319. Hint for an Umbrella-Pendulum or Valve-Swing, to project the Balloon in a Calm in the ethereal Regions, above the Station of Clouds; where the Resistence from the Air is much less than at the Surface of the Earth. [Sidenote: Hint for a _Valve-Swing_ to project the Balloon in a calm and elevated Atmosphere.] Let the Car of the Balloon be perforated so as to admit a light Gordon Mast, or Pole 18 or 20 Feet long, perpendicularly throu’ it. (315, 3.) At the Distance of five Feet from the upper End of the Pole, a light hollow cylindric Tube of Iron, one Foot long, as a Bolt, shoud be put throu’ it, at right Angles: so as to play smoothly in two Iron Bends, fixed in the Car; one Bend so far moveable, as to rise with a Hinge to admit the End of the Bolt; the other Part of the Bend to be perforated: throu’ which a hollow Staple is to be fastened, with a spring Cotterel chained: this Apparatus will prevent the Pole from turning round. Two light Frames of Wood, of a parallelogrammic Form, each twelve Feet by six, and covered with varnished Silk, are to be hooked, one on each of the opposite Sides of the Pole, from its lower End upwards; the Frames to be moveable in such a Manner, that on pressing the Pole one Way on the Axis or Bolt, the Frames shall lie close; but on recovering the Pressure, the Frames shall expand and open, so as to form an obtuse Angle with each other, or to lie almost in the same Plane, when the Recovery is made briskly, and with a Degree of Strength. A Handle of Wood, the same Size with the Bolt, may be fastened throu’ the Substance of the Pole near its upper End. The Operator is to stand in the Car, and work the Pole backwards and forwards, which will give a progressive Motion to the Balloon in a Calm. This Method may possibly prove more effectual than the Umbrella-Wheels, on an horizontal Axis, of Mons. Carra;[108] as the Umbrella-Pendulum is easily unrigged, removed, and brought into the Car, in Case of a Whirlwind; by Means of a _circular_ Rope fastened to the Axis or Bolt, one End being in the Car, and the other put throu’ the Aperture at the Bottom, and brought up from the Outside again into the Car. The Umbrella-Pendulum may be made to turn round horizontally on the Bolt; the Ends of the Bolt being fastened under a circular hinged Socket, or Groove, of Iron. CHAPTER LXII. DEFECTS, IN THE COMPOSITION FOR BALLOONS, REMEDIED. ALSO ON THE COCHUC-VARNISH. Section 320. Balloons are defective in the Composition for _the Varnish_; which, till lately, was incapable of rendering the Balloon completely and _durably_ Air-tight. 321. It was sometime ago reported at Paris, that Mr. Dutourny de Villiere had undertaken to construct a Balloon so truly _impèrmeable_, that he woud warrant the Duration of it, for _several Weeks_ in the Air.