And if the Balloon Art coud be perfected, so as to make them stationary at any Height; this Circumstance woud afford excellent Opportunities of proving the Heights by the Barometer: besides which, the Distance also has been obtained: a Point not before attempted.[103] CHAPTER LVIII. OF THE AIR-BOTTLE BALLOON. Section 311. Till the Particulars of Meunier’s Invention are made public,[104] an additional _Air-tight_ Balloon, or Air Bottle, at least 15 Feet in Diameter, of a _globular_ Form, appended below the Car, and furnished with a _Condenser_, to be worked by _pulling upwards_, or, as the Bellows of an Organ, by the alternate Motion of the Feet of the Aironaut, standing upright in the Car, may be used instead of the interior Balloon; to keep the _great Balloon_ at a _given_ Height: and consequently prevent the Aironaut _from rising too high_: to atchieve which Purpose, during the _first Ascent_; a Rope or Balancer may be used, a Mile and half long, fastened to the Car, and rising with the Balloon, (to _check_ its Power of _Ascent_,) till an Equilibrium is produced: at which Instant, on Sight of the _white_ Flag from the Car, the Balance-Rope is to be cut, by the Operator _below_. (Section 302.) If the Aironaut perceives by the Rise of the _Barometer_, that the Balloon descends; he may throw out a _little_ Ballast, (perhaps a Pound or two), and then wind up his Balancer, or suffer it to remain at any Length, at his Option. 312. By keeping the Balloon at a given Height _only_; no Gass is expended in preventing the necessary Tendency of Balloons to a perpetual Elevation: also, during the self Descent of the Balloon; by opening the Air-Bottle, the Aironaut will supersede the Necessity of throwing out Ballast, for a Re-ascent. 313. The Air-Bottle-Balloon shoud be covered by a strong _light_ Net, of a Dimension rather less than the Bottle, which will hinder it from bursting: the Resistence of the _condensed_ Air within, being then chiefly on the Net, and but little on the Bottle. The Net may be made of Silk and Cotton Thread; lest the Meshes, by the Pressure of the Knots, shoud eat into the Bottle. CHAPTER LIX. SUPERIORITY OF THE AIR-BOTTLE TO AN INTERIOR BALLOON. Section 314. The Air-Bottle can be attended with no Sort of Danger. For, if it burst; the only Effect is to raise the Balloon: which is made to descend, at Pleasure, by opening either the _lower_ or upper Valve. Whereas an interior Balloon condensed with common Air, presses against the surrounding exterior Gass: and the Gass, against the +inside+ of the _great Balloon_, when the latter is in an elevated and rarefied Atmosphere; which Atmosphere, in Proportion to its Height, makes _less_ Resistance to the _Outside_ of the great Balloon: and thereby encreases its Tendency to a Rupture.