

 pieces. Multiply this quotient or D C by the decimals 

 annexed io fg, vi-/.. 0.99619, and the product exprefl'es the 

 length of fg ; and multiply D C by the decimals annexed 

 to ki, and the produft exprefl'es the length of ii, &c. 

 Having thus found the lengths of all thefe lines, draw by 

 hand a curve line, paffing tiirough their extremities, and 

 this will be the edge of one quarter of the pattern. The 

 other quarters A B D, E B D, E D C, may be ealUy dcfcribed 

 bv applying to each of them a piece of paper equal to A 

 D C. Suppofe the diameter of the balloon to be 20 feet, 

 and that it is to be made of l ^ pieces. In order to draw 

 the pattern, find the circumference of the balloon, which is 

 62,83 feet, and dividing it by 4, the quotient is 15,7 feet : 

 confcquently AD and DE will be each equal to 15.7 feet. 

 Divide the circumference 62,83 ^7 ^4' O'' double the num- 

 ber of pieces that are to form the balloon ; and the quotient 

 2,618 feet will be the length of DC or BD ; therefore BC 

 is equal to 5,236 feet. Then dividing AD into 18 equal 

 parts, and drawing the parallel lines from the points of di- 

 vifion, find the length of thefe lines by multiplying 2,618 

 by the decimals annexed to that hne : thus, 2,618 multi- 

 plied by 0,99619 gives 2,608 feet for the length of y^V 

 and multiplying 2,618 by 0,98481, we fhall have 2,578 feet 

 for the length of hi, &c. The pieces cut after fuch a pat- 

 tern (houkl be left about one half or three quarters of an 

 inch all round larger than the pattei-n, in order to allow for 

 the feams. They may be joined by laying about half an 

 inch of the edge of one piece over the edge of the other, 

 and fewing them with a double Hitching. Mr. Blanchard 

 joins them veiy expeditioufly in the following manner. He 

 lays about half an inch of the edge of one piece flat over the 

 edgeof theother,and paffesa hot iron over it ; in doing which, 

 a piece of paper ought to be laid both under and over the filk. 

 The joining may be rendered more fecure, by running it 

 with a filk thread, and fticking a ribband over it. The 

 ribbands laid over feams may be ftuck with common glue, 

 provided the varnifii of the filk is properly dried. When the 

 glue is quite dry, the ribbands fhould be varniflied over, to 

 prevent their being unglued by the rain. 



To the upper part of the balloon there muft' be adapted 

 a valve, opening inward, to which is annexed a firing paJTing 

 through a hole made in a fmall round piece of wood which is 

 faftened to the lowell part of the balloon oppofite to the 

 valve, to the boat below it ; fo that the aeronaut may open 

 it as occafion requires, and let the inflammable air out of 

 the balloon. To the lower part of the balloon are fixed 

 two pipes of the fame fluff with the covering, fix inches in 

 diameter fur a balloon of thirty feet, and much larger for 

 balloons of greater fize, and long enough to reach the boat. 

 Thefe pipes are the apertures througli which tlie iuflam- 

 mable air b introduced into the ballo;<u. 



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The boat may be made of wicker-work, and covered with 

 leather, well painted or varniflied over. The beft me- 

 thod of fulpending it is by means of ropes, proceeding from 

 the net which goes over the balloon. This net fliould be 

 formed to the Ihape of the balloon, and fall down to the 

 middle of it, and have various cords proceeding from it to 

 the circumference of a circle, about two feet below the 

 balloon ; and from that circle other ropes fhould go to the 

 edge of the boat. This circle may be made of wood, or of 

 feveral pieces of (lender cane bound together. The mclhes 

 of the net may be fmall at top, agaiull which part of the 

 balloon the inflammable air exerts the greateft, force, and in- 

 creafe in fize as they recede from the top. A hoop has been 

 fometimes put round the middle of the balloon for failening 

 the net. This is not abfolutely neceffary ; but when ufed, 

 it is befl; made of pieces of cane bound together, and covered 

 with leather. When the balloon and its appendages are 

 conftrufted, the next objeft of importance is to procure 

 proper materials for filling it. With relpeft to thofe in- 

 flated by heated air, nothing need be faid tiU the method of 

 filling them is defcribed. 



Inflammable aV for balloons of the other kind may be 

 obtained in feveral ways ; but the beft methods are by ap- 

 plying acids to certain metals ; by expofing animal, vege- 

 table, and fome mineral fubftances, in a clofe veffcl, to a 

 ftrong fire ; or by tranfmitting the vapour of certain fluids 

 through red-hot tubes. 



In the firll of thefe methods, iron, zinc, and vitriolic acid, 

 are the materials moft commonly ufed. The vitriolic acid 

 muft be diluted with five or fix parts of water. Iron may 

 be cxpetled to yield in the common way about 1700 times 

 ityown bulk of gas; or 4^ ounces of iron, tire like weight 

 of oil of vitriol, and 22i ounces of water will produce one 

 cubic foot of inflammable air : fix ounces of zinc, an equal 

 weight of oil of vitriol, and 30 ounces of water, are neceffary 

 for producing the fame quantity. It is more proper to ufe 

 the turnings or chippings of great pieces of iron, as of 

 cannon, &c. than the tihngs of that metal ; becaufe the heat 

 attending the effervefeence will be diminiihed, and the di- 

 luted acid will pafs more readily through the interftices of 

 the turnings, when they are heaped together, than throurrh 

 the filings which ftick clofer to one another. The weight 

 of the inflammable air, thus obtained by means of acid of 

 vitriol, is, in the common way of prociinng it, generally 

 one-feventh part of the weight of common air ; and with the 

 neceffary precautions for philofophical experiments, lefs than 

 one-tenth of the weight of common air. The other elaltic 

 fluids, which are generated vfith the inflammable air, may 

 be fepai-ated from it by paffing the inflammable air througli 

 water, in which quick-Ume has been diflolved ; the water 

 will abforb thefe fluid's, cool the inflammable air, and pre- 

 vent its overheating the balloon, when it is introduced into 

 it. As white vitriol is fold much dearer than the vitriol of 

 iron, it will be a faving to make the inflammable air by 

 means of zinc and vitriolic acid, rather than of this acid and 

 iron : becaufe the fale of the white vitriol arifing from the 

 former will, in a degree, be a compenfation for the expence 

 of the materials. 



Inflammable air may alfo be obtained at a much cheaper 

 rate by the action of fire on various fubftances ; but the gas 

 thus obtained is not fo hght as that produced by the efler- 

 vefcence of acids and metals. The fubftances proper to be 

 ufed for this purpofe are pit-coal, afphaltum, amber, rock, 

 oil, and other minerals ; wood, and efpecially oak, camphor 

 oil, fpirits of wine, oether, and animal fubftances, whicii yield 

 air of different degrees and of various fpecific gravity. But. 

 pit-coal is the fubilance moft proper to be ufed. A pound, 



of 



