CHAPTER XXXXVI.
Section 254. THE Subject of depressing torrents requires an accurate Investigation: as it will serve to point out the proper Time of Day or Night, when an Aironaut ought so to calculate his Voyage, as to arrive over the Middle of the Channel, or Arm of the Sea, at some particular Hour: in order to wait for a Sea Breeze which may waft him to the other Side.
A Point not difficult to be ascertained.
Also, this Idea of depression, if properly considered and digested; may prove a sufficient Foundation on which to establish a new Theory of the Weather, so ill determined at present, from its aggregate Weight or Elasticity only, as indicated by the Barometer.
255. If a Conjecture may be formed on a Subject, material in itself, yet of which so little is actually known; woud not the proper Time of undertaking a Voyage over the Channel be such, that the Aironaut shoud find himself three Parts of the Way across, by nine o’Clock in the Morning?
256. In warmer Climates, where the Seasons are more regular; the Land-Breeze blows to Sea from Midnight till X. in the Morning: at which Time, the Sea-Breeze blows to Land; continues till V. or VI. in the Evening; and is succeeded by a calm, which lasts till Midnight.
Whence it follows, that during the Time of the Sea-Breeze, there is a constant Tendency towards a gulph of air, along the Middle of the Channel: the Equilibrium of which is as constantly supplied by a Depression of the upper and in general cooler Strata of Air; and therefore a dangerous Time for the Passage of Balloons.
On the contrary, during the Night, and till ten in the Morning, there is an Accumulation of Air, along the Middle of the Channel: which consequently is a proper Time to ensure a safe Passage; by the Assistance of wings, or some propulsive Machinery.
Of the horizontally calm mediocèanal depressing Current.
257. The Deficiency or Vacuity being supplied from the etherial Regions; it might be taken for granted, that such Ether must be considerably lighter than the adjacent common Air on an equal Level, and therefore proportionably dangerous for the Passage of Balloons.