82 CONSTRUCTION OF BALLOONS. 



whether it has boiled enough } which may be known by observing 

 whether, when rubbed between two knives and then separated from 

 one another, the varnish forms threads between them, as it must then 

 be removed from the fire ; when nearly cool, add about an equal 

 quantity of spirit of turpentine : in using the varnish, the stuff must 

 be stretched and the varnish lukewarm : in twenty.four hours it will 

 be dry." As the elastic resin, known by the name of Indian rubber, 

 has been much extolled for a varnish, the following method of 

 making it, as practised by Mr. Blanchard, may not prove unaccept. 

 able : Dissolve elastic resin, cut small, in five times its weight of 

 rectified essential oil of turpentine, (ethereal spirit of turpentine of 

 the shops), by keeping them some days together ; then boil one 

 ounce of this solution in eight ounces of drying linseed oil for a few 

 minutes ; strain the solution and use it warm. The car or boat is 

 best made of wicker-work, covered with leather, and painted ; and 

 the proper method of suspending it, is by ropes proceeding from the 

 net which goes over the balloon. The net should be formed to the 

 shape of the balloon, and fall down to the middle of if, with various 

 cords proceeding from it to the circumference of a circle about two 

 feet below the balloon; and from that circle other ropes should go 

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

 several pieces of slender cane bound together. The meshes of the 

 net may be small at top, against which part of the balloon the inflam- 

 mable air exerts the greatest force ; and increase in size as they 

 recede from the top. 



With regard to the rarefied-air machines, Mr. Cavallo recom. 

 mends first to soak the cloth in a solution of sal-ammoniac and com- 

 raon size, using one pound of each to every gallon of water ; and 

 when the cloth is quite dry, to paint it over in the inside with some 

 earthy colour, and strong size or glue. When this paint has dried 

 perfectly, it will then be proper to varnish it with oily varnish, 

 which might dry before it could penetrate quite through the cloth. 

 Simple drying linseed oil will answer the purpose as well as any, 

 provided it be not very fluid. If a parachute is required, it should 

 be constructed so as when distended to form but a small segment of 

 a sphere, and not a complete hemisphere ; as the weight of this ma- 

 chine is otherwise considerably increased, without gaining much in 

 the opposing surface. The parachute of M. Garnerin is particularly 

 defective in too great extension of its diameter ; an unnecessary ad- 

 dition to its weight of a lining of paper both withinside and without; 



