Signs of progressive Motion deceitful.
18. These are equivocal and deceitful.
When the Aironaut has lost Sight of the Earth by intervening Clouds; the Balloon seems at Rest, and only the lower Clouds appear to move: whereas the contrary may be true, the Clouds may rest, and only the Balloon move.
In this Case, Attention must be paid to the half Mile white Flag, whose Situation and Motion must be observed, with respect to the Balloon, and to the Earth before the Cloud intervened. If the Flag retains its Situation with Respect to the Balloon, it may be inferred that no Change in the Direction has happened: if its Situation alters, the Sun or Compass is to be observed: and an Estimate made of the new Current of Air by which the Balloon is affected: its Velocity, Sound, Temperature, &c.
To descend when lost.
19. But to acquire a Certainty of course, it will be proper to descend below the Cloud: or move by Compass, Map, and a Knowledge of the Country: or try the long Cable ([Section 13].)
Signs of Wind horizontal.
20. It is likewise necessary to know the Signs of Wind, or Currents of Air.
SIGNS OF NEW AND SUDDEN HORIZONTAL CURRENTS.
When the Feathers, Balloon-Flag, or Ribbon, compared with Sun or Compass, take a new and sudden horizontal Direction.