Nor can it otherways be accounted for, why the Snow is perpetual, and the Cold so intense, on Mountains under the Equinoctial, and between the Tropics: but which admits an easy Solution on the above Hypothesis.[67] 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. [Sidenote: 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.